Segmental forms of autosomal dominant skin disorders: different types of severity reflect different states of zygosity

Genetic Testing in CYLD Cutaneous Syndrome: An Update

CYLD cutaneous syndrome (CCS) is an inclusive label for the inherited skin adnexal tumour syndromes Brooke–Spiegler Syndrome (BSS-OMIM 605041), familial cylindromatosis (FC – OMIM 132700) and multiple familial trichoepitheliomas (MFT-OMIM 601606). All three syndromes arise due to germline pathogenic variants in CYLD, a tumour suppressor gene (OMIM 605018). CCS is transmitted in an autosomal dominant pattern, and has variable expressivity, both of the three syndromic phenotypes, and of the severity of tumour burden. Age-related penetrance figures are not precisely reported. The first tumours typically appear during puberty and progressively accumulate through adulthood. Penetrance is typically high, with equal numbers of males and females affected. Genetic testing is important for confirmation of the clinical diagnosis, genetic counselling and family planning, including preimplantation diagnosis. Additionally, identified CCS patients may be eligible for future clinical trials of non-surgical pre-emptive interventions that aim to prevent tumour growth. In this update, we review the clinical presentations of germline and mosaic CCS. An overview of the germline pathogenic variant spectrum of patients with CCS reveals more than 100 single nucleotide variants and small insertions and deletions in coding exons, most frequently resulting in predicted truncation. In addition, a minority of patients have large deletions involving the CYLD gene, intronic pathogenic variants that affect splicing, or inversions. We discuss germline and somatic testing approaches. Somatic testing of tumour tissue, relevant in mosaic CCS, can reveal recurrently detected pathogenic variants when two or more tumours are tested. This can influence genetic testing of children, who may inherit this as a germline variant, and inform genetic counselling and prenatal diagnosis. Finally, we discuss testing technologies that are currently used, their benefits and limitations, and future directions for genetic testing in CCS.

Progressive Osseous Heteroplasia is not an Autosomal Dominant Trait but Reflects Superimposed Mosaicism in Different GNAS Inactivation Disorders

Progressive osseous heteroplasia (POH) is a rarely occurring genetic condition characterized by severe segmental ossification involving the skin and deep connective tissues including the muscles. So far, the disorder is generally described as an autosomal dominant trait. By contrast, the following arguments are in favor of the alternative concept that POH should rather be taken as a non-specific segmental manifestation of different GNAS inactivation disorders such as Albright hereditary osteodystrophy (AHO) with hormone resistance, AHO without hormone resistance, and osteomatosis cutis. Presently, POH has got its own OMIM number 166350 but this is obviously wrong because the disorder does not reflect heterozygosity for a GNAS mutation. Conversely, the disorder is most likely due to an early event of postzygotic loss of heterozygosity with loss of the corresponding wild-type allele. This alternative concept, as proposed in 2016, offers a plausible explanation for the following features of POH. Familial occurrence is usually absent. POH is usually observed in families with one of the three GNAS inactivation disorders as mentioned above. Mosaicism is suggested by the pronounced segmental manifestation of POH and by its lateralization. Some patients have, in addition to POH, bilaterally disseminated features of osteomatosis cutis or AHO, and other patients have family members with one of these nonsegmental disorders. Remarkably, POH tends to appear much earlier than the nonsegmental GNAS inactivation disorders. - Molecular support of the concept was documented in a superficial variant of POH called 'plate-like osteoma cutis'. In several other autosomal dominant skin disorders, molecular corroboration of the theory of superimposed mosaicism has been provided. - For all of these reasons, it is unlikely that POH can further be taken as a distinct autosomal dominant trait. Generation of more molecular data in multiple cases of POH occurring in GNAS inactivation disorders will be crucial to corroborate the proposed concept.

Introduction to phacomatoses (neurocutaneous disorders) in childhood

The Dutch ophthalmologist, Jan van der Hoeve, first introduced the terms phakoma/phakomata (from the old Greek word "ϕαχοσ" = lentil, spot, lens-shaped) to define similar retinal lesions recorded in tuberous sclerosis (1920) and in neurofibromatosis (1923). He later applied this concept: (a) to similar lesions in other organs (e.g. brain, heart and kidneys) (1932) and (b) to other disorders (i.e. von Hippel-Lindau disease and Sturge-Weber syndrome) (1933), and coined the term phakomatoses. At the same time, the American neurologist Paul Ivan Yakovlev and psychiatrist Riley H. Guthrie (1931) established the key role of nervous systems and skin manifestations in these conditions and proposed to name them neurocutaneous syndromes (or ectodermoses, to explain the pathogenesis). The Belgian pathologist, Ludo van Bogaert, came to similar conclusions (1935), but used the term neuro-ectodermal dysplasias. In the 1980s, the American paediatric neurologist Manuel R. Gomez introduced the concept of "hamartia/hamartoma" instead of phakoma/phakomata. "Genodermatoses" and "neurocristopathies" were alternative terms still used to define these conditions. Nowadays, however, the most acclaimed terms are "phacomatoses" and "neurocutaneous disorders", which are used interchangeably. Phacomatoses are a heterogeneous group of conditions (mainly) affecting the skin (with congenital pigmentary/vascular abnormalities and/or tumours), the central and peripheral nervous system (with congenital abnormalities and/or tumours) and the eye (with variable abnormalities). Manifestations may involve many other organs or systems including the heart, vessels, lungs, kidneys and bones. Pathogenically, they are explained by interplays between intra- and extra-neuronal signalling pathways encompassing receptor-to-protein and protein-to-protein cascades involving RAS, MAPK/MEK, ERK, mTOR, RHOA, PI3K/AKT, PTEN, GNAQ and GNA11 pathways, which shed light also to phenotypic variability and overlapping. We hereby review the history, classification, genomics, clinical manifestations, diagnostic criteria, surveillance protocols and therapies, in phacomatoses: (1) predisposing to development of tumours (i.e. the neurofibromatoses and allelic/similar disorders and schwannomatosis; tuberous sclerosis complex; Gorlin-Goltz and Lhermitte-Duclos-Cowden syndromes); (2) with vascular malformations (i.e. Sturge-Weber and Klippel-Trenaunay syndromes; megalencephaly/microcephaly-capillary malformation syndromes; CLOVES, Wyburn-Mason and mixed vascular nevus syndromes; blue rubber bleb nevus syndrome; hereditary haemorrhagic telangiectasia); (3) with vascular tumours (von Hippel-Lindau disease; PHACE(S)); (4) with pigmentary/connective tissue mosaicism (incontinentia pigmenti; pigmentary/Ito mosaicism; mTOR-related megalencephaly/focal cortical dysplasia/pigmentary mosaicism; RHOA-related ectodermal dysplasia; neurocutaneous melanocytosis; epidermal/papular spilus/Becker nevi syndromes; PENS and LEOPARD syndromes; encephalocraniocutaneous lipomatosis; lipoid proteinosis); (5) with dermal dysplasia (cerebellotrigeminal dermal dysplasia); and (6) with twin spotting or similar phenomena (phacomatosis pigmentovascularis and pigmentokeratotica; and cutis tricolor).

Neurocutaneous melanocytosis (melanosis)

Neurocutaneous melanosis (NCM; MIM # 249400; ORPHA: 2481], first reported by the Bohemian pathologist Rokitansky in 1861, and now more precisely defined as neurocutaneous melanocytosis, is a rare, congenital syndrome characterised by the association of (1) congenital melanocytic nevi (CMN) of the skin with overlying hypertrichosis, presenting as (a) large (LCMN) or giant and/or multiple (MCMN) melanocytic lesions (or both; sometimes associated with smaller "satellite" nevi) or (b) as proliferative melanocytic nodules; and (2) melanocytosis (with infiltration) of the brain parenchyma and/or leptomeninges. CMN of the skin and leptomeningeal/nervous system infiltration are usually benign, more rarely may progress to melanoma or non-malignant melanosis of the brain. Approximately 12% of individuals with LCMN will develop NCM: wide extension and/or dorsal axial distribution of LCMN increases the risk of NCM. The CMN are recognised at birth and are distributed over the skin according to 6 or more patterns (6B patterns) in line with the archetypical patterns of distribution of mosaic skin disorders. Neurological manifestations can appear acutely in infancy, or more frequently later in childhood or adult life, and include signs/symptoms of intracranial hypertension, seizures/epilepsy, cranial nerve palsies, motor/sensory deficits, cognitive/behavioural abnormalities, sleep cycle anomalies, and eventually neurological deterioration. NMC patients may be symptomatic or asymptomatic, with or without evidence of the typical nervous system changes at MRI. Associated brain and spinal cord malformations include the Dandy-Walker malformation (DWM) complex, hemimegalencephaly, cortical dysplasia, arachnoid cysts, Chiari I and II malformations, syringomyelia, meningoceles, occult spinal dysraphism, and CNS lipoma/lipomatosis. There is no systemic involvement, or only rarely. Pathogenically, single postzygotic mutations in the NRAS (neuroblastoma RAS viral oncogene homologue; MIM # 164790; at 1p13.2) proto-oncogene explain the occurrence of single/multiple CMNs and melanocytic and non-melanocytic nervous system lesions in NCM: these disrupt the RAS/ERK/mTOR/PI3K/akt pathways. Diagnostic/surveillance work-ups require physical examination, ophthalmoscopy, brain/spinal cord magnetic resonance imaging (MRI) and angiography (MRA), positron emission tomography (PET), and video-EEG and IQ testing. Treatment strategies include laser therapy, chemical peeling, dermabrasion, and surgical removal/grafting for CMNs and shunt surgery and surgical removal/chemo/radiotherapy for CNS lesions. Biologically targeted therapies tailored (a) BRAF/MEK in NCM mice (MEK162) and GCMN (trametinib); (b) PI3K/mTOR (omipalisib/GSK2126458) in NMC cells; (c) RAS/MEK (vemurafenib and trametinib) in LCMNs cells; or created experimental NMC cells (YP-MEL).

The concept of type 2 segmental mosaicism, expanding from dermatology to general medicine

In autosomal dominant skin disorders, the well-known type 1 segmental mosaicism reflects heterozygosity for a postzygotic new mutation. By contrast, type 2 segmental mosaicism originates in a heterozygous embryo from an early postzygotic mutational event giving rise to loss of the corresponding wild-type allele, which results in a pronounced segmental involvement being superimposed on the ordinary, non-segmental phenotype. Today, this concept has been proven by molecular analysis in many cutaneous traits. The purpose of this review was to seek publications of cases suggesting an extracutaneous manifestation of type 2 segmental mosaicism. Case reports documenting a pronounced extracutaneous segmental involvement were collected from the literature available in PubMed and from personal communications to the author. Pertinent cases are compared to the description of cutaneous segmental mosaicism of type 1 or type 2 as reported in a given trait. In total, reports suggesting extracutaneous type 2 segmental mosaicism were found in 14 different autosomal dominant skin disorders. In this way, clinical evidence is accumulated that extracutaneous type 2 segmental mosaicism does likewise occur in many autosomal dominant skin disorders. So far, however, molecular proof of this particular form of mosaicism is lacking. The present review may stimulate readers to inform colleagues of other specialties on this new concept, in order to initiate further research in this particular field of knowledge that has important implications for diagnosis, treatment and genetic counselling.

Early history of the different forms of neurofibromatosis from ancient Egypt to the British Empire and beyond: First descriptions, medical curiosities, misconceptions, landmarks, and the persons behind the syndromes

The earliest examples of neurofibromatosis (in this case type 1, NF1) can be traced in the Ebers Papyrus (Ancient Egypt, 1.500 B.C.), in a Hellenistic statuette (Smyrna, 323 B.C.), in the coinage of the Parthians kings (247 B.C.) and in some 13th century monks' drawings. These earlier examples are somewhat less well defined as compared to the most recent better defined reports credited as having NF1 including an Inca child mummy (1480-1650 AD), Ulisse Aldrovandi's homuncio ("Monstrorum Historia", 1592 A.D.) with mosaic NF1 or the illustrations seen in the 18th century "Buffon's Histoire Naturelle" and "Cruveilhier's Anatomie Pathologique du Corps Human". The first English language report on NF1 was made by Akenside in 1768 and the first systematic review by Robert William Smith in 1849, while Virchow's pupil, Friedrich Daniel von Recklinghausen, in 1882, was the first to understand the origin of skin tumors and to name them neurofibromas. The touching story of Joseph C. Merrick (the "Elephant man," (who had Proteus syndrome and not NF1), in 1884, played an important role in the later misconception of NF1, as did the novel by Vicotr Hugo on the hunchback Quasimodo. The studies by van der Hoeve (1921), Yakovlev and Guthrie (1931), and Van Bogaert (1935), categorized "von Recklinghausen's" neurofibromatosis among the phakomatoses and the neurocutaneous syndromes. The first known mention of an acoustic neuroma (at autopsy) is attributed to Eduard Sandifort (1777 AD) while John H. Wishart made the earliest autoptic description of neurofibromatosis type 2 (NF2), in 1822, in a 21-year-old man with bilateral acoustic neuromas, who manifested signs since his infancy (Wishart subtype NF2). Smith likely described the first case of schwannomatosis in 1849. Older, Virchow, von Recklinghausen, and Verocay first classified "neuromas" and Masson and Penfield first used the word "schwannoma" taking it from Theodore Schwann's works. In 1903 Henneberg and Koch described NF2 in detail. Young, Eldridge, and Gardner, in the late '70, established NF2 as a distinct familial entity (Gardner subtype NF2). Schwannomatosis, the late entry of the different forms of neurofibromatosis, was credited in the middle '90.

Mosaic Neurocutaneous Disorders and Their Causes

Neurocutaneous disorders are a heterogeneous group of conditions (mainly) affecting the skin [with pigmentary/vascular abnormalities and/or cutaneous tumours] and the central and peripheral nervous system [with congenital abnormalities and/or tumours]. In a number of such disorders, the skin abnormalities can assume a mosaic patterning (usually arranged in archetypical patterns). Alternating segments of affected and unaffected skin or segmentally arranged patterns of abnormal skin often mirror similar phenomena occurring in extra-cutaneous organs/tissues [eg, eye, bone, heart/vessels, lung, kidney and gut]. In some neurocutaneous syndromes the abnormal mosaic patterning involve mainly the skin and the nervous system configuring a (true) mosaic neurocutaneous disorder; or an ordinary trait of a neurocutaneous disorder is sometimes superimposed by a pronounced linear or otherwise segmental involvement; or, lastly, a neurocutaneous disorder can occur solely in a mosaic pattern. Recently, the molecular genetic and cellular bases of an increasing number of neurocutaneous disorders have been unravelled, shedding light on the interplays between common intra- and extra-neuronal signalling pathways encompassing receptor-protein and protein-to-protein cascades (eg, RAS, MAPK, mTOR, PI3K/AKT and GNAQ pathways), which are often responsible of the mosaic distribution of cutaneous and extra-cutaneous features. In this article we will focus on the well known, and less defined mosaic neurocutaneous phenotypes and their related molecular/genetic bases, including the mosaic neurofibromatoses and their related forms (ie, spinal neurofibromatosis and schwannomatosis); Legius syndrome; segmental arrangements in tuberous sclerosis; Sturge-Weber and Klippel-Trenaunay syndromes; microcephaly/megalencephaly-capillary malformation; blue rubber bleb nevus syndrome; Wyburn-Mason syndrome; mixed vascular nevus syndrome; PHACE syndrome; Incontinentia pigmenti; pigmentary mosaicism of the Ito type; neurocutaneous melanosis; cutis tricolor; speckled lentiginous syndrome; epidermal nevus syndromes; Becker's nevus syndrome; phacomatosis pigmentovascularis and pigmentokeratotica; Proteus syndrome; and encephalocraniocutaneous lipomatosis.

Patterned disorders in dermatology

The skin gives us an opportunity to study pathologies unapparent in other systems such as patterned disorders. Among the best-identified patterns of skin disorders are the well-known lines of Blaschko, but other types of skin-patterned lesions have also been recognized. This short review will describe and discuss these different patterns and their pathophysiologic mechanisms, such as somatic mosaicism and X-chromosome associated mosaicism. Cutaneous patterned disorders are thought to be associated usually with inherited diseases per se, but in fact they are also reported in so-called acquired diseases. These cases suggest the existence of an underlying defect in a gene closely associated with the disease pathogenesis. The study of these acquired patterned disorders in the future may help us to understand the biologic foundations and pathogenesis of common human diseases.

Cutaneous mosaicism: a molecular and clinical review

Physicians have long been intrigued by the distinct patterns created by epidermal nevi and other mosaic cutaneous disorders. Although many of the molecular mechanisms underlying these disorders remain unrevealed, with the release of the results of the Human Genome Project our knowledge is rapidly increasing. The underlying genetic defects for many of the X-linked and mosaic disorders have recently been identified. Advances in technology, such as the array comparative genomic hybridization, will provide the tools for continued gene discovery and expanded understanding of the pathogenic mechanisms underlying mosaic skin conditions.

Melorheostosis: case report with 20-year follow-up

The authors report on a typical case of melorheostosis observed in an 18-year-old man, localized in the II digit of the right hand causing tumefaction and irregular pain. At 20-year follow-up, the patient showed a radiographical slight worsening of the lesion. Radiographic examination showed a mild increase in cortical and endosteal hyperostosis with bone shape alteration in the II digit of the right hand, slight cortical and endosteal hyperostosis at the level of right shoulder girdle involving the humerus. The other part of the skeleton was not affected. Clinical examination revealed swelling and tumefaction of the forefinger of the right hand and reduced articular motion both in proximal and distal interphalangeal joint and metacarpal phalangeal joint. The reminder of the clinical examination was normal. Melorheostosis is an uncommon mesenchymal disorder characterized by a chondral hyperostosis of the long bones associated to a sclerosis of the spongious bone. The etiology of this affection is unknown: the most accredited hypothesis is a developmental anomaly with a sequential sclerotomes distribution. Both genders may be affected, with the long tubular bones of the lower limbs more involved. This anomaly is often asymptomatic but maybe accompanied by pain with a smooth symptom progression and periodic exacerbations. Therapy is mainly symptomatic and comprises anti-inflammatory drugs or surgical approach for removal of soft tissue that may preclude daily activities. This case report demonstrates that melorheostosis is a relatively benign disorder with mildly progressive course.

Cutaneous mosaicism: right before our eyes

Autosomal recessive cutaneous disorders, including various types of epidermolysis bullosa (EB), usually manifest shortly after birth. The clinical course of these diseases is often characterized by severe complications, limited therapeutic options, and a poor prognosis. A study by Pasmooij et al. reported in this issue of the JCI unravels the molecular mechanisms by which germline mutations in non-Herlitz junctional EB can be corrected in vivo by multiple spontaneously occurring somatic mutational events, a phenomenon known as revertant mosaicism (see the related article beginning on page 1240). These insights open new avenues of thinking for the design of future gene therapy strategies for skin diseases.

Segmental overgrowth, lipomatosis, arteriovenous malformation and epidermal nevus (SOLAMEN) syndrome is related to mosaic PTEN nullizygosity

We describe two patients from distinct Cowden disease families with specific germline PTEN mutations whose disease differs from the usual appearance of Cowden disease. Their phenotype associates classical manifestations of Cowden disease and congenital dysmorphisms including segmental overgrowth, arteriovenous and lymphatic vascular malformations, lipomatosis and linear epidermal nevus reminiscent of the diagnosis of Proteus syndrome. We provide evidence in one of the two patients of a secondary molecular event: a loss of the PTEN wild-type allele, restricted to the atypical lesions that may explain an overgrowth of the affected tissues and the atypical phenotype. These data provide a new demonstration of the Happle hypothesis to explain some segmental exacerbation of autosomal-dominant disorders. They also show that a bi-allelic inactivation of PTEN can lead to developmental anomalies instead of malignant transformation, thus raising the question of the limitations of the tumor suppressive function in this gene. Finally, we suggest using the term 'SOLAMEN syndrome' (Segmental Overgrowth, Lipomatosis, Arteriovenous Malformation and Epidermal Nevus) in these peculiar situations to help the difficult distinction between the phenotype of our patients and Proteus syndrome.

The acanthosis nigricans form of epidermal nevus

We observed 4 individuals with the acanthosis nigricans (AN) form of epidermal nevus, with clinical and histopathologic features of AN oriented along Blaschko's lines. Three patients had stable lesions since childhood. One patient concurrently had typical bilateral AN lesions. This condition may represent a mosaic form of AN.

Atopic dermatitis with increased severity along a line of Blaschko

Several primarily symmetric skin diseases may, on rare occasions, manifest themselves more prominently along the embryonic migration pathways of cutaneous cell clones. Loss of heterozygosity along these lines of Blaschko resulting in hemizygosity or homozygosity of alleles predisposing for the disease is the most likely explanation for this phenomenon. Here, we report a case of severe Blaschko linear atopic dermatitis superimposed on a milder symmetric eruption of atopic eczema in a 36-year-old man with personal and familial history of allergy. Continuous transition of linear atopic eczema to linear vesicular (dyshidrotic) plantar eczema demonstrates the relationship between these two entities. Individuals such as our patient offer an opportunity to identify intraindividual genetic variations marking loci involved in the pathogenesis of atopy and atopic eczema.

Agminated acquired melanocytic nevi of the common and dysplastic type

We previously reported a single case of agminated acquired melanocytic nevi, consisting of a localized clustering of banal and atypical moles. We now report 4 more cases, confirming that the initial case was not an isolated finding. We examined the lesions clinically, with a dermoscope, with a Wood's light, and in 3 cases with UV photography so as to exclude nevus spilus from the differential diagnosis. The presence of an underlying dysplastic nevus syndrome phenotype in 4 of the 5 cases raises the possibility that agminated nevi arise as a consequence of postzygotic loss of heterozygosity and, thus, may represent a type 2 segmental manifestation of the atypical mole syndrome phenotype. Further studies of similar cases using microdissection techniques for analysis of loss of heterozygosity pattern are warranted.

Piecing together the puzzle of cutaneous mosaicism

Autosomal dominant disorders of the skin may present in a pattern following the lines of embryologic development of the ectoderm. In these cases, the surrounding skin is normal, and molecular studies have shown that the causative mutation is confined to the affected ectodermal tissue (type 1 mosaicism). Rarely, an individual shows skin lesions that follow the pattern of type 1 mosaicism, but the rest of the skin shows a milder form of the disorder (type 2 mosaicism). A new study provides the molecular basis for type 2 mosaicism.

Allelic loss underlies type 2 segmental Hailey-Hailey disease, providing molecular confirmation of a novel genetic concept

Hailey-Hailey disease (HHD) is an autosomal dominant trait characterized by erythematous and oozing skin lesions preponderantly involving the body folds. In the present unusual case, however, unilateral segmental areas along the lines of Blaschko showing a rather severe involvement were superimposed on the ordinary symmetrical phenotype. Based on this observation and similar forms of mosaicism as reported in other autosomal dominant skin disorders, we postulated that in such cases, 2 different types of segmental involvement can be distinguished. Accordingly, the linear lesions as noted in the present case would exemplify type 2 segmental HHD. In the heterozygous embryo, loss of heterozygosity occurring at an early developmental stage would have given rise to pronounced linear lesions reflecting homozygosity or hemizygosity for the mutation. By analyzing DNA and RNA derived from blood and skin samples as well as keratinocytes of the index patient with various molecular techniques including RT-PCR, real-time PCR, and microsatellite analysis, we found a consistent loss of the paternal wild-type allele in more severely affected segmental skin regions, confirming this hypothesis for the first time, to our knowledge, at the molecular and cellular level.

Maladie de Darier linéaire dans une fratrie

BACKGROUND

Darier's disease or keratosis follicularis is an autosomal dominant acantholytic disorder that frequently arises as a result of spontaneous mutation. It is either a generalized or localized condition due to a mutation in the SERCA2 12q23-q24,1 resulting in a faulty organization of the tonofilaments. We present two siblings affected with the linear form of this disorder and discuss these cases as an example of the genetic mechanism of loss of heterozygosity.

CASE REPORTS

A 7 year-old girl was referred for evaluation of linear lesions present since the first year of age. Examination disclosed red, 1 to 2 mm papules that coalesced to form linear plaques on the left side of the vulvar and perianal areas, and on the left hand and foot. Her older brother had similar lesions in a linear arrangement on the left side of the face neck and homolateral foot. No lesions were found in their parents. Biopsies of both affected children revealed an intraepidermal suprabasal cleft. Dyskeratotic cells were present in the spinous layer, and corps ronds and grains near the granular layer.

DISCUSSION

The linear form of Darier's disease could result from genetic mosaicism for this autosomal dominant disorder. As these children have a more pronounced involvement than the usual Darier's disease lesions, disposed in a linear arrangement, they probably represent a type 2 segmental manifestation of the disorder. Likewise, the presence of the same linear disorder in two siblings could be explained by loss of heterozygosity for the Darier's disease gene.

Melorheostosis may originate as a type 2 segmental manifestation of osteopoikilosis

Melorheostosis is a non-hereditary disorder involving the bones in a segmental pattern, whereas osteopoikilosis is a rather mild disseminated bone disorder inherited as an autosomal dominant trait. Interestingly, melorheostosis and osteopoikilosis may sometimes occur together. In analogy to various autosomal dominant skin disorders for which a type 2 segmental manifestation has been postulated, melorheostosis may be best explained in such cases as a type 2 segmental osteopoikilosis, resulting from early loss of the corresponding wild type allele at the gene locus of this autosomal dominant bone disorder.

Buschke-ollendorff syndrome: report of a case and interpretation of the clinical phenotype as a type 2 segmental manifestation of an autosomal dominant skin disease

Buschke-Ollendorff syndrome is a rare, autosomal dominant disease consisting of osteopoikilosis and skin manifestations. A case is reported, and the literature is reviewed with special reference to the clinical distribution patterns of skin lesions. The 2 main types of skin manifestations in this entity are widely disseminated, symmetrically distributed papules and localized, asymmetrically distributed plaques. Both types of lesions have been observed within the same family or within the same person. This particular phenotype can be explained by type 2 segmental manifestation of an autosomal dominant cutaneous trait: Symmetrically distributed papules are a manifestation of the heterozygous state acquired by inheritance, and asymmetrically distributed plaques develop in areas that have undergone a somatic mutational event of the wild-type allele at an early developmental stage, the result being loss of heterozygosity.

Type 2 segmental manifestation of congenital multiple glomangiomas

Congenital multiple glomus tumors are extremely rare, and less than 20 cases have been well documented. We report an uncommon case of congenital multiple glomangiomas with a segmental manifestation in a 9-year-old girl. Since birth, the child had presented asymptomatic angiomatous macules arranged in a segmental pattern on the neck and trunk. During a follow-up period of 9 years, disseminated smaller papulonodular lesions developed on both arms and the left leg with a segmental distribution. Histopathology of congenital and acquired lesions confirmed the diagnosis of glomangiomas. The family history was negative for glomus tumors. This type of presentation supports the recently described type 2 segmental manifestation of multiple glomus tumors, with a segmental involvement of congenital early developing lesions.

Delineation of a newly recognized neurocutaneous malformation syndrome with "cutis tricolor"

The term "cutis tricolor" describes the combination of congenital hyper- and hypo-pigmented lesions, in close proximity to each other with a background of normal skin. Cutis tricolor represents twin spotting and has been reported as an isolated skin disorder or as part of a neurocutaneous malformation syndrome. We report on an 11-year-old girl with diffuse pigmentary changes of the cutis tricolor type, facial anomalies, mental retardation, epileptic seizures, EEG anomalies, small skull, progressive double-curved thoracolumbar/lumbar scoliosis with vertebral scalloping and dysplastic vertebral pedicles and ribs, and tibial bowing. These abnormalities are similar to those observed in cases reported by Happle et al. [1997: J Med Genet 34:676-678] and Ruggieri [2000: Eur J Pediatr 159:745-749]. Additionally, our patient had altered behavior and hypoplasia of the corpus callosum. This constellation of abnormalities represents a newly recognized neurocutaneous malformation syndrome. The phenotype could be explained by somatic mutation. Loss of heterozygosity at an early developmental stage would give rise to one single mosaic skin disorder (e.g., generalized skin manifestations of the cutis tricolor type in association to extracutaneous anomalies). Postzygotic recombination occurring later during embryogenesis would give rise to solitary lesions confined to the skin.

Cutaneous leiomyomatosis with type 2 segmental involvement

A 21-year-old man had histologically-confirmed diffuse cutaneous leiomyomatosis. The lesions showed a peculiar distribution in that they predominantly involved several segments of the right side of his body; in addition, less extensive, nonsegmental lesions were present on both sides of the body. Although this case was apparently sporadic, the genetic mechanism of loss of heterozygosity provides a plausible explanation for this unusual presentation. If the patient were heterozygous for the underlying mutation, at an early developmental stage a postzygotic event of loss of heterozygosity would have given rise to a type 2 segmental involvement, resulting in pronounced lesions superimposed on the disseminated tumors of the ordinary phenotype.

Nonsyndromic type of hereditary multiple basal cell carcinoma

An autosomal dominant phenotype characterized by multiple superficial basal cell carcinomas (BCC) without associated anomalies is postulated on the ground of the following data. There are several reports on multiple BCC occurring in two generations of a family, including male-to-male transmission. There are also three reports of a strictly unilateral manifestation of multiple superficial BCC, suggesting mosaicism. The father of one of the patients with unilateral involvement was affected with multiple disseminated BCC, which suggests a type 2 segmental manifestation in the son, reflecting loss of heterozygosity that occurred at an early stage of embryogenesis. The three cases of unilateral arrangement would be difficult to explain without the assumption that multiple nonsyndromic superficial BCC may occur as a distinct mendelian trait.

Two cases of segmental multiple glomangiomas in a family: type 1 or type 2 segmental manifestation?

Several autosomal dominant skin diseases may manifest cutaneous mosaicism. Two types of segmental arrangement can be distinguished: type 1 is characterized by segmental lesions with similar severity to that observed in the diffuse phenotype, the remaining skin being normal; type 2 is characterized by segmental lesions showing a major degree of severity and milder lesions diffusely arranged. Multiple glomus tumours have recently been included in the group of genodermatoses showing type 2 segmental involvement. A family with 2 cases of multiple glomangiomas arranged in a segmental fashion is reported. A 12-year-old girl presented multiple nodular glomangiomas on her right buttock and thigh, in a band-like distribution. A sister of her paternal grandfather showed plaque-like multiple glomangiomas on her left thigh and various glomangiomas on her right buttock and arm. No other family members were known to be affected. Two new cases of familial segmental multiple glomangiomas are reported, with the particularity that one of these exhibited type 2 segmental manifestation and the other type 1 from a clinical point of view.

Three cases of type 2 segmental manifestation of multiple glomus tumors: association with linear multiple trichilemmal cysts in a patient

We report 3 cases of congenital multiple glomus tumors seen during the last 5 years. One of them showed autosomal dominant inheritance with male-to-male transmission. The remaining patients had no family history of similar lesions. The clinical and histopathological aspects of our patients support the recently described type 2 segmental manifestation of multiple glomus tumors. One of the cases showed associated multiple and giant trichilemmal cysts with a linear distribution in the scalp.

Loss of heterozygosity in human skin

Loss of heterozygosity (LOH) is a genetic mechanism by which a heterozygous somatic cell becomes either homozygous or hemizygous because the corresponding wild-type allele is lost. LOH has today been recognized as a major cause of malignant growth. This article gives a comprehensive review of skin disorders in which an origin from LOH has been either documented at the molecular level or postulated on the basis of clinical evidence. LOH has been shown to cause basal cell carcinoma, squamous cell carcinoma, and malignant melanoma, but this mechanism can likewise be taken as an important model to explain the origin of many other skin diseases such as benign hamartomas; type 2 segmental manifestation of autosomal dominant skin disorders; a pronounced segmental manifestation of acquired skin disorders with a polygenic background, superimposed on symmetric lesions of the usual type; paired mutant patches in the form of either allelic or nonallelic twin spotting; and the exceptional familial occurrence of some nevi, reflecting paradominant transmission. completion of this learning activity, readers should be familiar with the mechanism of LOH and its general significance for the biology of plants, animals, and humans. Participants should understand that this mechanism plays a crucial role not only in cutaneous malignant growth but also in the development of benign skin disorders, and they should be able to examine such diseases with a prepared mind to gain a better understanding of their origin.

Type 2 segmental manifestation of multiple glomus tumors: A review and reclassification of 5 case reports

BACKGROUND

In various autosomal dominant skin disorders, segmental forms reflecting mosaicism have been reported. Recently, two different types of mosaic manifestation have been delineated. Type 1 reflects heterozygosity for the underlying mutation and shows a degree of severity as observed in the corresponding nonmosaic phenotype. Type 2 originates from loss of heterozygosity, shows an excessively severe involvement and is usually superimposed on the disseminated lesions of the ordinary trait.

OBJECTIVE

We wanted to exemplify further the proposed rule of dichotomy.

METHODS

We have screened the literature on multiple glomus tumors, a trait that follows an autosomal dominant mode of transmission.

RESULTS

We found 5 cases of multiple glomus tumors suggesting a type 2 segmental involvement. In all of these cases, a unilateral band-like or patchy arrangement of excessively pronounced glomus tumors was associated with disseminated lesions corresponding to the ordinary phenotype, and in 3 cases other family members were affected with disseminated glomus tumors. The unilateral agminated lesions were reported to be present in early childhood, whereas the disseminated lesions appeared later.

CONCLUSION

Multiple glomus tumors can be added to the list of autosomal dominant skin disorders that may show a type 2 segmental involvement.