Cytogenetic and dermatoglyphic findings in a familial case of hypomelanosis of Ito (incontinentia pigmenti achromians)

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.

Tetraploid-diploid mosaicism in a patient with pigmentary anomalies of hair and skin: a new dermatologic feature

Tetraploid-diploid mosaicism in humans is exceedingly rare. We present an 11-year-old boy with tetraploid-diploid mosaicism and coexistent hair hypopigmentation with skin hypo- and hyperpigmentation. This case expands the current literature as we are not aware of previous documentation of this unique combination of pigmentary anomalies.

Hypomelanosis of Ito

Hypomelanosis of Ito, initially referred to as incontinentia pigmenti achromians, is a rare neurocutaneous disorder. Hypopigmented lesions following the lines of Blaschko are usually the presenting feature. Multiple organ systems can be involved including brain, musculoskeletal, cardiovascular, eyes, kidneys, and teeth. The neurologic complications can include seizures, hemimegalencephaly, developmental delay and abnormalities in tone. Genetic mosaicism is the most likely explanation for its inheritance. It must be distinguished from incontinentia pigmenti because at early stages, skin lesions can appear similar between the two conditions. Consensus recommendations for screening of associated extracutaneous conditions do not exist and management is symptomatic, but regular evaluation of somatic growth, neurodevelopment, endocrine status, eyes, and teeth should occur. Initial screening of renal function has also been recommended. Awareness of this disorder will allow for diagnosis, genetic counseling and appropriate screening.

Hypomelanosis of Ito with a trisomy 2 mosaicism: a case report

INTRODUCTION

Hypomelanosis of Ito is a rare neurocutaneous disorder, characterized by streaks and swirls of hypopigmentation following the lines of Blaschko that may be associated to systemic abnormalities involving the central nervous system and musculoskeletal system. Despite the preponderance of reported sporadic hypomelanosis of Ito, few reports of familial hypomelanosis of Ito have been described.

CASE PRESENTATION

A 6-month-old Caucasian girl presented with unilateral areas of hypomelanosis distributed on the left half of her body and her father presented with similar mosaic hypopigmented lesions on his upper chest. Whereas both blood karyotypes obtained from peripheral lymphocyte cultures were normal, a 16% trisomy 2 mosaicism was found in cultured skinfibroblasts derived from a hypopigmented skin area of her father.

CONCLUSIONS

Familial cases of hypomelanosis of Ito are very rare and can occur in patients without systemic involvement. Hypomelanosis of Ito constitutes a non-specific diagnostic definition including different clinical entities with a wide phenotypic variability, either sporadic or familial. Unfortunately, a large number of cases remain misdiagnosed due to both diagnostic challenges and controversial issues on cutaneous biopsies in the pediatric population.

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.

Diploid/tetraploid/t(1;6) mosaicism in a 17-year-old female with hypomelanosis of Ito, multiple congenital anomalies, and body asymmetry

Many types of chromosome mosaicism have been identified in cases of hypomelanosis of Ito, often in association with chromosome instability; however, there have been very few cases with diploid-tetraploid mosaicism described in the literature. We present a patient with a tetraploid mosaicism: a 17-year-old girl who has hypomelanosis of Ito in association with diploid/tetraploid/t(1;6) mosaicism. She had multiple congenital anomalies of omphalocele, exstrophy of bladder, duodenal web, and imperforate anus. These features have not been described previously in diploid-tetraploid mosaicism.

Prenatally detected trisomy 7 mosaicism in a dysmorphic child

Trisomy 7 mosaicism was detected prenatally in cultured amniocytes but not in fetal lymphocytes. The child that was born had pigmentary changes of the skin and facial asymmetry suggestive of a chromosomal mosaicism. Skin fibroblasts were studied and trisomy 7 mosaicism was confirmed. At 3 years of age the boy had developed mentally within normal limits. However, dysmorphic findings include sparse hair, short left palpebral fissure, ptosis of the left eyelid, strabismus, enamel dysplasia, low-set and posteriorly rotated ears and undescended testes. These findings share some common features with previously reported cases of trisomy 7 mosaicism.

Hypomelanosis of Ito: clinical syndrome or just phenotype?

The term hypomelanosis of Ito is applied to individuals with skin hypopigmentation along the lines of Blaschko. Even though originally described as a purely cutaneous disease, subsequent reports have included a 33% to 94% association with multiple extracutaneous manifestations mostly of the central nervous and musculoskeletal systems leading to frequent characterization as a neurocutaneous disorder. A number of reports claimed familial occurrence and supported single gene inheritance for hypomelanosis of Ito, but none has been proved. Miscellaneous chromosomal mosaicisms have been demonstrated in some but not all affected individuals. Thus, it has been suggested that hypomelanosis of Ito is not a single condition but rather a nonspecific manifestation (ie, a phenotype) of chromosomal mosaicism and that this term should now be dropped. In this article, we review these developments focusing on the neurologic and genetic aspects of hypomelanosis of Ito. Our personal experience with 41 hypomelanosis of Ito patients and literature review led us to conclude that (1) the term hypomelanosis of Ito has been often misapplied to individuals with nonspecific "patchy depigmentation of the skin" who had several conditions of different etiologies; (2) the white matter involvement seen at neuroimaging in most of our hypomelanosis of Ito patients was similar to that reported in well-defined neurocutaneous disorders, including Sjögren-Larsson syndrome and incontinentia pigmenti; (3) whatever figures we take for associated central nervous system abnormalities in hypomelanosis of Ito, these represent the most frequent extracutaneous findings and, therefore, the use of the term neurocutaneous disorder for hypomelanosis of Ito might well be appropriate.

Hypomelanosis of Ito: no entity, but a cutaneous sign of mosaicism

Hypomelanosis of Ito is a neurocutaneous phenotype comprising pigmentary anomalies, neurological defects, structural malformations, and chromosomal abnormalities. It has been described as a distinct multisystem birth defect or, more specifically, as a neurocutaneous syndrome. The main purpose of this study is to provide evidence that this disorder does not exist as a syndrome. Rather, it is a causally nonspecific pigmentary disorder caused by genetic mosaicism.

Neurocutaneous syndromes associated with pigmentary skin lesions

Tremendous strides have been made in our understanding of genetic disorders, including those that involve both the skin and the nervous system. The list of well-established neurocutaneous syndromes has increased during a few decades from a few classical phakomatoses to more than 30 entities. The dermatologist has the opportunity to facilitate precise diagnosis and optimal care for these patients by recognition of the cutaneous markers for these diseases. We have attempted to provide an overview of some recent advances in those syndromes manifested by pigmentary skin changes, emphasizing the clinical spectrum of each disorder and providing guidelines for an approach to management.

Selective decrease of eumelanin in hypopigmented epidermis of hypomelanosis of Ito

A Japanese infant had bilateral hypopigmented macules in a whorled or marble-cakelike configuration on her trunk and extremities. Her irides were bluish gray and her hair was dark brown. She had photophobia and macrocephaly with developmental delay. Analysis of peripheral lymphocytes and dermal fibroblasts disclosed a normal chromosomal pattern. A new finding was that the eumelanin content of the hypopigmented epidermis was decreased. We suggest that at least a portion of patients with this disorder have a defect in eumelanogenesis in hypopigmented skin.

Asymmetry and skin pigmentary anomalies in chromosome mosaicism

We report six persons mosaic for a chromosome anomaly. All were mentally retarded and dysmorphic. Unilateral or asymmetrical features were found in all cases, in one an unusual transverse terminal limb anomaly, and in the others various degrees of hemiatrophy of the left side of the body. Five of the subjects had skin pigmentary anomalies which were distributed in the lines of Blaschko. The abnormal cell lines found were ring chromosome 22, trisomy 22, a large acrocentric marker, a deletion of 18q, a deletion of 8q, and triploidy. In four cases the clinical diagnosis was only confirmed by skin biopsy. In one case low level mosaicism in blood was fortuitously detected because of cytogenetic fragile X screening and confirmed in a skin biopsy. The sixth case was of dynamic mosaicism of a non-mosaic deletion 18q with a chromosome 18 derived marker present in a proportion of cells. Chromosome mosaicisn may cause subtle and asymmetrical clinical features and can require repeated cytogenetic investigations. The diagnosis should be actively sought as it enables accurate genetic counselling to be given.

Lines of Blaschko

The lines of Blaschko represent a pattern followed by many skin disorders. We review the clinical and histologic features of X-linked, congenital/nevoid, and acquired skin diseases that follow these lines. We also include cutaneous disorders that have a linear distribution but do not follow Blaschko's lines. Finally, we differentiate Blaschko's lines from other patterns on the skin such as dermatomes and Langer's lines.