Incontinentia Pigmenti

A number sign (#) is used with this entry because incontinentia pigmenti (IP) is caused by mutation in the IKK-gamma gene (IKBKG; 300248), also called NEMO, on chromosome Xq28.

Description

Familial incontinentia pigmenti (IP) is a genodermatosis that segregates as an X-linked dominant disorder and is usually lethal prenatally in males (The International Incontinentia Pigmenti Consortium, 2000). In affected females it causes highly variable abnormalities of the skin, hair, nails, teeth, eyes, and central nervous system. The prominent skin signs occur in 4 classic cutaneous stages: perinatal inflammatory vesicles, verrucous patches, a distinctive pattern of hyperpigmentation, and dermal scarring. Cells expressing the mutated X chromosome are eliminated selectively around the time of birth, so females with IP exhibit extremely skewed X-inactivation.

Also see hypomelanosis of Ito (300337), which was formerly designated incontinentia pigmenti type I (IP1).

Clinical Features

Incontinentia pigmenti is a disturbance of skin pigmentation sometimes associated with a variety of malformations of the eye, teeth, skeleton, heart, etc. The pigmentary disturbance, an autochthonous tattooing, is evident at or soon after birth and may be preceded by a phase suggesting inflammation in the skin. In the fully developed disease, the skin shows swirling patterns of melanin pigmentation, especially on the trunk, suggesting the appearance of 'marble cake.' Histologically, deposits of melanin pigment are seen in the corium: the designation was based on the idea that the basal layer of the epidermis is 'incontinent' of melanin. Garrod (1906) may have described the first case, a girl with typical pigmentary changes together with mental deficiency and tetraplegia. The cutaneous phenotype has other interesting features, namely, that in the first months of life it has some characteristics of an inflammatory process and that the pigmentary changes usually disappear completely by the age of 20 years. Caffey disease (infantile hyperostosis; 114000) displays a similar behavior, with pronounced signs suggesting an inflammatory process in many bones with subsequent quiescence and in many cases disappearance of all evidence of previous disease.

Kuster and Olbing (1964) reported a mentally retarded woman with incomplete dentition and a history of skin lesions at birth. She had 1 son and 11 daughters. Six of the girls showed incomplete dentition and incontinentia pigmenti. Spallone (1987) examined 7 affected members in a family with a total of 14 affected members in 3 generations. There were many abortions in the family, several of which were identified as male. Spallone (1987) showed that vascular abnormalities of the retina and disorders of the retinal pigment epithelium are the most important ocular lesions.

Landy and Donnai (1993) reviewed the disorder in full. They pointed out that the dermatologic features classically occur in 4 stages, although all stages may not occur and several stages may overlap. Stage 1 is characterized by erythema, vesicles, and pustules; stage 2 by papules, verrucous lesions, and hyperkeratosis; stage 3 by hyperpigmentation; and stage 4 by pallor, atrophy, and scarring. Dystrophy of the nails is frequent but usually mild. Unilateral breast aplasia is a well-recognized but uncommon feature.

Parrish et al. (1996) reviewed the clinical findings in IP2. They also determined the parent of origin of new mutations for this disorder and presented evidence for tissue-specific differences in the activity of normal and mutant IP2 alleles. Parrish et al. (1996) noted that in affected females the most prominent findings occur in the skin, the eye, and the central nervous system. In affected females the disorder may be diagnosed shortly after birth by the presence of a progressive erythematous and vesicular rash, which becomes sequentially verrucous, pigmented, then atrophic and may leave adolescents and adults with areas of linear and reticular hypopigmentation. Cicatricial alopecia, hypodontia, or anodontia may occur and cicatrization of the retina may be present. Parrish et al. (1996) reported that 98% of affected females showed completely skewed patterns of X inactivation in peripheral blood leukocytes. Fibroblast subclones from a biopsy at the boundary of a skin lesion in a newborn IP2 patient revealed that cells with the disease-bearing X chromosome were still present. Parrish et al. (1996) determined the parent of origin in 15 families and reported that paternal new mutations were twice as common as maternal ones.

Roberts et al. (1998) described a woman with IP who had 2 successive term pregnancies: the first, a male infant, was alive and well at 2 years; the second liveborn male had early postnatal distress and died after 1 day. The 33-year-old mother had been diagnosed with IP at age 18 months. In infancy she developed generalized erythema and blisters, which were initially thought to represent an allergic reaction to variola vaccination. She later developed hyperpigmentation in the affected areas, and whenever she developed a fever, she exhibited a papular rash along the pigmented skin, similar to that described by Pfau and Landthaler (1995). The proposita showed residual marbled pigmentation, conical teeth, and thin hair. Her mother also had alopecia, peg teeth, hypodontia, and eye abnormalities, and had lost 2 male infants around the time of birth. Analysis of polymorphic microsatellite markers, closely linked to the IP gene on Xq28, indicated that each son of the proposita inherited a different X chromosome from his mother. Judging from the findings in the son who died, Roberts et al. (1998) proposed that the neonatal phenotype of IP may be characterized by lethal disturbances in the hematopoietic and immunologic systems.

Late recurrences of the first-stage inflammatory lesions after the initial rash are uncommon and the mechanism involved in this phenomenon is unclear. Bodak et al. (2003) reported 5 cases of children who experienced episodes of late reactivation of IP. In all cases, the recurrences occurred on the previously hyperpigmented streaks several months or years after resolution of the initial eruptions. In most cases, the recurrences were preceded by an infectious episode. Bodak et al. (2003) proposed that reactivation of IP skin lesions is due to the persistence of mutant NEMO keratinocytes in sites of previous lesions. They hypothesized that cytokines, such as TNFA (191160), induce remaining populations of mutant keratinocytes to undergo apoptosis, resulting in the bullous and verrucous lesions characteristic of first-stage inflammatory IP lesions.

O'Doherty et al. (2011) studied 11 patients with IP and found that 5 (47%) had visually significant ocular findings. Minimal retinal findings included straightening of retinal vessels and retinal pigment epithelial changes. Moderate retinal changes included abnormal vascular pattern such as shunt vessels, neovascularization, and ischemia, and severe retinal changes signified retinal detachment. Six of 22 eyes were lost to retinal detachment. The retinal detachments often occurred early in life. O'Doherty et al. (2011) recommended fluorescein angiography (FA) to diagnose ischemic retina in all patients with retinal changes, and early treatment with peripheral retinal photocoagulation to reduce the risk of retinal detachment.

Basilius et al. (2015) performed spectral domain-optical coherence tomography (SD-OCT) and FA in 5 female patients with IP who were under the age of 5 years. Two children had reduced visual behavior in association with abnormalities of the inner foveal layers on SD-OCT. FA showed filling defects in retinal and choroidal circulations and irregularities of the foveal avascular zones. The foveal to parafoveal ratios were greater than 0.57 in 6 eyes of 3 patients who had extraretinal neovascularization and/or peripheral avascular retina on FA and were treated with laser; of these, 3 eyes from 2 patients had irregularities in foveal avascular zones and poor vision. Basilius et al. (2015) concluded that vigilant surveillance in the early years of life may preserve vision in some patients with IP.

Mariath et al. (2018) reported 4 families, with a total of 15 cases of incontinentia pigmenti, all with the recurrent IKBKG deletion (300248.0001), with substantial intrafamilial clinical variability. Within each family, there were both mild and severe cases as well as varying types of involvement (skin, teeth, hair, eye, nail, and neurologic). The authors specifically analyzed the degree of dental involvement, ranging from tooth agenesis to abnormalities of dental crowns and high-arched palate, and noted that these findings also varied substantially within families. Given that all family members had the same IKBKG deletion, Mariath et al. (2018) proposed that other as yet unidentified modifying genes might influence disease expressivity.

Diagnosis

Based on a metaanalysis of clinical findings of IP reported in the literature, Minic et al. (2014) presented updated diagnostic criteria for the disorder. Major criteria included any of the 4 stages of skin lesions elucidated by Landy and Donnai (1993), and minor criteria included dental, ocular, central nervous system, hair, nail, palate, breast, and nipple anomalies, as well as multiple male miscarriages and histopathologic skin findings.

Prenatal Diagnosis

Devriendt et al. (1998) reported a family in which prenatal diagnosis of incontinentia pigmenti was performed by chorionic villus sampling at 10 weeks of gestation. Karyotype was 46,XY and DNA analysis showed that the fetus had inherited the haplotype carrying the familial IP allele. However, fetal findings on ultrasound were normal. Given the lack of data on the time of fetal death in males with IP, and since maternal mosaicism could not be excluded with certainty, it was decided to observe the spontaneous evolution of the pregnancy. Ultrasound examination at 20 weeks showed fetal death. Fetal movements had stopped 2 weeks before. Severe growth retardation was present. Fetopathologic examination showed pronounced maceration and no anomalies other than growth retardation.

Pathogenesis

The evolution of lesions can be interpreted as representing death of cells that have the mutant-bearing X chromosome as the active one and replacement of same by cells with the normal X active. The progression is from an erythematous eruption with linear vesiculation in the newborn period (the vesicobullous stage), followed by a verrucous stage. After a few months the verrucous growth drops off and leaves hyperpigmented areas. The third stage persists for several years and usually disappears at about age 20 years. This sequence would be expected to be accompanied by a marked reduction in cells with the mutant X active. Wieacker et al. (1985) tested this prediction. Fibroblasts from normal and hyperpigmented areas were fused with HPRT-deficient mouse RAG cells. From normal skin they isolated 13 hybrid clones and from hyperpigmented skin, 16 hybrid clones. Restriction patterns were consistent with the non-IP X chromosome being the active one in all clones. By way of contrast, in the Aicardi syndrome (304050), X inactivation was apparently at random. A problem in these cases is why there is a mosaic phenotype when the normal X is inactivated in most cells. Why is this not lethal as in the hemizygous male?

In a study of 5 females heterozygous for incontinentia pigmenti, Migeon et al. (1989) found that cells expressing the mutation were eliminated from skin fibroblast cultures and, to varying degrees, from hematopoietic tissues. The authors suggested that selection against cells carrying the mutant X may protect heterozygous females from the lethal effect of the mutation in the hemizygous state.

Munne et al. (1996) described the case of a 28-year-old woman with mild manifestations of IP2 and her daughter who showed classic features. The authors decided to use preimplantation genetic diagnosis based on the sexes of the embryos as determined by fluorescence in situ hybridization (FISH). They transferred only male embryos, on the assumption that any carriers among them would not survive. They tested for aneuploidy with FISH probes for chromosomes X, Y, 18, and 13/21. Unexpectedly, 57% of the embryos were found to be aneuploid for chromosomes 18, 13, or 21. The patient achieved pregnancy but spontaneously aborted a trisomy 9 fetus. Munne et al. (1996) commented that, to their knowledge, IP2 had not previously been linked to unusually high rates of aneuploidy.

Inheritance

Carney (1976) found 653 cases in the literature (593 females, 16 males, and 44 of unspecified sex). Pfeiffer (1960) proposed female-limited autosomal dominant inheritance. Lenz (1961) suggested X-linked dominant inheritance with lethality in the male. IP in a male with XXY Klinefelter syndrome (Kunze et al., 1977) is consistent with this hypothesis. Ormerod et al. (1987) described incontinentia pigmenti in a boy with XXY Klinefelter syndrome. Pedigree patterns suggested X-linked dominance with lethality in the male. The phenotype in the affected females might be consistent with random X chromosome inactivation as in the Lyon hypothesis. Cytoplasmic (or other nonchromosomal) inheritance with lethality in the male could also account for the pedigree pattern. Features of the histologic and clinical picture have suggested viral etiology to several workers (e.g., Haber, 1952). Cytoplasmic inclusions similar to those of molluscum contagiosum have been identified (Murrell, 1962). No chromosomal abnormality was found in 2 cases of incontinentia pigmenti studied by Benirschke (1962). In the family studied, the mother and 2 daughters were affected; there had been 1 male abortion.

Gartler and Francke (1975) suggested that half-chromatid mutations occurring during gametogenesis is a possible mechanism for mosaicism and a possible explanation for the occurrence of fewer than the theoretically expected one-third of cases of X-linked lethal disorders as new mutations. Lenz (1975) suggested that some male cases of incontinentia pigmenti may be mosaics originating in this way. He stated that 355 cases have been reported in females and 6 in males. The pattern of the skin changes is like that of the heterozygous state of some X-linked genes in animals. Mosaicism would account for a similar finding in XY males. Traupe and Vehring (1994) suggested that a more plausible explanation for mosaic skin lesions following the lines of Blaschko in boys with incontinentia pigmenti would be an unstable premutation that normally remains silent in males during early embryogenesis. Occasionally 'silencing' might be incomplete and give rise to clinically manifest IP reflecting a mosaic state of alleles with the full and the premutation in the same patient. Traupe and Vehring (1994) suggested that this model would account for mother-to-son transmission of IP as in the cases of Kurczynski et al. (1982) and Hecht et al. (1982) and for disparate phenotypes in monozygotic female twins. Traupe and Vehring (1994) pictured a 4-month-old boy with mosaic cutaneous involvement of IP predominantly on the right side; he had subtotal retinal detachment of the right eye and right abducens paralysis, as well as central motor dysfunction predominantly affecting the right arm and leg. An unstable premutation that became partially expressed during early embryogenesis was proposed as the explanation.

Garcia-Dorado et al. (1990) reported an XXY male with typical incontinentia pigmenti. The mother and maternal grandmother as well as a maternal aunt and her daughter had incontinentia pigmenti.

Kirchman et al. (1995) described a family in which 2 paternally related half sisters had incontinentia pigmenti. The father was healthy and clinically normal and had a 46,XY normal male karyotype. Linkage analysis of 12 polymorphic markers (2 X-linked and 10 autosomal) confirmed paternity. X inactivation studies with the human androgen receptor (313700) indicated that the paternal X chromosome was inactivated preferentially in each girl, implying that this chromosome carried the IP mutation and that the father was a gonadal mosaic for the IP mutation.

Mapping

Cases of X/autosome translocation suggested the existence of a form of incontinentia pigmenti due to chromosomal aberration in the vicinity of the centromere (IP1), whereas linkage studies with RFLPs suggested that IP is located in the Xq28 band (IP2). For discussion of IP1, see 300337.

Pallotta and Dalpra (1988) found no increased chromatid and chromosome gaps and breaks in 4 patients with incontinentia pigmenti. Sefiani et al. (1988) studied linkage in 5 IP families containing 29 potentially informative meioses. Using 10 probes of the Xp arm (including 6 that were precisely localized by somatic cell hybridization using a broken X chromosome derived from an IP patient carrying an X;9 translocation), Sefiani et al. (1988) found negative lod scores, which excluded linkage of the IP gene to Xp11. A major part of Xp was also excluded. Sefiani et al. (1989) studied 8 families in which 2 or more females were affected with IP. Using DNA markers, they excluded Xp11 and most of Xq as the site of the IP gene. They concluded that IP is linked to DXS52, which is located in Xq28 (maximum lod = 3.5 at theta = 0.05). Harris et al. (1988) used RFLPs mapping between Xp21 and Xq22.3 in linkage studies of IP. Although 6 independent sporadic cases with findings suggesting IP had been found to have X/autosome translocations involving an Xp11 breakpoint, Harris et al. (1988) could not confirm this localization in familial cases with RFLP markers.

Sefiani et al. (1991) corroborated the linkage of IP2 to DXS52; maximum lod score = 6.19 at recombination fraction = 0.03. Smahi et al. (1994) confirmed linkage between IP2 and F8C (300841); maximum lod = 11.85 at theta = 0.028. Linkage was established with distal markers, and multipoint analysis suggested that IP2 is distal to F8C in Xq28.

Jouet et al. (1997) performed linkage analysis in 16 families with multigenerational cases of incontinentia pigmenti. A high lod score was found for markers spanning the interval from DXS52 to DXYS154.

IP2 was shown to be caused by mutations in the NEMO gene (300248), which maps to Xq28, by The International Incontinentia Pigmenti Consortium (2000).

Molecular Genetics

For more complete discussion of the molecular genetics of this disorder, see the entry for the NEMO gene (300248).

The International Incontinentia Pigmenti Consortium (2000) demonstrated that mutations in NEMO cause incontinentia pigmenti type II. The most common mutation in IP2 is a genomic rearrangement resulting in deletion of part of the NEMO gene (300248.0001). It was stated that this rearrangement, which occurs during paternal meiosis, causes 80% of new mutations. The origin of mutation was established for 12 patients with the rearrangement. Ten of the mutations occurred during male gametogenesis, implicating intrachromosomal interchange. In 9 of 47 IP patients found not to have the rearrangement, 6 were screened for intragenic changes and 4 were found to have mutations. These segregated with the disease in families or arose de novo with the disease, indicating that defects in NEMO alone are sufficient to cause the disorder. NEMO is essential for NF-kappa-B (see 164011) activation. Embryonic fibroblasts from IP patients demonstrated lack of NF-kappa-B activation upon electrophoretic mobility shift assay. Since activated NF-kappa-B normally protects against TNF-alpha-induced apoptosis, IP cells are highly sensitive to proapoptotic signals.

The International Incontinentia Pigmenti Consortium (2000) reported 1 liveborn male with a mutation in NEMO. He was the affected son of a classically affected IP female. He was born with multiple capillary hemangiomas, developed lymphedema of the lower limbs, and failed to thrive owing to malabsorption. Despite a destructive red blood cell picture and recurrent infections due to poor immune cell function, he survived 2 and a half years, then succumbed to tuberculosis infection. He had had operations to remove his spleen and a gut stricture, and biopsies revealed abnormal capillary beds in the gut, extrahepatic erythropoiesis, and osteopetrosis. His skin developed a reticular pigmentation. Cognitive development was normal. This patient had a mutation in the stop codon resulting in NEMO protein with 27 extra amino acids (300248.0002). Mansour et al. (2001) further described this patient and hypothesized that this mutation was likely to have a less severe effect on NEMO activity, possibly accounting for his survival until age 2 years and 7 months.

By mutation screening, Aradhya et al. (2000) excluded 4 candidate genes that map to Xq28: filamin (300017), plexin (300022), palmitoylated membrane protein-1 (305360), and von Hippel-Lindau binding protein (300133).

The DKC1 gene (300126) maps to the same region as IP, and mutations in this gene cause the dyskeratosis congenita phenotype (305000), which has similarities to IP. Heiss et al. (1999) studied 23 females and 1 aborted male fetus with IP by SSCP, 2 aborted male fetuses by PCR and sequencing, and 50 females and 4 males by Southern blot analysis using DKC1 cDNA as probe. No mutations were detected. Heiss et al. (1999) concluded that IP and dyskeratosis congenita are not allelic, but cautioned that their analysis would not have detected mutations in the promoter or untranslated regions.

In an examination of families transmitting the recurrent deletion of exons 4 through 10 of the NEMO gene (300248.0001), Aradhya et al. (2001) revealed that the rearrangement occurred in the paternal germline in 70% of cases, indicating that it arises predominantly by intrachromosomal misalignment during meiosis. Expression analysis of human and mouse NEMO/Nemo showed that the gene becomes active early during embryogenesis and is expressed ubiquitously. The authors proposed a model to explain the pathophysiology of IP in terms of disruption of the NF-kappa-B signaling pathway.

Nomenclature

Sybert (1994) suggested that the IP1/IP2 nomenclature is 'premature and misleading' and argued for 'the quick and early consignment of the terms...to the anomalad graveyard.' She contended that what has been called IP2 is the classic disorder described by Bloch (1926) and Sulzberger (1927), i.e., the male-lethal, X-linked dominant disorder due to a gene located in the Xq28 region. On the other hand, 'IP1' is not incontinentia pigmenti at all. She tabulated 40 cases of X/autosome translocations with a phenotype designated as 'incontinentia pigmenti' and argued that none of them satisfied the diagnostic criteria. She suggested the alternative descriptive phrase 'X-autosome translocation associated with pigmentary abnormality.'

A historical example of a similar nomenclature mistake was the use of the term 'incontinentia pigmenti achromians' interchangeably with the term 'hypomelanosis of Ito.' It suggested an unwarranted association of hypomelanosis of Ito with classic incontinentia pigmenti. Hypomelanosis of Ito is a phenotype well recognized to be associated with chromosomal mosaicism in many cases. None of the patients have peg-shaped teeth or typical retinal vascular changes of incontinentia pigmenti.

Happle (1998) concluded that there is convincing evidence that the 'sporadic type of incontinentia pigmenti' (IP1) does not exist. He stated that the delineation of IP1 represented a historical misunderstanding. A locus proposed for this disorder was Xp11 (Gilgenkrantz et al., 1985; Kajii et al., 1985; Hodgson et al., 1985; Gorski et al., 1991). Because all cases of so-called incontinentia pigmenti showing an association with this locus were sporadic, the name 'sporadic type of incontinentia pigmenti' was given to the phenotype to distinguish it from familial incontinentia pigmenti. Happle (1987) suggested that investigators reporting an association between incontinentia pigmenti and Xp11 had, in fact, not mapped incontinentia pigmenti, but rather hypomelanosis of Ito. Inflammation or blistering of the skin was absent, which would be unusual in incontinentia pigmenti. Thereafter it became clear that hypomelanosis of Ito may not be a discrete entity but a skin disorder that is merely a symptom of many different states of mosaicism. Besides various autosomal regions, Xp11 is rather frequently involved in phenotypes that should be categorized as hypomelanosis of Ito. In cases of pigmentary mosaicism involving Xp11, the skin lesions are never preceded by an inflammatory stage as observed in incontinentia pigmenti. In those cases of hypomelanosis of Ito where no mosaicism can be demonstrated by cytogenetic examination, it is possible that either mosaicism is present at the molecular level or that a minor cytogenetic aberration had gone unnoticed. Jewett et al. (1997) reevaluated a case of de novo unbalanced X;autosome translocation reported by Pettenati et al. (1993) and concluded that it was the case representing confirmation of the association with incontinentia pigmenti with Xp11. Happle (1998) pointed out that the patient lacked typical neonatal inflammatory signs of incontinentia pigmenti and was more likely to represent hypomelanosis of Ito.

Animal Model

Eldridge and Atkeson (1953) suggested that the 'striated' mutation in mice and 'streaked hairlessness' in cattle are homologous to either focal dermal hypoplasia (FDH; 305600) or incontinentia pigmenti in man. In the second of the animal disorders, approximately perpendicular, irregularly narrow streaks of hide on various parts of the cow are affected. No males are affected. A deficiency of sons and an increased length of calving-interval in affected females support X-linked dominant inheritance with lethality in the male at an early embryonic stage.

'Striated' (Str) is a semidominant X-linked mutation of the mouse that had been regarded as possibly the murine equivalent of IP2 (Phillips, 1963). Hemizygous males die at about 11 to 13 days of gestation (Green, 1989). Liu et al. (1999) showed that striated and bare patches (Bpa) mice have mutations in the Nsdhl gene (300275). Aradhya et al. (2000) searched for mutations in the NSDHL gene in 24 patients with incontinentia pigmenti; no mutations were identified.

By gene targeting, Rudolph et al. (2000) generated mice deficient in Nemo, mutations in which cause IP2 in humans (The International Incontinentia Pigmenti Consortium, 2000). Mutant embryos died at embryonic day 12.5-13 from severe liver damage due to apoptosis. The International Incontinentia Pigmenti Consortium (2000) stated that for Nemo-deficient heterozygous female mice, a phenotype comparable to that seen in man had not been reported. They further noted that owing to lyonization, understanding the effects observed in human patients was difficult.