Fanconi Anemia, Complementation Group A

A number sign (#) is used with this entry because Fanconi anemia of complementation group A (FANCA) is caused by homozygous or compound heterozygous mutation in the FANCA gene (607139) on chromosome 16q24.

Fanconi anemia is a clinically and genetically heterogeneous disorder that causes genomic instability. Characteristic clinical features include developmental abnormalities in major organ systems, early-onset bone marrow failure, and a high predisposition to cancer. The cellular hallmark of FA is hypersensitivity to DNA crosslinking agents and high frequency of chromosomal aberrations pointing to a defect in DNA repair (summary by Deakyne and Mazin, 2011).

Soulier et al. (2005) noted that the FANCA, -C, -E, -F, -G, and -L proteins are part of a nuclear multiprotein core complex which triggers activating monoubiquitination of the FANCD2 protein during S phase of the growth cycle and after exposure to DNA crosslinking agents. The FA/BRCA pathway is involved in the repair of DNA damage.

Some cases of Fanconi anemia have presented with a VACTERL (192350) or VACTERL-H (276950, 314390) phenotype. In a group of 27 patients with Fanconi anemia group D1 (605724) due to biallelic mutations in the BRCA2 gene (600185), Alter et al. (2007) found that 5 patients had 3 or more VATER association anomalies and 1 was diagnosed with VACTERL-H. A VATER phenotype has also been reported in Fanconi anemia of complementation groups A, C (227645), E (600901), F (603467), and G (602956); VACTERL-H has also been described in patients with FANCB (300515) mutations (McCauley et al., 2011). Savage et al. (2015) added patients with FANCI (609053) to this list and stated that patients with FANCD2 (227646) and FANCL (614083) had also been reported to have features of VACTERL association.

Genetic Heterogeneity of Fanconi Anemia

Other Fanconi anemia complementation groups include FANCB (300514), caused by mutation in the FANCB (300515) on chromosome Xp22; FANCC (227645), caused by mutation in the FANCC (613899) on chromosome 9q22; FANCD1 (605724), caused by mutation in the BRCA2 (600185) on chromosome 13q12; FANCD2 (227646), caused by mutation in the FANCD2 gene (613984) on chromosome 3p25; FANCE (600901), caused by mutation in the FANCE gene (613976) on chromosome 6p21; FANCF (603467), caused by mutation in the FANCF gene (613897) on chromosome 11p15; FANCG (614082), caused by mutation in the XRCC9 gene (FANCG; 602956) on chromosome 9p13; FANCI (609053), caused by mutation in the FANCI gene (611360) on chromosome 15q26; FANCJ (609054), caused by mutation in the BRIP1 gene (605882) on chromosome 17q22; FANCL (614083), caused by mutation in the PHF9 gene (FANCL; 608111) on chromosome 2p16; FANCN (610832), caused by mutation in the PALB2 gene (610355) on chromosome 16p12; FANCO (613390), caused by mutation in the RAD51C (602774) on chromosome 17q22; FANCP (613951), caused by mutation in the SLX4 gene (613278) on chromosome 16p13; FANCQ (615272), caused by mutation in the ERCC4 gene (133520) on chromosome 16p13; FANCR (617244), caused by mutation in the RAD51 gene (179617) on chromosome 15q15; FANCS (617883), caused by mutation in the BRCA1 gene (113705) on chromosome 17q21; FANCT (616435), caused by mutation in the UBE2T gene (610538) on chromosome 1q31; FANCU (617247), caused by mutation in the XRCC2 gene (600375) on chromosome 7q36; FANCV (617243), caused by mutation in the MAD2L2 gene (604094) on chromosome 1p36; and FANCW (617784), caused by mutation in the RFWD3 gene (614151) on chromosome 16q23.

The previously designated FANCH complementation group (Joenje et al., 1997) was found by Joenje et al. (2000) to be the same as FANCA.

A patient originally reported to have Fanconi anemia of complementation group M (FANCM) due to mutation in the FAAP250 gene (609644) by Meetei et al. (2005) was subsequently found by Singh et al. (2009) to have FANCA.

Clinical manifestations of Fanconi anemia include pre- and postnatal growth retardation; malformations of the kidneys, heart, and skeleton (absent or abnormal thumbs and radii); a typical facial appearance with small head, eyes, and mouth; hearing loss; hypogonadism and reduced fertility; cutaneous abnormalities (hyper- or hypopigmentation and cafe-au-lait spots); bone marrow failure; and susceptibility to cancer, predominantly acute myeloid leukemia. The life expectancy of FA patients is reduced to an average of 20 years (range, 0-50) (summary by Joenje and Patel, 2001).

Giampietro et al. (1993) pointed to the 'extreme clinical heterogeneity' among patients with Fanconi anemia based on an analysis of clinical data from 370 patients enrolled in the International Fanconi Anemia Registry. Of these, 220 (60%) represented probands with congenital malformations. In addition to short stature, cafe-au-lait spots, and radial-ray and renal malformations, affected patients presented with cardiac, gastrointestinal, central nervous system, and various skeletal abnormalities. Genital anomalies were common in male patients. Approximately 50% of the patients had radial-ray abnormalities, which ranged from bilateral absent thumbs and radii to a unilateral hypoplastic thumb or bifid thumb. Among the patients with congenital malformations, the diagnosis of Fanconi anemia was made in only 28% before the onset of hematologic manifestations. About one-third of all patients enrolled in the registry did not have congenital malformations; of these patients, 85% had at least one of the following: skin pigmentation abnormalities, microphthalmia, or height, weight, or head circumference in the lowest 5% for their age. Minor congenital anomalies were noted in approximately 20% of these patients.

Leukemia is a fatal complication (Garriga and Crosby, 1959) and may occur in family members lacking full-blown features.

Zaizov et al. (1969) described 2 sisters and a brother with pancytopenia similar to that of Fanconi anemia but without congenital malformations. Chromosomal changes similar to those of Fanconi anemia were present and patchy areas of hyperpigmentation were noted in 2 of the sibs.

Hirschman et al. (1969) reported 2 brothers with aplastic anemia similar to Fanconi anemia but without associated congenital anomalies. Both responded to androgen therapy and showed increased chromosomal breakage as in Fanconi anemia. One had a stable translocation chromosome in bone marrow cells. The other's skin fibroblasts showed increased susceptibility to 'malignant' transformation by SV40 virus, as in Fanconi anemia. Skin fibroblasts of the mother and a sister, both normal, also showed increased susceptibility to 'malignant' transformation. Alter (1981) considered the cases of Hirschman et al. (1969) to be instances of Fanconi anemia.

Swift et al. (1974) concluded that male heterozygotes for Fanconi anemia have a risk of malignant neoplasm 3.4 times that of the general population.

Li and Potter (1978) reported typical Fanconi anemia in a close relative of the 5 sibs with hypoplastic anemia reported by Estren and Dameshek (1947). The parents of the Fanconi patient were second cousins and both were first cousins of the 5 sibs. Li and Potter (1978) suggested that these 5 sibs may have been genetic compounds for Fanconi anemia and Blackfan-Diamond hypoplastic anemia (105650).

Welshimer and Swift (1982) studied families of homozygotes for ataxia-telangiectasia (AT; 208900), Fanconi anemia, and xeroderma pigmentosum (XP) to test the hypothesis that heterozygotes may be predisposed to some of the same congenital malformations and developmental disabilities that are common among homozygotes. Among XP relatives, 11 of 1,100 had unexplained mental retardation, whereas only 3 of 1,439 relatives of FA and AT homozygotes showed mental retardation. Four XP relatives and no FA or AT relatives had microcephaly. Idiopathic scoliosis and vertebral anomalies occurred in excess in AT relatives, while genitourinary and distal limb malformations were found in FA families. Considerable intergenic heterogeneity has been found in xeroderma pigmentosum and some in ataxia-telangiectasia.

Berkovitz et al. (1984) concluded that abnormal sexual development in Fanconi anemia represents hypergonadotropic hypogonadism.

De Vroede et al. (1982) observed simultaneous onset of pancytopenia in a brother and sister, 5 years apart in age, suggesting possible exposure to a common external agent. One of the patients showed ropalocytosis, i.e., club-shaped cell processes, affecting the erythropoietic series from basophilic erythroblasts to reticulocytes.

Macdougall et al. (1990) described FA in 25 black African children seen in Johannesburg over an 11-year period. Seventeen (68%) of the children died during the period of observation. Leukemia was the terminal event in 2. Response to androgens was poor and most patients required regular transfusion. Mean age of death was 9.8 years and the mean time between diagnosis and death 2.3 years.

According to Auerbach (1992), a review of all cases of FA reported to the International Fanconi Anemia Registry indicated that at least 15% manifested acute myelogenous leukemia (AML) or preleukemia. These patients usually have karyotypically abnormal bone marrow clones but do not exhibit chromosomal translocations involving breakpoints associated with specific oncogenes.

Hagerman and Williams (1993) illustrated the characteristically short thumb and a cafe-au-lait spot in a patient with Fanconi anemia, together with cytogenetic studies showing chromatid fragments and a dicentric chromosome.

Young and Alter (1994) concluded that the proportion of FA homozygotes without external anomalies is underestimated by literature review. Literature reports of homozygotes identified because they had affected sibs indicated that at least 25% do not have anomalies. Young and Alter (1994) stated that such patients represent one end of the spectrum of FA.

Kwee et al. (1997) reported atypical cases of FA in 2 elderly sibs. The 56-year-old proband had no hematologic findings of FA and was found by complementation study to belong to FA group A. Her elder brother had thrombocytopenia and leukopenia, and died of heart failure, uremia, and anemia at the age of 50. Earlier cytogenetic investigation in the brother did not show hypersensitivity to mitomycin C.

In a study of 54 patients with FA, Wajnrajch et al. (2001) found that endocrinopathy was a frequent finding, occurring in 81% of patients. Seventy-two percent of patients had hyperinsulinemia, 25% had impaired glucose tolerance or overt diabetes mellitus, 44% had a subnormal response to growth hormone stimulation, 100% had abnormal spontaneous growth hormone secretion profiles, and 36% had thyroid hormone deficiency. The patients with low growth hormone responses tended to have a greater degree of growth retardation than the group as a whole, and stature was significantly worse for those with hypothyroidism. The patients with no demonstrable endocrinopathy had a mean height of 2 standard deviations below normal, demonstrating that a significant degree of short stature is typical of FA. Patients with complementation group A seemed to have a relatively mild endocrine phenotype, whereas patients with complementation group C had greater impairment of stature and a greater tendency toward primary hypothyroidism.

Bakhshi et al. (2006) described the case of a 17-year-old boy with a seemingly unique lymphocyte mitomycin-C (MMC)-sensitive chromosomal breakage syndrome. He had failure to thrive, microcephaly, slight facial dysmorphism, and constitutional short stature but no other phenotypic or hematologic manifestations of FA. He developed B-cell lymphoma of the neck, which was treated with standard doses of alkylating agents without adverse side effects related to chemotherapy. Normal erythrocyte corpuscular volume, MMC-insensitive fibroblasts, and the occurrence of lymphoma rather than AML set this patient apart from typical FA. The combination of constitutional dwarfism, microcephaly, MMC-sensitive lymphocytes, and susceptibility to lymphoma appeared to represent an unusual constellation of symptoms among genetic disorders.

Krausz et al. (2019) studied a 43-year-old infertile Spanish man (patient 04-170), born of first-cousin parents, who was found to be homozygous for a missense mutation in the FANCA gene. The proband had nonobstructive azoospermia, and testicular biopsy showed complete absence of germ cells in the tubules (Sertoli cell-only syndrome type I; see 400042). The DEB-induced chromosomal breakage test was consistent with FA somatic mosaicism, and the presence of 2 to 3% wildtype alleles on next-generation sequencing suggested a possible mechanism of genetic reversion by back mutation. In the proband's azoospermic brother, who was also homozygous for the FANCA mutation, DEB-induced chromosomal breakage was present in the majority of cells, indicating typical complete FA. The proband showed some facial dysmorphism, but his brother did not have dysmorphic features. Although previously the brother had exhibited mildly low platelets, red blood cells, and leukocytes, no further analysis had been performed at that time; however, follow-up laboratory evaluation after molecular diagnosis showed a pronounced decrease of all 3 cell types.

In 2 brothers and a third unrelated patient, Lohr et al. (1965) found marked reduction of red cell, leukocyte, and platelet hexokinase activity. This is apparently a different defect from the hexokinase deficiency (235700) that is limited to red cells and results in hemolytic anemia alone. A consistent defect in hexokinase cannot be considered as proved (Brunetti et al., 1966).

Joenje et al. (1979) found deficiency of red cell superoxide dismutase in Fanconi anemia by 2 independent methods of assay. The activity per antigenic unit and the electrophoretic mobility of the enzyme were normal, suggesting that the deficiency is due to a regulatory disturbance, not a mutation in the structural gene for the enzyme.

Joenje and Patel (2001) noted that patients with Fanconi anemia have elevated levels of serum alpha-fetoprotein (Cassinat et al., 2000).

The G2 phase of the cell cycle is very long in Fanconi anemia (Dutrillaux et al., 1982), a feature that might be used for diagnosis when no other manifestations are present (Schindler et al., 1985). Schindler et al. (1985) performed tests with BrdU-Hoechst flow cytometry, with the ratio of G2 to G1 as the measure. The results showed arrest at the G2 phase in lymphocytes. Similar findings have been found in ataxia-telangiectasia (Schindler et al., 1987). Heterozygotes for both conditions have intermediate values (Schinzel, 1991).

Using family data on Fanconi anemia, Rogatko and Auerbach (1988) tested a new method of segregation analysis when no information about mode of ascertainment is available. The results confirmed a monogenic autosomal recessive mode of inheritance.

Since particular mutation predisposes to multiple chromosomal breaks (Schroeder et al., 1964; Bloom et al., 1966), spontaneous chromosome breakage is a feature of FA.

Bloom syndrome (210900) is another single gene disorder accompanied by chromosomal breakage and predisposition to leukemia. Schroeder and German (1974) showed that aberrations were more numerous in Fanconi cells than in Bloom cells. In Bloom syndrome most interchanges were between homologous chromosomes, whereas in Fanconi anemia they were usually between nonhomologous chromosomes.

In a review of cytogenetic studies of FA-associated leukemias, Auerbach and Allen (1991) found a high frequency of monosomy 7 and duplications involving 1q. There were no occurrences of t(8;21), t(15;17), or abnormalities of 11q, which are associated with M2, M3, and M5 leukemias, respectively. The mean age of death in FA patients developing leukemia was 15 years.

Callen et al. (2002) studied several markers of telomere integrity and function in lymphocytes of FA group A patients and age-matched controls. A higher frequency of extrachromosomal TTAGGG signals and of chromosome ends with undetectable TTAGGG repeats were observed in FA cells by FISH, suggesting intensive breakage at telomeric sequences. Consistent with previous reports, quantitative FISH analysis showed an accelerated telomere shortening of 0.68 kb in both arms of FA chromosomes. A 10-fold increase in chromosome end fusions was observed in FA cells, despite normal binding of TRF2 (602027), a telomere binding factor that protects human telomeres from end fusions. The authors concluded that telomere erosion in FA is caused by a higher rate of breakage at TTAGGG sequences in vivo in differentiated cells, and that the increased occurrence of end fusions is independent of TRF2 binding.

Fanconi anemia complementation group A is caused by mutation in the FANCA gene, which maps to chromosome 16q24.3 (Fanconi Anaemia/Breast Cancer Consortium, 1996).

Exclusion Studies

By linkage studies in families from the International Fanconi Anemia Registry which contained 2 or more affected offspring, one or more offspring from consanguineous marriages, or multiple affected children in collateral sibships, Auerbach et al. (1989) excluded the long arm of chromosome 19 as the location for the Fanconi anemia mutation. Chromosome 19q had been considered a candidate location for the gene because 3 DNA repair genes (126340, 126380, 194360) are located there.

Poon et al. (1974) showed that cells from patients with Fanconi anemia are deficient in their ability to excise UV-induced pyrimidine dimers from their DNA. They are capable, however, of single strand break production and unscheduled DNA synthesis. From this the authors inferred deficiency in an exonuclease which specifically recognizes and excises distortions in the tertiary structure of DNA. Hirsch-Kauffmann et al. (1978), like some other workers, could find no defect in exonuclease but found reduction in DNA ligase activity in both a patient and the heterozygous mother.

Fujiwara et al. (1977) presented evidence that Fanconi anemia fibroblasts have an impaired capacity of removing DNA interstrand crosslinks induced by mitomycin C. They favored the view that a DNA crosslink repair deficiency is responsible for chromosomal damage in this disorder. Wunder et al. (1981) suggested that the defect in Fanconi anemia is in the passage of DNA-repair-related enzymes from the site of synthesis in the cytoplasm to the site of action in the nucleus. Studying the placenta of an affected infant, an unusual distribution of DNA topoisomerase was noted: high in the cytoplasm, very low in the nuclear sap. Whether the defect resides in the nuclear membrane or in the enzyme molecule is not clear. Wunder (1984) extended the studies suggesting that relatively high cytoplasmic DNA topoisomerase I in Fanconi placenta and fibroblasts may be due to an impediment to entry into the nucleus or perhaps binding to chromatin.

In somatic cell hybrid studies, Duckworth-Rysiecki et al. (1985) presented evidence for the existence of at least 2 FA complementation groups. They correspond to phenotypically distinct classes of cells exhibiting different rates of recovery of semiconservative DNA synthesis after treatment with DNA crosslinking agents in culture (Moustacchi et al., 1987) and different rates of removal of DNA crosslinks as shown by electron microscopy (Rousset et al., 1990). However, these studies do not provide a reliable method for determining the complementation group of a given patient, nor is there any apparent correlation between clinical phenotype and genetic class.

Cultured FA cells are unusually sensitive to DNA crosslinking agents such as mitomycin C whereas their sensitivity to radiation is close to normal. In the hands of Zakrzewski and Sperling (1982), complementation studies based on mitomycin C sensitivity showed no evidence of heterogeneity when fusion was done between cells from different ethnic groups. Complementation studies with hybrids of cell lines derived from 4 patients in whom different biochemical lesions had been postulated led Zakrzewski et al. (1983) to conclude that the mutations are allelic.

Heterogeneous responses of various cell lines to DNA crosslinking treatments suggest genetic heterogeneity (Moustacchi and Diatloff-Zito, 1985), as do complementation studies (see 300514). Diatloff-Zito et al. (1986) found that normal DNA transfected into FA cells rendered the cells resistant to the effects of mitomycin C. Transfection of DNA of their own cells or DNA of yeast or salmon sperm did not give resistance.

Shaham et al. (1987) likewise found by transfection experiments that DNA sequences present in both the human and the Chinese hamster will correct the 2 cellular defects that are hallmarks of FA: spontaneous chromosome breakage and hypersensitivity to the cell-killing and clastogenic effects of the difunctional alkylating agent diepoxybutane. These observations opened the way for cloning 'the FA gene,' mapping it, and determining its gene product and precise function. Chaganti and Houldsworth (1991) gave a review.

Strathdee et al. (1992) suggested that there are at least 4 different FA genes, mutations at any one of which can lead to the FA phenotype.

Auerbach (1992) suggested that the cellular defect in FA results in chromosomal instability, hypersensitivity to DNA damage, and hypermutability for allele-loss mutations, thus predisposing to leukemia as a multistep process. Auerbach (1992) pointed to topoisomerase I (TOP1; 126420) and proliferating cell nuclear antigen (PCNA; 176740) as candidate genes for FA of complementation group A because of their location on chromosome 20 as well as their known function. Saito et al. (1994) performed a mutation analysis on topoisomerase I cDNA from FA cells by using chemical cleavage mismatch scanning and nucleotide sequencing. No mutation was detected from GM1309, an FA cell line of group A.

Levran et al. (1997) used SSCP analysis to screen genomic DNA from a panel of 97 racially and ethnically diverse FA patients from the International Fanconi Anemia Registry for mutations in the FAA gene (607139). A total of 85 variant bands were detected. Forty-five of the variants were probably benign polymorphisms and forty variants were considered probable pathogenic mutations.

Wijker et al. (1999) investigated the molecular pathology of Fanconi anemia by screening the FAA gene for mutations in a panel of 90 patients identified by the European FA research group, EUFAR. A highly heterogeneous spectrum of mutations were identified, with 31 different mutations being detected in 34 patients. The mutations were scattered throughout the gene, and most were predicted to result in the absence of the FAA protein. The heterogeneity of the mutation spectrum and the frequency of intragenic deletions present a considerable challenge for the molecular diagnosis of FA.

Joenje and Patel (2001) reviewed the molecular basis of Fanconi anemia. They referred to Fanconi anemia, xeroderma pigmentosum (see 278700), and hereditary nonpolyposis colorectal cancer (see 120435), all of which feature genomic instability in combination with a strong predisposition to cancer, as 'caretaker-gene diseases.' The common feature of these disorders is an impaired capacity to maintain genomic integrity, which results in the accelerated accumulation of key genetic changes that promote cellular transformation and neoplasia. Cancer predisposition in these diseases is therefore an indirect result of the primary genetic defect. Grompe and D'Andrea (2001) reviewed the molecular genetics of FA and noted the presumed interaction of BRCA1 with the 8 FA complementation group proteins in a model of interstrand crosslink repair.

D'Andrea (2003) reviewed studies indicating that disruption of the FA/BRCA pathway, by germline mutations, somatic mutations, or epigenetic silencing of FA genes, may contribute to epithelial cancer progression.

Soulier et al. (2005) found that 8 (15%) of 53 patients with Fanconi anemia had spontaneous genetic reversion correcting the FA mutations. Immunoblot analysis of peripheral blood cells from all 8 revertant patients detected FANCD2 monoubiquitination, illustrating that the FA/BRCA pathway was intact in these cells. In contrast, fibroblasts from 6 of the 8 revertants showed abnormal FANCD2 patterns, indicating functional FA reversion in the peripheral blood cells. The 2 remaining revertants had positive chromosomal breakage tests, suggesting somatic mosaicism. Genetic reversion was associated with higher blood counts and with clinical stability or improvement.

In cell lines derived from 2 sibs originally reported by Meetei et al. (2005) as having FANCM due to biallelic mutations in the FAAP250 gene (FANCM; 609644), Singh et al. (2009) identified biallelic mutations in the FANCA gene (607139.0011 and 607139.0012). Singh et al. (2009) noted that only 1 of the sibs had clinical features of the disorder and that the clinically affected sib carried only 1 FANCM mutation. The clinically unaffected sib (EUFA867) carried both biallelic FANCA mutations and biallelic FANCM variants (609644.0001 and 609644.0002). Singh et al. (2009) reclassified the affected sib as having FANCA, and suggested that FANCM deficiency in the unaffected sib may have overruled the FANCA defect and changed the clinical outcome, possibly even attenuating the phenotype.

By exome sequencing in a 43-year-old infertile Spanish man (patient 04-170) with nonobstructive azoospermia and Sertoli cell-only syndrome (SCO) on testicular biopsy, in whom known causes of azoospermia had been excluded, Krausz et al. (2019) identified homozygosity for a missense mutation in the FANCA gene (R880Q; 607139.0013). His affected brother was also homozygous for the mutation. Screening for FANCA variants in a cohort of 27 additional infertile Spanish men with azoospermia and SCO, who also had a platelet count less than 200,000/L and mean corpuscular volume greater than 85 fL, revealed 1 patient (patient 14-339) who was compound heterozygous for FANCA mutations (607139.0014-607139.0015). The authors suggested that screening for FANCA variants in infertile men with SCO might identify undiagnosed FA patients before the appearance of severe clinical manifestations of the disease.

Exclusion Studies

Schweiger et al. (1987) suggested that the defect in Fanconi anemia is one of impaired ADP-ribosylation. Several independent observations have suggested that ADPRT (173870) might be the site of the mutation in Fanconi anemia; however, Flick et al. (1992) could find no abnormality in cells from an FA patient of complementation group A (cell line GM6914).

Rosendorff and Bernstein (1988) concluded that in vitro enhancement of chromosome breakage by DEB and mitomycin C is usually a reliable technique to identify FA homozygotes but could not be depended on to identify individual FA heterozygotes.

Prenatal Diagnosis

Auerbach et al. (1985) attempted prenatal diagnosis in 30 fetuses at risk, using increased baseline and DEB-induced chromosomal breakage in amniotic fluid cells (and in 4 cases, chorion villus cells) as the measure of affection. Seven of the fetuses were diagnosed as affected; 2 were carried to term and 5 were terminated. The 2 who went to term were clinically affected; 2 of the abortuses showed congenital malformations, including abnormalities of the thumb and radius. No clinical suggestion of FA was found in the other 23 cases with diagnosis of no FA type abnormality.

Auerbach et al. (1986) extended the studies to the first trimester of pregnancy by the study of chromosomal breakage induced by DEB. Baseline chromosomal breakage and breakage after the agent were analyzed in 10 pregnancies: in 2, Fanconi anemia was diagnosed; in 8, FA was excluded even though the fetus was at risk. The results were unambiguous.

Poole et al. (1992) described monozygotic twin girls in whom the diagnosis of Fanconi anemia had been made at birth on the basis of limb anomalies and an apparently increased baseline chromosomal breakage frequency in one twin. Over a 13-year follow-up, they had not developed aplastic anemia or other hematologic manifestations of FA. Furthermore, repeat studies in 2 laboratories showed no evidence for increased baseline or DEB-induced chromosomal breakage in either twin. Using the scoring system for FA diagnosis developed by Auerbach et al. (1989), an FA probability coefficient of 0.98 was obtained. Through the International FA Registry, 15 additional patients were identified who had an FA probability score of 0.75 or greater but who had not developed aplastic anemia and were DEB negative. Poole et al. (1992) suggested that these patients should not be considered as instances of FA and that they probably represent a heterogeneous group of disorders with genetic as well as nongenetic causes such as Holt-Oram syndrome (142900), VATER and VACTERL association (192350), and IVIC syndrome (147750).

Deeg et al. (1983) performed allogeneic marrow transplantation in 8 patients with Fanconi anemia. Seven were pretreated with cyclophosphamide alone and one with that agent plus procarbazine and antithymocyte globulin. All had engraftment. Three died of graft-versus-host disease (GVHD; see 614395) and one of cerebral hemorrhage. Four were surviving 647 to 3,435 days after grafting. Two were well; 2 had chronic GVHD that was improving.

Porfirio et al. (1989) found that the iron chelator desferrioxamine (DFO) partially corrected the chromosome instability in Fanconi anemia. The study was undertaken on the assumption that one of the mechanisms involved in the pathogenesis of Fanconi anemia may be impaired capacity of the cells to remove active oxygen species. There appears to be a relationship between intraleukocyte chelatable iron pool and free radical formation. Porfirio et al. (1989) concluded that it is tempting to envisage a therapeutic trial with DFO.

Gluckman et al. (1989) achieved hematopoietic reconstitution in a 5-year-old boy with severe Fanconi anemia by administration of cryopreserved umbilical cord blood from a sister shown by prenatal testing to be unaffected by the disorder, to have a normal karyotype, and to be HLA-identical to the patient. They used a pretransplantation conditioning procedure developed specifically for the treatment of such patients. This technique makes use of the hypersensitivity of the abnormal cells to alkylating agents that crosslink DNA and to irradiation. Broxmeyer et al. (1989) had proposed that cord blood might be useful for such hematopoietic reconstitution.

Gluckman et al. (1992) gave a preliminary report on results of allogeneic bone marrow transplants (BMT) based on the records of the International Bone Marrow Transplant Registry. They suggested that because of the good results of BMT, the adverse effect of previous blood transfusions, the possible toxicity of long-term, high-dose androgen therapy, and the risk of leukemic transformation, it seemed advisable to transplant all patients with an HLA-identical sib as soon as pancytopenia requiring androgen therapy developed. Kohli-Kumar et al. (1994) reported results with bone marrow transplantation from matched sibs in 18 patients.

The findings of clastogenic factor in plasma from patients with Fanconi anemia by Emerit et al. (1995) has possible therapeutic implications. As had previously been reported for ataxia-telangiectasia and Bloom syndrome, transferable clastogenic material could be demonstrated in the plasma from patients with Fanconi anemia. While all plasma ultrafiltrates from homozygotes had chromosome damaging properties, the clastogenic material had to be concentrated in most heterozygotes to reach detectable levels. The clastogenic effect was exerted via the intermediacy of superoxide radicals, since it was regularly inhibited by superoxide dismutase. This added further evidence for a prooxidant state in Fanconi anemia. The clastogenic activity possibly plays a role in the progressive impairment of blood cell-producing bone marrow and may predispose patients to develop cancer and leukemia. Prophylactic use of antioxidants may be recommended, using clastogenic plasma activity as a guide.

Rackoff et al. (1996) reported that prolonged administration of granulocyte colony stimulating factor (GCSF; 138970) exerts a stimulatory effect on the bone marrow of Fanconi anemia patients and may be used to maintain a clinically adequate absolute neutrophil count in these patients. In some patients GCSF had beneficial effects on multiple hematopoietic lineages and may be used in combination with cytokine protocols for patients with progressive aplastic anemia. Rackoff et al. (1996) also reported that GCSF increases the number of circulating CD34 cells in Fanconi anemia patients.

The bone marrow failure associated with Fanconi anemia can be cured by successful allogeneic hematopoietic stem cell (HSC) transplantation. However, with donors other than HLA-identical sibs, this approach is associated with high morbidity and poor survival. Therefore, Grewal et al. (2004) used preimplantation genetic diagnosis (PGD) to select an embryo produced by in vitro fertilization (IVF) that was unaffected by FA and was HLA-identical to the proband. The patient was a 6-year-old girl with FA and myelodysplasia previously treated with oxymetholone and prednisone. After her parents underwent 5 cycles of IVF with intrauterine transfer of 7 embryos over a span of 4 years, successful pregnancy ensued. Twenty-eight days after delivery, the patient underwent transplantation with her newborn sib donor's HLA-identical umbilical cord blood HSCs. Neutrophil recovery occurred on day 17 without subsequent acute or chronic graft-versus-host disease. At the time of report, 2.5 years after transplantation, the patient was well and hematopoiesis was normal. This was said to be the first described successful transplantation, using IVF and PGD, of HSCs from a donor selected on the basis of a specific disorder and HLA characteristics. Grewal et al. (2004) discussed the medical, legal, and ethical issues involved.

Farrell et al. (1994) reviewed a patient originally diagnosed by Lewis et al. (1991) with Baller-Gerold syndrome (218600) and changed the diagnosis to Fanconi anemia on the basis of the finding of chronic thrombocytopenia. The pattern of anomalies included bilateral radial ray defects, right renal dysplasia, ventricular septal defect, anteriorly placed anus, persistent cloaca, and congenital hydrocephalus. Diepoxybutane (DEB) chromosome testing in 2 laboratories showed an elevated rate of mean chromosome breaks per cell consistent with that diagnosis. Farrell et al. (1994) pointed out that VACTERL with hydrocephalus (276950) has also been shown to represent Fanconi anemia on the basis of chromosome breakage studies.

Rossbach et al. (1996) described 2 brothers with presumed Baller-Gerold syndrome, one of whom had previously been diagnosed with the association of vertebral, cardiac, renal and limb anomalies, anal atresia, and tracheoesophageal fistula (VACTERL) with hydrocephalus, who were evaluated for chromosome breakage because of severe thrombocytopenia in one of them. Spontaneous and clastogen-induced breakage was markedly increased in both patients as compared to controls. Clinical manifestations and chromosome breakage consistent with Fanconi anemia had been reported earlier in patients with a prior diagnosis of Baller-Gerold syndrome by Farrell et al. (1994) and in 3 patients with the VACTERL association with hydrocephalus by Toriello et al. (1991) and Porteous et al. (1992). The authors commented that the observations underscore the clinical heterogeneity of Fanconi anemia and raise the question of whether these syndromes are distinct disorders or phenotypic variants of the same disorder.

Raya et al. (2009) showed that, on correction of the genetic defect, somatic cells from Fanconi anemia patients can be reprogrammed to pluripotency to generate patient-specific induced PS (iPS) cells. These cell lines appear indistinguishable from human embryonic stem cells and iPS cells from healthy individuals. Most importantly, Raya et al. (2009) demonstrated that corrected Fanconi anemia-specific iPS cells can give rise to hematopoietic progenitors of the myeloid and erythroid lineages that are phenotypically normal, i.e., disease-free. Raya et al. (2009) concluded that their data offered proof of concept that iPS cell technology can be used for the generation of disease-corrected, patient-specific cells with potential value for cell therapy applications. Raya et al. (2009) were able to induce iPS cells from 3 FA patients, 2 from the FA-A complementation group and 1 from the FA-D2 complementation group.

Joenje and Patel (2001) stated that Fanconi anemia has a general, worldwide prevalence of 1-5 per million and is found in all races and ethnic groups, with an estimated heterozygous mutation carrier frequency of between 0.3 and 1%.

Rosendorff et al. (1987) estimated that the birth incidence of FA in white, Afrikaans-speaking South Africans is at least 1 in 22,000, the calculated heterozygote prevalence being approximately 1 in 77. They attributed this unusually high gene frequency to founder effect. Founder effect was strongly supported by the demonstration of allelic association between the disease and marker D16S303 in the Afrikaner population (Pronk et al., 1995). Alter (1992) concluded that Fanconi anemia in the Afrikaners represents the most clearly differentiated form of this heterogeneous disorder. She concluded that Fanconi anemia in blacks is clinically indistinguishable from that in other groups with the exception of the Afrikaners.

On the basis of complementation analysis of 47 FA patients from Europe and U.S./Canada, the following frequencies of the various subtypes were identified by Buchwald (1995): 31 were group A (66%), 2 were group B (4.3%), 6 were group C (12.7%), 2 were group D (4.3%), and 6 were group E (12.7%). The above data were compiled from several reports. Reporting for the European Fanconi Anaemia Research Group, Joenje (1996) found that among ethnically and clinically unselected FA patients from Germany and the Netherlands, FA-A was most prevalent in Germany (13/22, 59%), whereas in the Netherlands a majority of patients were FA-C (4/6, 67%).

Jakobs et al. (1997) determined the complementation group represented by each of 16 unrelated FA patients from North America. The majority of the patients belonged to FA complementation group A (69%), followed by FA-C (18%), FA-D (4%), and FA-B or FA-E (9%).

Savoia et al. (1996) found that 11 of 12 Fanconi anemia patients analyzed by complementation belonged to complementation group A. Four and 7 families came from 2 geographic clusters in the Veneto and Campania regions, respectively, which are thought to consist of aggregates of related families in reproductive isolation. The clinical characteristics of the patients showed both intra- and interfamilial heterogeneity, although overall the disease had a relatively mild course. Since the populations of both regions are likely to represent genetic isolates, the findings of Savoia et al. (1996) predicted linkage disequilibrium for markers flanking the FAA gene on chromosome 16. Thus, they concluded that DNAs from these FA families may be useful for positional cloning of the gene through haplotype disequilibrium mapping.

Tipping et al. (2001) genotyped 26 Fanconi anemia families of the Afrikaner population of South Africa using microsatellite and single-nucleotide polymorphic markers and detected 5 FANCA haplotypes. Mutation scanning of the FANCA gene revealed association of these haplotypes with 4 different mutations. The most common was an intragenic deletion of exons 12-31 (607139.0007), accounting for approximately 60% of FA chromosomes in 46 unrelated Afrikaner FA patients, while 2 other mutations accounted for approximately 20%. Screening for these mutations in the European populations ancestral to the Afrikaners detected 1 patient from the western Ruhr region of Germany who was heterozygous for the major deletion. The mutation was associated with the same unique FANCA haplotype as in Afrikaner patients. Genealogic investigation of 12 Afrikaner families with FA revealed that all were descended from a French Huguenot couple who arrived at the Cape on June 5, 1688; mutation analysis showed that the carriers of the major mutation were descendants of this same couple. The molecular and genealogic evidence is consistent with transmission of the major mutation to western Germany and the Cape near the end of the 17th century, confirming the existence of a founder effect for FA in South Africa.

In a retrospective study of 145 FA patients from North America, Rosenberg et al. (2003) reported that 9 developed leukemia and 14 developed a total of 18 solid tumors. The ratio of observed to expected cancers was 50 for all cancers, 48 for all solid tumors, and 785 for leukemia. The highest ratio of observed to expected solid tumors was 4,317 for vulvar cancer, 2,362 for esophageal cancer, and 706 for head and neck cancer.

Kutler et al. (2003) analyzed clinical data from 754 FA patients from North America enrolled in the International Fanconi Anemia Registry, of whom 601 (80%) experienced the onset of bone marrow failure and 173 (23%) had a total of 199 neoplasms. One hundred and twenty (60%) of the neoplasms were hematologic and 79 (40%) were nonhematologic. The risk of developing bone marrow failure and hematologic and nonhematologic neoplasms increased with advancing age, such that by 40 years of age, cumulative incidences were 90%, 33%, and 28%, respectively. Univariate analysis revealed a significantly earlier onset of bone marrow failure and poorer survival for complementation group C compared with groups A and G; however, there was no significant difference in the time of hematologic or nonhematologic neoplasm development between these groups.

Levitus et al. (2004) tabulated 11 genetic subtypes of Fanconi anemia, giving a pie diagram of the relative prevalences of the complementation groups based on the first 241 FA families classified by the European Fanconi Anemia Research Programme, 1994-2003.

In a review, Alter (1992) pointed out that Fanconi anemia should really be called Fanconi syndrome because the primary defect or defects are not hematopoietic, dermatologic, or orthopedic, but presumably related in some manner to DNA repair. However, the designation Fanconi syndrome was already used to describe a specific constellation of renal tubular dysfunction.

Joenje et al. (2000) suggested that future assignments of patients with FA to new complementation groups should conform with stringent criteria. A new group should be based on at least 2 patients