Ichthyosis, X-Linked

A number sign (#) is used with this entry because X-linked ichthyosis (XLI), which results from steroid sulfatase deficiency, is caused by mutation or deletion of the STS gene (300747) on chromosome Xp22. Most patients (90%) have deletions of the STS gene.

Some patients have larger deletions at Xp22.3 that encompass neighboring genes. These patients may present with mental retardation, Kallmann syndrome (KAL1; 308700), which comprises hypogonadotrophic hypogonadism and anosmia, features of X-linked chondrodysplasia punctata (CDPX1; 302950), short stature (SHOX; 312865), and/or ocular albinism (OA1; 300500) in addition to X-linked ichthyosis. These complicated forms of XLI thus represent contiguous gene deletion syndromes (Ballabio et al., 1989; Cuevas-Covarrubias and Gonzalez-Huerta, 2008).

Description

X-linked ichthyosis is clinically characterized by widespread, dark brown, polygonal scales and generalized dryness. Cutaneous manifestations are present soon after birth and usually do not improve with age. The histopathology of XLI typically shows compact hyperkeratosis and slight acanthosis with a normal granular layer (summary by Takeichi and Akiyama, 2016).

X-linked ichthyosis is fundamentally the same disorder as placental steroid sulfatase deficiency, which is often first noted in the pregnant mother of affected males by decreased estrogen or delayed progression of parturition (Alperin and Shapiro, 1997). This is thus an example of affinity ('lumping') of phenotypes thought previously to be separate, the opposite of genetic heterogeneity.

Schnyder (1970) gave a useful classification of the inherited ichthyoses.

Hernandez-Martin et al. (1999) provided a comprehensive review of X-linked ichthyosis. They pointed out that among all genetic disorders X-linked ichthyosis shows one of the highest ratios of chromosomal deletions; complete deletion has been found in up to 90% of patients.

Takeichi and Akiyama (2016) reviewed inherited nonsyndromic forms of ichthyosis.

Clinical Features

Csorsz (1928) reported a Hungarian family with X-linked ichthyosis. There were 2 affected females who were presumed to be homozygous. Schlammadinger et al. (1987) restudied the Hungarian family reported by Csorsz (1928). A female member of the family who as a child was described as having ichthyosis was found on restudy to have no sign of the disorder and was determined to be heterozygous by enzyme studies. A second affected female, presumably homozygous, was apparently not investigated by enzyme levels. No pregnancy-related complications, hypogenitalism, cryptorchidism, or deep corneal opacities were found in the family.

Orel (1929) found reports of 10 families with the X-linked form of ichthyosis in the literature.

Wells and Jennings (1967) reported that onset of the X-linked form of ichthyosis was at birth, and that the scalp, ears, neck, and some of the flexures were involved. There was more striking scaling on the abdomen than on the back, as well as scaling down the front of the leg onto the dorsum of the foot.

Sever et al. (1968) described deep corneal opacities in all of 17 males with X-linked ichthyosis. There were no overt symptoms. Jay et al. (1968) found ocular opacities as a late feature of X-linked ichthyosis including the carrier state; in their series, all patients over 25 years, but only 5 of 8 patients under 25, showed this abnormality.

Went et al. (1969) reported a large Dutch kindred with X-linked ichthyosis spanning 7 generations. None of those affected had obvious symptoms at birth, but developed scaling of the skin soon after or during the first year of life. The lesions were symmetrical and affected anterior and posterior surfaces of the upper and lower extremities, scalp, and trunk. Almost all patients had no involvement of the flexure areas, palms, or soles. The scales were black or gray in about half of patients, and white in the other half. All affected individuals reported improvement of the lesions during the summer.

Jobsis et al. (1976) was the first to publish the association between X-linked ichthyosis and steroid sulfatase deficiency.

Koppe et al. (1977, 1978) reported 3 pregnant women with decreased urinary estrogen secretion who gave birth to 3 boys that later developed ichthyosis at ages 2 to 8 months. The placenta in each case had decreased steroid sulfatase activity, which was also demonstrated in the skin of all 3 affected boys. Two of the families had a history consistent with X-linked recessive inheritance. Koppe et al. (1977, 1978) concluded that the sulfatase deficiency was a factor in the skin disorder.

France and Liggins (1969) reported a family from New Zealand in which several women had low estrogen production during pregnancy resulting from placental steroid sulfatase deficiency. The disorder was manifest clinically by delay in the onset of labor and relative refractoriness to oxytoxic agents. France and Downey (1974) showed that the deficiency was limited to the placenta; the mother did not show deficiency in her tissues. All affected pregnancies were males. Shapiro et al. (1978) reported that several male members of the family with placental steroid sulfatase deficiency reported by France and Liggins (1969) developed ichthyosis in the first months of life. Most had normal-appearing skin at birth. The trunk and extensor surfaces of the extremities were the most involved. One patient had deep corneal opacities found by slit-lamp examination. Noting that normal skin has sulfatase activity, Shapiro et al. (1978) postulated that the skin disorder in this family resulted from steroid-sulfatase deficiency. In a follow-up study, Shapiro et al. (1978) found decreased steroid sulfatase activity in fibroblasts isolated from 25 individuals with X-linked ichthyosis from 4 countries. Controls and patients with other forms of ichthyosis did not have decreased enzyme levels. Shapiro et al. (1978) stated that they knew of no patient with X-linked ichthyosis that did not have this specific enzyme defect, and concluded that the disorder results in the skin disease postnatally in affected males. The authors concluded that X-linked ichthyosis results from a common mutation affecting steroid sulfatase activity.

Macsai and Doshi (1994) described a 73-year-old man with X-linked ichthyosis and steroid sulfatase deficiency in whom superficial corneal opacities were found. The opacities were granular in nature, involving the subepithelial and anterior stromal layers.

Heterozygous Females

Sever et al. (1968) described deep corneal opacities in 7 of 8 heterozygous females. There were no overt symptoms.

Went et al. (1969) reported mild abnormalities of the skin in about one-fourth of obligate heterozygous females of a large Dutch kindred with X-linked ichthyosis.

Solomon and Schoen (1971) reported a patient with XO Turner syndrome and ichthyosis, the latter of which was shown to be X-linked by pedigree and clinical features.

Other Features

Traupe and Happle (1983) found 7 instances of cryptorchidism in a series of 25 patients with STS deficiency and suggested a causal relationship.

Lykkesfeldt et al. (1983) reported 2 men with STS deficiency and testicular cancer. One patient had the left testis removed for seminoma at age 21 and the right testis removed for embryonal cancer at age 26. The second had the left testis removed for seminoma at age 31. Both had normally descended testes, but a nephew of the second patient had STS deficiency, ichthyosis, and bilateral inguinal cryptorchidism. The authors noted that the testis has potent STS activity and may have a role in gonadal steroid regulation.

Lykkesfeldt et al. (1985) studied 76 cases in 50 kindreds; 42 kindreds had multiple cases. Maldescent of the testes was noted in 9 patients. Testicular cancer occurred in 2 males with normally descended testes. Corneal opacities, not impairing visual acuity, were seen in 14 of 28 males by slit-lamp examination.

Garcia Perez and Crespo (1981) and Stoll et al. (1983) reported 2 families containing 5 boys with the combination of hypertrophic pyloric stenosis and X-linked recessive ichthyosis.

Biochemical Features

Hameister et al. (1979) reported 3 independent pregnancies with partial deficiency of placental steroid sulfatase associated with low estriol excretion and failure of labor induction. In all 3 cases, a male was delivered and diagnosis was confirmed enzymatically in placenta homogenates. In 1 case, fibroblasts from the son showed steroid sulfatase that was 34% of normal, whereas the mother had normal values. None of the cases had developed ichthyosis by the age of 6 months.

Epstein et al. (1981) found that low density lipoproteins from patients with X-linked ichthyosis have abnormally rapid anodic electrophoretic mobility. The finding was explained by increased plasma cholesterol sulfate concentration, which is found predominantly in the low density lipoprotein fraction of plasma.

Diagnosis

Shapiro et al. (1978) identified placental steroid sulfatase deficiency by measuring estriol in the urine of pregnant women as an indication of a gestational abnormality.

Lake et al. (1991) developed a histochemical method for demonstration of hexanol dehydrogenase activity by use of a simple staining method on cryostat sections of skin biopsies as an adjunct to the biochemical assay in the differentiation of the various forms of ichthyosis.

Shapiro (1997) noted that the detection of STS deficiency, which may have a frequency of 1 in 3,000 males, has increased greatly by routine use of screening of estrogen metabolism in pregnancy.

Clinical Management

In a prospective half-side trial, Lykkesfeldt and Hoyer (1983) found that a topical cream containing 10% cholesterol effected considerable improvement, suggesting that reduction in the cholesterol content of the stratum corneum may be responsible for abnormal cornification in this disorder.

Gene Therapy

Freiberg et al. (1997) used X-linked ichthyosis to develop a model of corrective gene therapy to human skin in vivo. They produced a retroviral expression vector and used it for STS gene transfer to primary keratinocytes in patients with this disorder. Transduction was associated with restoration of full-length STS protein expression as well as steroid sulfatase activity in proportion to the number of proviral integrations in XLI cells. Transduced and uncorrected XLI keratinocytes, along with normal controls, were then grafted onto immunodeficient mice to regenerate full thickness human epidermis. Unmodified XLI keratinocytes regenerated a hyperkeratotic epidermis lacking STS expression with defective skin barrier function, effectively recapitulating the human disease in vivo. Transduced XLI keratinocytes from the same patients, however, regenerated epidermis histologically indistinguishable from that formed by keratinocytes from patients with normal skin. Transduced XLI epidermis demonstrated STS expression in vivo by immunostaining, as well as a normalization of histologic appearance at 5 weeks post-grafting. In addition, transduced XLI epidermis demonstrated a return of barrier function parameters to normal.

Pathogenesis

Elias et al. (1984) concluded that accumulation of undegraded cholesterol sulfate is responsible for scale-formation in steroid sulfatase deficiency.

Shapiro (1997) noted that ichthyosis with STS deficiency is related to increased water loss in the skin with resulting desiccation. Ichthyosis occurs with other disorders of lipid metabolism in the skin, including Refsum disease (266500) and Sjogren-Larsson syndrome (270200).

Zettersten et al. (1998) investigated the significance of the fact that patients with X-linked ichthyosis display a 10-fold increase in cholesterol sulfate in squamous keratinizing epithelia, as well as a 50% reduction in cholesterol. They found that patients with this disorder displayed both an abnormal barrier under basal conditions and a delay in barrier recovery after acute perturbation. Moreover, both the functional and the structural abnormalities were corrected by topical cholesterol. However, topical cholesterol sulfate produced both a barrier abnormality in intact skin and extracellular abnormalities in isolated stratum corneum, effects largely reversed by coapplications of cholesterol. These results suggested that cholesterol sulfate accumulation rather than cholesterol deficiency is responsible for the barrier abnormality.

Mapping

Kerr et al. (1964) presented evidence suggesting that the X-linked ichthyosis locus may be within 'mappable' distance of the Xg locus (314700). Closer situation of the Xg and ichthyosis loci was indicated by studies of Adam et al. (1969) who estimated the recombination fraction as 0.105 and of Went et al. (1969) who found a value of 0.115. Close linkage with the deutan colorblindness (303800), protan colorblindness (303900) and G6PD (305900) loci was excluded (Filippi and Meera Khan, 1968; Adam et al., 1969).

Tiepolo et al. (1980) found steroid sulfatase to be severely deficient in a boy with ichthyosis and nullisomy for the distal portion of Xp; the mother, who was monosomic for this segment, had steroid sulfatase levels in the heterozygous range. Muller et al. (1981) used deletion mapping to assign the steroid sulfatase locus to Xp22.3; they found almost undetectable levels of the enzyme in 2 brothers with the same defect as in the patient of Tiepolo et al. (1980) and levels like those of heterozygotes in the mother.

Wieacker et al. (1983) studied the linkage between RC8 (DXS9) on Xp22.3-p21 and X-linked ichthyosis. At least 2 crossovers were found among 9 meioses in an informative family, suggesting that the 2 loci were about 25 cM apart. Since STS is 15 cM proximal to the Xg locus and since the RC8 and Duchenne muscular dystrophy loci (DMD; 310200) are closely linked, DMD may be 50 cM or more from Xg.

Ballabio et al. (1986) reported an Italian family in which 5 males had X-linked ichthyosis associated with STS deficiency as well as hypogonadotropic hypogonadism and anosmia, consistent with Kallmann syndrome. Linkage analysis suggested linkage between STS deficiency and X-linked Kallmann syndrome.

Shapiro (1987) suggested that the STS locus must be very close to the pseudoautosomal segment of Xp. The STS locus was usually deleted in XX males in whom TDF (480000) was presumably translocated to the end of Xp. Shapiro (1987) suggested that anomalous exchange between the X and Y chromosomes may account for a high frequency of X-linked ichthyosis, about 1 in 5,000 in many populations.

Gillard et al. (1987) used a RFLP closely linked to STS to demonstrate deletion of the STS locus at Xpter-p22.3 in 8 of 9 families with X-linked ichthyosis. In an extension of these studies, Gillard et al. (1987) found deletion of a DNA marker tightly linked to STS in affected males in 12 of 15 families with X-linked ichthyosis. The findings suggested that a high proportion of the mutations at the STS locus leading to enzyme deficiency are deletions, presumably generated by unequal crossover events in female meiosis or by illegitimate X-Y interchange in male meiosis.

Wirth et al. (1988) used polymorphic DNA markers from distal Xp to examine 9 unrelated families with X-linked ichthyosis. Close linkage was found between the disease locus and the markers DXS16, DXS89, and DXS143. In 8 families, Southern hybridization with the human steroid sulfatase cDNA and GMGX9 probes showed a deletion of corresponding loci in affected males. Three patients in the ninth family had no evident deletion when studied with 2 probes.

Cytogenetics

Complicated X-Linked Ichthyosis Due to Contiguous Gene Deletion Syndrome

Metaxotou et al. (1983) described a 14-year-old boy with X-linked ichthyosis associated with nullisomy for the Xpter-p22 segment and a translocation t(X;Y)(p22;q11). The boy also had mental retardation and hypogonadism. The mother was monosomic for the deleted segment of Xp and had the same X;Y translocation.

Traupe et al. (1984) described a typical instance of X-linked ichthyosis in which the patient also had severe hypogenitalism and hypogonadism. Delivery was protracted. The patient had an affected maternal first cousin, and the maternal grandfather of the 2 affected males was affected.

Curry et al. (1984) reported 2 families in which affected males had X-linked chondrodysplasia punctata, nasal hypoplasia, ichthyosis, and mental retardation associated with an inherited deletion of Xp22.32. Biochemical studies suggested a deletion of the STS gene, Xg, and the M1C2X locus. The women carrying the Xp deletion had normal gonadal function and fertility, but were shorter than the noncarriers in their families (P less than 0.00001). These findings indicated that small cytogenetic abnormalities may account for the cosegregation of several disorders with mendelian patterns of inheritance.

Ross et al. (1985) described a family in which 4 brothers had X-linked ichthyosis, mental retardation, and short stature associated with nullisomy for Xpter-p22.3 resulting from an Xp to Yq translocation with the entire Y short arm and deletion of Xpter-p22.3: 46,Y,t(x;y)(Xqter-p22.3::Yq11-qter). Cultured cells were completely deficient in steroid sulfatase.

Sunohara et al. (1986) described a family in which 3 men had ichthyosis, anosmia, hypogonadotropic hypogonadism, nystagmus with decreased visual acuity, strabismus, hypopigmentation of the iris, and mirror movements of the hands and feet. Two of them had limitation of ocular movement and unilateral renal agenesis or hypoplasia. Inheritance appeared to be X-linked recessive. Steroid sulfatase and arylsulfatase C activities in leukocytes and fibroblasts were markedly diminished. Karyotype was normal.

Ballabio et al. (1986) reported an Italian family in which 5 males had X-linked ichthyosis associated with STS deficiency and hypogonadotropic hypogonadism. The pregnancies were complicated by prolonged labor, necessitating C-section in 3 patients. All had the classic skin lesions, as well as variable features including micropenis, small testes, and cryptorchidism. All also had some form of anosmia, consistent with Kallmann syndrome. These families and the family reported by Andria et al. (1984) were postulated to have a microdeletion of Xp chromosome involving both the STS gene and the gene responsible for X-linked Kallmann syndrome. Linkage studies in 1 of their families showed no crossing over with a probe that maps to Xpter-p22, suggesting that the disease locus was indeed in that area. Ballabio et al. (1986) noted that the patients described by Sunohara et al. (1986) showed peculiar manifestations that have been reported in patients with Kallmann syndrome, including renal agenesis and neurologic disorders such as mirror movements.

Shapiro and Yen (1987) responded to the suggestion that the condition in these patients may represent a microcytogenetic disorder (Schmickel, 1986). They stated that homologous but nonfunctional sequences of STS were found on the long arm of the Y chromosome in the patients of Sunohara et al. (1986). Indeed, they found a complete deletion of the STS gene with continued presence of MIC2 (313470) sequences, which are located more distally on the X chromosome, in both the X and Y chromosomes. In studies of 9 unrelated patients with simple X-linked ichthyosis, they found 7 with complete deletion of the STS gene and 1 with a partial 5-prime deletion. Only 1 subject had an intact STS gene.

Ballabio et al. (1988) described a family in which an X/Y translocation t(X;Y)(p22;q11) was transmitted through females in at least 3 generations. Two male first-cousins who had the translocation had X-linked ichthyosis as well as mental retardation. Both deliveries were protracted. One of the boys had features of X-linked chondrodysplasia punctata. STS activity in fibroblasts was profoundly decreased. Ballabio et al. (1988) demonstrated that the translocated region of the Y chromosome included STS; the X/Y translocation may have thus been derived from a recombination event between homologous regions located on the Xp chromosome and the long arm of the Y chromosome. They pointed out that all cases of X/Y translocation involving the STS gene showed mental retardation, whereas patients without mental retardation with X/Y translocation did not have involvement of the STS gene. Their review of families with X/Y translocations, including the family reported by them, showed 24 affected persons in 30 informative meioses. This suggested preferential fertilization of the oocyte carrying the aberrant X chromosome.

Pike et al. (1989) described X-linked ichthyosis and hypogonadism in males in 3 separate sibships connected through females. Endocrinologic testing suggested hypogonadotropic hypogonadism with deficiency of luteinizing hormone.

Gohlke et al. (2000) reported monozygotic male twins with an interstitial deletion of Xp22.3, including the STS gene. The twins had ichthyosis, mental retardation, and epilepsy. Analysis of flanking STS markers narrowed the locus for this phenotype to a region bounded by markers DXS6837 and GS1.

In 4 XLI patients with mental retardation, Van Esch et al. (2005) detected a 1.5-Mb interstitial microdeletion that deleted the VCX3A (300533) and VCX (300229) genes. Array CGH with DNA of an XLI patient with mental retardation and an inherited t(X;Y)(p22.31;q11.2) showed an Xpter deletion of 8.0 Mb resulting in the deletion of all 4 VCX genes and duplication of both VCY (400012) homologs. These data supported the role of VCX3A in the occurrence of mental retardation in XLI patients. Van Esch et al. (2005) proposed a VCX/VCY teamwork-dependent mechanism for the incidence of mental impairment in XLI patients.

Lesca et al. (2005) reported a family in which 7 males had X-linked recessive ichthyosis caused by deletion of Xp22.3, including the VCX3A and VCX genes. Only 1 of the 7 patients had mental retardation. Detailed molecular analysis detected no differences in the deleted chromosomal region between the 1 patient with mental retardation and another with ichthyosis but no mental retardation. Lesca et al. (2005) concluded that VCX3A is not specifically involved in mental retardation.

Among 80 Mexican patients with isolated XLI and normal intelligence, Cuevas-Covarrubias and Gonzalez-Huerta (2008) detected 2 different deletion patterns at the STS locus. One included 62 patients with deletion of STS, VCX3A, and VCX, whereas the other included 18 patients with breakpoints on either side of STS and not including the VCX3A gene. The authors concluded that deletion of VCX3A is not sufficient to result in mental retardation in XLI patients.

Heterogeneity

Munke et al. (1983) documented heterogeneity in the syndrome of ichthyosis and hypogonadism, with STS deficiency in some cases and not in others. See 308200 for a discussion of Rud syndrome, in which ichthyosis and hypogonadism are combined with neurologic abnormality.

Traupe et al. (1984) described a presumably isolated case of ichthyosis associated with hypogenitalism and hypogonadism in a Pakistani male. However, STS activity and serum lipoprotein electrophoresis were normal. The disorder was clinically indistinguishable from that of another patient with STS deficiency and hypogonadism.

Robledo et al. (1995) described a Sardinian kindred in which congenital ichthyosis was associated with normal levels of steroid sulfatase and a normal pattern on Southern blot analysis suggesting the presence of an intact STS gene. Although the pedigree pattern was entirely consistent with X-linked recessive inheritance, the ichthyosis was found to segregate independently of genetic polymorphisms detected by probes mapping to Xp22.3, where the STS locus maps. The search for linkage to markers elsewhere on the X chromosome had not been successful. Robledo et al. (1995) concluded that there may be a form of X-linked ichthyosis due to some mechanism other than STS deficiency (see 300001).

Molecular Genetics

In 12 steroid sulfatase-deficient patients, including 8 cases of classic ichthyosis, Ballabio et al. (1987) found deletion of the STS gene using a specific probe. One of the patients had been reported by Ballabio et al. (1986) as having X-linked ichthyosis and Kallmann syndrome. In all cases, karyotype analysis was normal. Bonifas et al. (1987) found gross deletions of genomic DNA containing the STS gene in 14 of 15 probands with X-linked ichthyosis. Yen et al. (1987) identified complete STS gene deletions in 8 of 10 patients with inherited STS deficiency.

Shapiro et al. (1987) reviewed 4 studies with a total of 45 unrelated cases of X-linked ichthyosis; 41 were found to have a deletion.

In 16 men from 10 unrelated Italian families affected with STS deficiency, Ballabio et al. (1987) found no hybridization signal when Southern blotting was done with an STS cDNA probe. The sample included 2 families with a total of 7 cases combining X-linked ichthyosis and Kallmann syndrome.

Basler et al. (1990, 1992) identified 3 different point mutations in the STS gene (300747.0001-300747.0003) in 3 unrelated patients with X-linked ichthyosis. Alperin and Shapiro (1997) identified 3 additional point mutations in the STS gene (300747.0004-300747.0006) in patients with X-linked ichthyosis and reviewed the point mutations reported by Basler et al. (1990, 1992). All 6 mutations were located in a 105-amino acid region of the C-terminal half of the polypeptide. Five of the 6 mutations were missense, whereas 1 resulted in a frameshift and premature protein termination. In vitro functional expression studies showed that all 6 mutants lacked STS enzymatic activity.

Cuevas-Covarrubias et al. (1995) investigated 5 apparently sporadic cases of X-linked recessive ichthyosis and their mothers. None of the XLI patients showed STS activity; 4 mothers had an activity level compatible with the carrier state and only 1 showed a normal level, indicating that her son had a de novo mutation.

Valdes-Flores et al. (2000) reported a patient with X-linked ichthyosis and a partial STS deletion. The deletion included exons 2 through 10 and included 3-prime flanking sequences extending through DXS1131 and DXS1133. Valdes-Flores et al. (2000) noted that this was the fourth patient with partial deletion of the STS gene to be described, and that Nomura et al. (1995) had reported the third patient.

Valdes-Flores et al. (2001) evaluated 12 apparently sporadic cases of males with X-linked ichthyosis and their mothers. All affected males had undetectable levels of STS activity and complete deletion of the STS gene. Evaluation of their mothers showed 9 of 12 with STS activity compatible with that expected for X-linked carriers. These results were corroborated by FISH. One mother who was shown to be a carrier by FISH had STS activity that was classified as normal. The authors recommended including FISH analysis in mothers of apparently sporadic cases, even when they have normal STS activity, to diagnose the carrier state correctly. Since FISH will not detect partial deletions or point mutations, the authors emphasized the importance of confirming the nature of the mutation in the affected individual before testing the mother.

Population Genetics

X-linked recessive ichthyosis occurs in about 1 in 6,000 males studied in various populations (Shapiro et al., 1978).

Animal Model

Eicher (1974) speculated that the 'scurfy' (sf) mutation in the mouse may be homologous to X-linked ichthyosis of man. Buckle et al. (1985) alluded to ichthyosis with male hypogonadism (see 308200) as an entity separate from ichthyosis with steroid sulfatase deficiency and homologous to 'scurfy' in the mouse. From comparative mapping of the X chromosomes of mouse and man, they predicted that this possibly separate human condition may be determined by a mutation on Xp near OTC (300461).

History

For a biographical account of Karoly Csorsz, see Czeizel (1979).