Mosaic Manifestation of Autosomal Dominant Skin Disorders

Abstract

A mosaic arrangement of skin lesions has been been noted in numerous autosomal dominant traits including hereditary multiple skin tumors, disorders of keratinization, diseases of the connective tissue or bones, and vascular disorders. Hereditary multiple skin tumors originate from allelc loss and thus represent mosaics. Multiple lesions may sometimes involve only a segmental area, in the form of type 1 mosaicism. Moreover, a pronounced segmental involvement may be superimposed on the ordinary, nonsegmental trait, in the form of type 2 mosaicsm. - Both type 1 and 2 manifestations have been documented in many autosomal dominant traits such as trichoepitheliomatosis, hereditary basaloid follicular hamartoma, multiple syringoma, multiple spiradenoma, glomangiomatosis, blue rubber bleb angiomatosis, neurofibromatosis 1, neurofibromatosis 2, leiomyomatosis, Gorlin syndrome, and hereditary non-syndromic basal cell carcinoma. – Examples of type 1 segmental involvement were reported in multiple trichodiscoma, cylindromatosis, schwannomatosis, and mastocytosis. – Cases suggesting a type 2 segmental manifestation were reported in Hornstein-Knickenberg syndrome (illegitimately named “Birt-Hogg-Dubé syndrome”), Legius syndrome, and PTEN hamartoma syndrome. Some hereditary tumor syndromes such as leiomyomatosis, neurofibromatosis 1, glomangiomatosis, and blue rubber bleb angiomatosis appear to be especially prone to develop a type 2 segmental involvement. Molecular proof of type 2 mosaicism has so far been provided in Gorlin syndrome, neurofibromatosis 1, Legius syndrome, and PTEN hamartoma syndrome. Disorders of keratinisation: Both type 1 and type 2 segmental involvement has been documented in patients with epidermolytic ichthyosis of Brocq, Darier disease, Hailey-Hailey disease, KID syndrome, disseminated superficial actinic porokeratosis, and plaque-type porokeratosis of Mibelli. Remarkably, a woman with porokeratosis of Mibelli gave birth to two sons who both had linear lesions in the form of a type 2 segmental involvement. Hence the underlying gene locus may be a hotspot for postzygotic recombination, as also assumed in disseminated superficial actinic porokeratosis. Molecular proof of type 1 mosaicism has so far been provided in epidermolytic ichthyosis of Brocq, Darier disease, and KID syndrome. Molecular evidence of type 2 mosaicism was presented in cases of Darier disease and Hailey-Hailey disease. – Cases of type 1 mosaicism with molecular proof were reported in pachyonychia congenita of the Jadassohn-Lewandowsky type and in the Galli-Galli variant of Dowling-Degos disease, and clinical examples without molecular data were reported in Costello syndrome and acrokeratoelastoidosis. – Moreover, cases suggesting type 2 mosaicism have been documented, without molecular data, in autosomal dominant acanthosis nigricans, autosomal dominant dyskeratosis congenita, and porokeratosis palmaris, plantaris et disseminata. Disorders of connective tissue or bones: Both type 1 and type 2 mosaicism has been documented in tuberous sclerosis and in autosomal dominant forms of Ehlers-Danlos syndromes. In tuberous sclerosis, molecular proof of type 1 segmental involvement was provided. Clinical features suggesting a type 2 segmental manifestation are frequently noted and described under various names such as cobblestone nevus, forehead patch, or fibrous hamartoma of infancy. – A type 1 segmental involvement in the form of pigmentary disturbances following Blaschko’s lines was documented in a girl with Brachmann-de Lange syndrome, a multisystem birth defect characterized by short stature, peculiar facial appearance, bone anomalies, and mental deficiency. – Cases suggesting a type 2 segmental involvement were reported, under the name “juvenile elastoma”, in patients with Buschke-Ollendorff syndrome. Remarkably, such pronounced segmental lesions are rather often noted in several members of a family, indicating that the underlying LEMD3 locus may be a hotspot for postzygotic recombination. Moreover, a particular bone disease called melorheostosis may occur as an extracutaneous type 2 manifestation of Buschke-Ollendorff syndrome. – Cases suggesting a type 2 segmental involvement have also been described in Marfan syndrome and Ehlers-Danlos syndrome type III. In Albright’s hereditary osteodystrophy, several persuasive examples of type 2 segmental involvement were found in the literature. – In hereditary osteomatosis cutis, cases of type 2 mosaic manifestation are so impressive that they have even got its own OMIM number 166350 under the name “progressive osseous heteroplasia”. – A girl with Zimmermann-Laband syndrome, a phenotype characterized by thick lips, bulbous nose, hypoplasia or absence of nails or terminal phalanges, increased joint mobility, hepatosplenomegaly, and mental deficiency, showed hemihyperplasia with enlargement of her external genitalia and ipsilateral segmental hypertrichosis and hyperpigmentation. A type 2 segmental manifestation is possible but not certain. Vascular disorders: In hereditary hemorrhagic telangiectasia (Osler-Rendu-Weber syndrome), one case of type 1 segmental lesions involving the face was reported. On the other hand, a case suggesting type 2 mosaicism in the form of a pronounced linear lesion involving the forehead has likewise been documented. Molecular studies are so far lacking. – Rhodoid nevus syndrome (“capillary malformation-arteriovenous malformation”) is characterized by a familial occurrence of multiple disseminated rhodoid nevi. These circular or oval lesions are often surrounded by an anemic halo. They are caused by RASA1 mutations. A type 2 segmental manifestation occurs rather frequently in the form of arteriovenous malformation with a concomitant large, segmentally arranged form of rhodoid nevus. For this reason, the phenotype had been described under the name “capillary malformation-arteriovenous malformation”, but it is now clear that the presence of an arteriovenous malformation is by no means a prerequisite for the diagnosis of the syndrome. Blistering skin disorders: Within the group of epidermolysis bullosa, revertant mosaicism is frequently noted, whereas reports on forward mosaicism are virtually absent. Two exceptional cases were found in the literature. – A self-limited form of dystrophic epidermolysis bullosa (“transient bullous dermolysis of the newborn”) is caused by COL7A1 mutations. It tends to heal spontaneously. A female neonate had linear lesions involving one of her legs, giving rise to scarring. Analysis of blood DNA revealed compound heterozygosity at COL7A1, without presence of mosaicism. Skin samples were not available for analysis, which is why the cause of this particular form of cutaneous mosaicism remains unknown. – Another peculiar mosaic phenotype in the form of superficial acantholysis arranged along Blaschko’s lines was reported by Jokiaho et al. (1989) under the term “miliaria rubra-like lesions” in a newborn girl with dysmorphism and a parietal meningocele. The linear acantholytic disorder resolved spontaneously within one week.