Incontinentia pigmenti achromians (hypomelanosis of ITO, MIM 146150): further evidence of localization at Xp11

Pigmentary mosaicism: a review of original literature and recommendations for future handling

Background

Pigmentary mosaicism is a term that describes varied patterns of pigmentation in the skin caused by genetic heterogeneity of the skin cells. In a substantial number of cases, pigmentary mosaicism is observed alongside extracutaneous abnormalities typically involving the central nervous system and the musculoskeletal system. We have compiled information on previous cases of pigmentary mosaicism aiming to optimize the handling of patients with this condition. Our study is based on a database search in PubMed containing papers written in English, published between January 1985 and April 2017. The search yielded 174 relevant and original articles, detailing a total number of 651 patients.

Results

Forty-three percent of the patients exhibited hyperpigmentation, 50% exhibited hypopigmentation, and 7% exhibited a combination of hyperpigmentation and hypopigmentation. Fifty-six percent exhibited extracutaneous manifestations. The presence of extracutaneous manifestations in each subgroup varied: 32% in patients with hyperpigmentation, 73% in patients with hypopigmentation, and 83% in patients with combined hyperpigmentation and hypopigmentation. Cytogenetic analyses were performed in 40% of the patients: peripheral blood lymphocytes were analysed in 48%, skin fibroblasts in 5%, and both analyses were performed in 40%. In the remaining 7% the analysed cell type was not specified. Forty-two percent of the tested patients exhibited an abnormal karyotype; 84% of those presented a mosaic state and 16% presented a non-mosaic structural or numerical abnormality. In patients with extracutaneous manifestations, 43% of the cytogenetically tested patients exhibited an abnormal karyotype. In patients without extracutaneous manifestations, 32% of the cytogenetically tested patients exhibited an abnormal karyotype.

Conclusion

We recommend a uniform parlance when describing the clinical picture of pigmentary mosaicism. Based on the results found in this review, we recommend that patients with pigmentary mosaicism undergo physical examination, highlighting with Wood’s light, and karyotyping from peripheral blood lymphocytes and skin fibroblasts. It is important that both patients with and without extracutaneous manifestations are tested cytogenetically, as the frequency of abnormal karyotype in the two groups seems comparable. According to the results only a minor part of patients, especially those without extracutaneous manifestations, are tested today reflecting a need for change in clinical practice.

Electronic supplementary material

The online version of this article (10.1186/s13023-018-0778-6) contains supplementary material, which is available to authorized users.

Pigmentary disorders of the eyes and skin

Oculocutaneous albinism, Menkes syndrome, tuberous sclerosis, neurofibromatosis type 1, dyskeratosis congenita, lentiginosis profusa syndrome, incontinentia pigmenti, and Waardenburg syndrome all are genodermatoses that have well established gene mutations affecting multiple biological pathways, including melanin synthesis, copper transport, cellular proliferation, telomerase function, apoptosis, and melanocyte biology. Onchocerciasis results from a systemic inflammatory response to a nematode infection. Hypomelanosis of Ito is caused by chromosomal mosaicism, which underlies its phenotypic heterogeneity. Incomplete migration of melanocytes to the epidermis and other organs is the underlying feature of nevus of Ota. Vogt-Koyangi-Harada and vitiligo have an autoimmune etiology; the former is associated with considerable multiorgan involvement, while the latter is predominantly skin-limited.

Patterned pigmentation in children

The terms pigmentary mosaicism or patterned dyspigmentation describe a spectrum of clinical findings that range from localized areas of dyspigmentation with no systemic findings to widespread dyspigmentation with associated neurologic, musculoskeletal, and cardiac abnormalities, and other sequelae that can lead to early demise. Given this wide spectrum, these patients must be approached with caution, but with the understanding that most who have localized pigmentary anomalies, such as segmental pigmentary disorder (SegPD) seem to have no systemic manifestations. These patients can be approached in many different ways, but generally children with more widespread dyspigmentation, and any with associated abnormalities or not meeting neurodevelopmental milestones, should be evaluated closely. Children with any red flags warrant subspecialty referral, and all children deserve close clinical follow-up with their primary care physician to ensure they meet all of their developmental milestones. Fortunately, parents can be reassured that most children with SegPD, and many with more widespread patterned pigmentation, are otherwise healthy.

Heterogeneous seizure manifestations in Hypomelanosis of Ito: report of four new cases and review of the literature

Hypomelanosis of Ito (HI) is a rare neuroectodermal disorder often associated with mental retardation and epilepsy. We report on four new HI patients presenting with heterogeneous seizure manifestations and we review the literature concerning epileptic seizures in HI. At one extreme, there are patients with generalized seizures well controlled by drug treatment, whereas at the opposite there are patients with severe, often pharmacoresistant, focal seizures. The genetic substrate for HI syndrome is not homogenous and only partially understood. Further researches are required to shed light on the pathogenesis of HI phenotypes.

Familial whole-arm translocations (1;19), (9;13), and (12;21): a review of 101 constitutional exchanges

We report here on 3 familial whole-arm translocations (WATs), namely the 8th instance of t(1;19)(p10;q10) and 2 novel exchanges: t(9;13)(p10;q10) and t(12;21)(p10;q10). The exchanges (1;19) and (12;21) were ascertained through a balanced carrier, whereas the t(9;13) was first diagnosed in a boy with a trisomy 9p syndrome and der(9p13p). Results of FISH analyses with the appropriate ?-satellite probes were as follows. Family 1, t(1;19): the D1Z5 probe gave a strong signal on both the normal chromosome 1 and the der(1q19p) as well as a weak signal on the der(1p19q). Family 2, t(9;13): the centromere-9 alphoid and D13Z1/D21Z1 probes under standard stringency gave no signal on the der(9p13p) in both the proband and a carrier brother, whereas the der(9q13q) was labelled only with the centromere-9 alphoid repeat in the latter; yet, this probe under low stringency revealed a residual amount of alphoid DNA on the der(9p13p) in the carrier. Family 3, t(12;21): the D12Z3 probe gave a signal on the normal chromosome 12 and the der(12p21q), whereas the D13Z1/D21Z1 repeat labelled the der(12q21p), the normal chromosome 21, and both chromosomes 13. Out of 101 WATs compiled here, 73 are distinct exchanges, including 32 instances between chromosomes with common alphoid repeats. Moreover, 7/9 of recurrent WATs involved chromosomes from the same alphoid family. Thus constitutional WATs appear to recur more frequently than other reciprocal exchanges, often involve chromosomes with common alphoid repeats, and can mostly be accounted for the great homology in alphoid DNA that favours mispairing and illegitimate nonhomologous recombination.

Abnormal pigmentation in hypomelanosis of Ito and pigmentary mosaicism: the role of pigmentary genes

There is increasing evidence that hypomelanosis of Ito and related disorders such as linear and whorled naevoid hypermelanosis are due to mosaicism for a variety of chromosomal abnormalities. This group of disorders is better termed 'pigmentary mosaicism'. In this review we explain how disparate chromosomal abnormalities might manifest as a common pigmentary phenotype. In particular, we provide evidence supporting the hypothesis that the chromosomal abnormalities reported in these disorders specifically disrupt expression or function of pigmentary genes.

Pigmentary mosaicism of the hyperpigmented type in two half-brothers

Pigmentary mosaicism is a heterogeneous cutaneous phenotype that is often associated with extracutaneous anomalies. It is widely accepted that these phenotypes arise de novo as a result of a postzygotic mutation, leading to a mosaic status of the embryo. In the vast majority of cases, the occurrence of pigmentary mosaicism is sporadic. We report two paternal half-brothers affected with pigmentary mosaicism of the hyperpigmented type. The hyperpigmentation in both patients is distributed along the lines of Blaschko. In addition, mental retardation, facial asymmetry, short stature, scoliosis, and short fingers with clinodactyly of the 5th digit were noted in one of them. Chromosome analysis in this 15-year-old patient demonstrated a mosaic 46,XY,dup(3)(p21.3;pter)/46,XY with 12% aberrant cells in lymphocytes and 2% in skin fibroblasts derived from a hyperpigmented area. His nine-year-old half-brother had similar systematized hyperpigmented skin lesions, macrocephaly, facial asymmetry, and clinodactyly of the 5th digit. Chromosome analysis of peripheral lymphocytes showed a normal karyotype 46,XY. A skin biopsy could not be obtained. So far, some familial cases of hypopigmentation along the lines of Blaschko have been reported, but familial occurrence of the hyperpigmented type of pigmentary mosaicism appears to be extremely unusual. It is difficult to establish a causal relationship with the chromosomal mosaicism as observed in patient 1. Paradominant transmission seems unlikely because this would likewise imply that the chromosomal mosaicism is an incidental finding.

Hypomelanosis of ito and a 'mirror image' whole chromosome duplication resulting in trisomy 14 mosaicism

We describe a female infant with multiple congenital anomalies including unusual hyperpigmentation, tetralogy of Fallot, absent corpus callosum and wide prominent nasal bridge. The infant was initially seen for genetic consultation on day one after birth. Chromosome analysis from cultured lymphocytes showed a normal 46,XX karyotype. However, cultured skin fibroblasts showed mosaicism with 46,XX,add(14)(q32).ish psu dic dup(14)(q32p13)(wcp14+)/46,XX complements. A review of the published report with chromosome mosaicism and hypomelanosis of Ito (HMI) is included. We suggest that the trisomy 14 mosaicism seen in fibroblast cultures has importance in the expression of pigmentation dysplasias in this patient. Pigmentary anomaly may be due to loss or gain of specific genes that influence pigmentation located on the long arm of chromosome 14 in this patient.

Functional Xp disomy and hypomelanosis of Ito

BACKGROUND

Hypomelanosis of Ito (HI) is a neurocutaneous phenotype that reflects different mosaicisms, including functional imbalances secondary to chromosome-X inactivation patterns in certain X;autosome translocation carriers.

METHODS

We assessed X inactivation patterns by means of the human androgen receptor (HUMARA) assay and BrdU labeling in affected and unaffected skin of a young female with HI and a de novo t(X;13)(Xp13q;Xq13p). PCR analysis was carried out in DNA extracted from uncultured and cultured skin, whereas the BrdU replication patterns were sought in cultured fibroblasts. Parental DNA was also tested. Fluorescence in situ hybridization (FISH) with X and 13/21 centromere probes (DXZ2 and D13Z1/D21Z1) and a cosmid for the X inactivation center were also performed to refine breakpoint assignments.

RESULTS

An X inactivation pattern implying functional Xpter-->q11 disomy was found in DNA extracted from uncultured hypopigmented skin, whereas preferential inactivation of the normal X was observed in uncultured normal skin as well as in cultured fibroblasts (after one passage) from both affected and unaffected skin areas. PCR analysis also showed paternal origin of the translocation. BrdU labeling of metaphases from hypopigmented and normal skin primary cultures showed der(Xq13p) to be inactive in about 25% of the cells. FISH revealed that der(Xp13q) had a compound centromere, whereas der(Xq13p) retained 13 centromere repeats but lacked X centromere sequences. Hence, breakpoints were assigned to Xq11 and 13q10. The X inactivation center cosmid gave a signal on both normal X and der(Xp13q), indicating that the inactivation center was not disrupted by the translocation.

CONCLUSIONS

These findings confirm that mosaic functional Xp disomy, rather than disruption of X-linked genes, is associated with HI and involvement of the central nervous system (CNS) in some carriers of a structurally balanced X;autosome translocation.

Hypomelanosis of ITO. A study of 76 infantile cases

We show the complications observed in a large series of children with hypomelanosis of Ito (HI) or incontinentia pigmenti achromians, studied in a neurology service over 30 years. Of the 76 patients, 35 were male (46%) and 41 female (54%) with ages ranging from newborn to 10 years at the time of the first visit. They were thoroughly studied from the clinical, genetic, psychological, neuroradiological, with computed tomography (CT) and/or magnetic resonance imaging (MRI), and electroencephalographic (EEG) points of view. Mental retardation was observed in 43 cases (57%) of whom eight (10%) showed autistic behavior; 16 (21%) were borderline and only 17 (22%) had a normal mental level (IQ > 85). Thirty-seven patients (49%) had seizures, consisting of infantile spasms in six cases (8%). Twelve cases showed macrocephaly and coarse facies, six had microcephaly, and 14 showed hypotonia with pes valgus and genu valgus. Three cases of cerebellar hypoplasia, another of intracranial arteriovenous malformation and another of distal spinal muscular atrophy were observed as well. Some other anomalies, such as syndactyly, clinodactyly, abnormalities of the skeleton, asymmetry of the facies, ears, body and/or extremities, gynecomastia and asymmetrical breasts, short stature, oral alterations, congenital cardiopathies and genital anomalies, were also occasionally found. Three children died, but necropsy was performed only in one. Anatomical and histological studies did not disclose specific findings.

Hypomelanosis of Ito: a syndrome requiring a multisystem approach

Hypomelanosis of Ito can be defined as a syndrome providing a cutaneous epiphenomenon with a peculiar pattern of distribution, usually associated with disorders of the nervous system, skeleton and eyes. Four further patients are reported and the literature reviewed. The diagnostic criteria and the differences with other pigmentary diseases distributed along Blaschko's lines are highlighted. The main histopathological features are reported and the high frequency of the associated abnormalities are emphasized. The chromosomal findings and main genetic hypotheses are discussed. The suggested follow-up aims not only at the knowledge of the natural history of this condition, but also at its better delineation.

Linear hypopigmentation and hyperpigmentation, including mosaicism

Linear streaks of hypopigmentation or hyperpigmentation along Blaschko's lines are currently grouped under the names hypomelanosis of Ito (HI) and linear and whorled hypermelanosis (LWH). Recent studies have suggested that these linear pigmentary anomalies reflect underlying genetic mosaicism. Mosaic individuals are composed of two or more genetically distinct cell populations, a normal and an abnormal population. In HI and LWH, the types of genetic defects that are detectable in the abnormal population are highly variable, including tetraploidy, partial or complete trisomies, translocations, and point mutations. These results, together with recent studies indicating the incidence of extracutaneous anomalies is lower in HI but higher in LWH than previously estimated, have important clinical implications. The need for a revised nomenclature as well as possible modifications in current recommendations for patient management are discussed.

Functional Xp disomy and de novo t(X;13)(q10;q10) in a girl with hypomelanosis of Ito

We report on a 16 month old girl with hypomelanosis of Ito and a balanced de novo (X;13)(q10;q10) translocation in which the der(Xp13q) had the X centromere (as assessed by FISH with the DXZ3 probe). A functional Xp disomy was shown in a small proportion of cultured lymphocytes by means of a BrdU terminal pulse. This observation supports the notion of a distinct form of hypomelanosis of Ito resulting from a functional Xp disomy.

Hypomelanosis of Ito and brain abnormalities: MRI findings and literature review

We report the results of a 14-year retrospective study of brain MRI abnormalities in 12 pediatric patients presenting with hypomelanosis of Ito (HI). Miscellaneous brain abnormalities were found: one patient had a medulloblastoma, three had cortical malformations, and five demonstrated "minor" abnormalities such as dilated Virchow-Robin spaces or brain atrophy. We emphasize the polymorphism of brain abnormalities associated with HI.

X inactivation analysis in a female with hypomelanosis of Ito associated with a balanced X;17 translocation: evidence for functional disomy of Xp

X inactivation analysis was performed on normal and hypopigmented skin samples obtained from a female with hypomelanosis of Ito associated with a balanced whole arm X;17 translocation. Severe skewing of X inactivation resulting in inactivity of the intact X was found in blood and cultures of both types of skin, but analysis of DNA prepared directly from hypopigmented skin showed significant inactivation of the translocated X, inconsistent with the usual mechanism of phenotypic expression in X;autosome translocations. In addition, dual colour FISH analysis using centromere specific probes for chromosomes X and 17 showed that the breakpoints on both chromosomes lie within the alphoid arrays, making interruption of a locus on either chromosome unlikely. While partial variable monosomy of loci on chromosome 17p cannot be excluded as contributing to the phenotype in this patient, it is argued that the major likely factor is partial functional disomy of sequences on Xp in cell lineages that have failed to inactivate the intact X chromosome.

Hypomelanosis of Ito and X;autosome translocations: a unifying hypothesis

Hypomelanosis of Ito is a sporadic multisystem disorder known to be associated in many cases with chromosomal mosaicism. While no particular pattern is generally evident for the specific chromosomes involved in such patients, a subgroup of female patients exists in whom the common factor is the presence of a balanced, constitutional X;autosome translocation, with a cytogenetic breakpoint in the pericentromeric region of the X. It is argued here that the phenotype in these cases results not from the interruption of X linked genes but from the presence of mosaic functional disomy of X sequences above the breakpoint.

Ectodermal dysplasias: a clinical classification and a causal review

We present a casual review of 154 ectodermal dysplasias (EDs) as classified into 11 clinical subgroups. The number of EDs in each subgroup varies from one to 43. The numbers of conditions due to autosomal dominant, autosomal recessive, and X-linked genes are, respectively, 41, 52, and 8. In 53 conditions cause is unknown; 35 of them present some causal (genetic) suggestion.