Genotype-phenotype correlations emerging from the identification of missense mutations in MBTPS2.

Missense mutations affecting membrane-bound transcription factor protease site 2 (MBTPS2) have been associated with Ichthyosis Follicularis with Atrichia and Photophobia (IFAP) syndrome with or without BRESHECK syndrome, with keratosis follicularis spinulosa decalvans, and Olmsted syndrome. This metalloprotease activates, by intramembranous trimming in conjunction with the protease MBTPS1, regulatory factors involved in sterol control of transcription and in cellular stress response. In this study, 11 different MBTPS2 missense mutations detected in patients from 13 unrelated families were correlated with the clinical phenotype, with their effect on cellular growth in media without lipids, and their potential role for sterol control of transcription. Seven variants were novel [c.774C>G (p.I258M); c.758G>C (p.G253A); c.686T>C (p.F229S); c.1427T>C (p.L476S); c.1430A>T (p.D477V); c.1499G>A (p.G500D); c.1538T>C (p.L513P)], four had previously been reported in unrelated sibships [c.261G>A (p.M87I); c.1286G>A (p.R429H); c.1424T>C (p.F475S); c.1523A>G (p.N508S)]. In the enzyme, the mutations cluster in transmembrane domains. Amino-acid exchanges near the active site are more detrimental to functionality of the enzyme and, clinically, associated with more severe phenotypes. In male patients, a genotype-phenotype correlation begins to emerge, linking the site of the mutation in MBTPS2 with the clinical outcome described as IFAP syndrome with or without BRESHECK syndrome, keratosis follicularis spinulosa decalvans, X-linked, Olmsted syndrome, or possibly further X-linked traits with an oculocutaneous component.

Smoker's boils.

BACKGROUND: About 90% of patients with hidradenitis suppurativa (HS) are smokers. A crucial eliciting role of smoking appears to be certain. In order to increase the awareness of this avoidable major cause of the disease and to facilitate the recognition of incipient disorder, we propose the more specific term 'smoker's boils' for HS lesions of patients who are smokers. METHOD: Clinical pictures of early lesions are presented. For the exceptional cases occurring in nonsmokers, the traditional name HS, representing an umbrella term, is adequate. RESULT/CONCLUSION: The renaming of HS as smoker's boils has the practical advantage that a correct diagnosis can be made at an incipient stage of the disorder. If patients stop smoking at such an early stage of HS, they most likely have a chance that this devastating disease will not progress.

Intronic mutations affecting splicing of MBTPS2 cause ichthyosis follicularis, alopecia and photophobia (IFAP) syndrome.

Ichthyosis follicularis, alopecia and photophobia (IFAP) syndrome is an X-linked genodermatosis with congenital atrichia being the most prominent feature. Recently, we have shown that functional deficiency of MBTPS2 (membrane-bound transcription factor protease site 2) - a zinc metalloprotease essential for cholesterol homeostasis and endoplasmic reticulum stress response - causes the disease. Here, we present results obtained by analysing two intronic MBTPS2 mutations, c.671-9T>G and c.225-6T>A, using in silico and cell-based splicing assays. Accordingly, the c.225-6T>A transversion generated a new splice acceptor site, which caused extension of exon 3 by four bases and subsequently introduced a premature stop codon. Both, minigene experiments and RT-PCR analysis with patient-derived mRNA, demonstrated that the c.671-9T>G mutation resulted in skipping of exon 6, most likely because of disruption of the polypyrimidin tract or a putative intronic splicing enhancer (ISE). Our combined biocomputational and experimental analysis strongly suggested that both intronic alterations are disease-causing mutations.

Donor dominance cures CHILD nevus.

BACKGROUND: Congenital hemidysplasia with ichthyosiform nevus and limb defects (MIM 308050, CHILD) syndrome is an X-linked dominant, male-lethal, multisystem birth defect. Patients suffer from an inflammatory nevus that covers large areas, predominantly of one side of the body, with a sharp midline demarcation. Treatment of CHILD nevus is notoriously difficult. OBJECTIVE: The aim of this study was to develop a novel surgical approach for this disorder. METHODS: In 2 patients, the CHILD nevus was dermabraded, and the area was covered with split skin grafts obtained from a contralateral unaffected donor region. In a third patient, papillomatous, strawberry-like lesions on fingers and toes were excised, and the defects were covered with full-thickness grafts obtained from the unaffected left, gluteal area. RESULTS: Highly satisfying functional and cosmetic results were documented during a follow-up period ranging from 3 to 8 years. CONCLUSION: The favorable outcome, superior to that obtained by simple dermabrasion or extensive plastic surgery, can best be explained by the donor dominance of the grafted skin samples that carried, in all or most cells, the mutant X chromosome in an inactivated form.

IFAP syndrome is caused by deficiency in MBTPS2, an intramembrane zinc metalloprotease essential for cholesterol homeostasis and ER stress response.

Ichthyosis follicularis with atrichia and photophobia (IFAP syndrome) is a rare X-linked, oculocutaneous human disorder. Here, we assign the IFAP locus to the 5.4 Mb region between DXS989 and DXS8019 on Xp22.11-p22.13 and provide evidence that missense mutations exchanging highly conserved amino acids of membrane-bound transcription factor protease, site 2 (MBTPS2) are associated with this phenotype. MBTPS2, a membrane-embedded zinc metalloprotease, activates signaling proteins involved in sterol control of transcription and ER stress response. Wild-type MBTPS2 was able to complement the protease deficiency in Chinese hamster M19 cells as shown by induction of an SRE-regulated reporter gene in transient transfection experiments and by growth of stably transfected cells in media devoid of cholesterol and lipids. These functions were impaired in five mutations as detected in unrelated patients. The degree of diminished activity correlated with clinical severity as noted in male patients. Our findings indicate that the phenotypic expression of IFAP syndrome is quantitatively related to a reduced function of a key cellular regulatory system affecting cholesterol homeostasis and ability to cope with ER stress.

PORCN mutations in focal dermal hypoplasia: coping with lethality.

The X-linked dominant trait focal dermal hypoplasia (FDH, Goltz syndrome) is a developmental defect with focal distribution of affected tissues due to a block of Wnt signal transmission from cells carrying a detrimental PORCN mutation on an active X-chromosome. Molecular characterization of 24 unrelated patients from different ethnic backgrounds revealed 23 different mutations of the PORCN gene in Xp11.23. Three were microdeletions eliminating PORCN and encompassing neighboring genes such as EBP, the gene associated with Conradi-Hünermann-Happle syndrome (CDPX2). 12/24 patients carried nonsense mutations resulting in loss of function. In one case a canonical splice acceptor site was mutated, and 8 missense mutations exchanged highly conserved amino acids. FDH patients overcome the consequences of potentially lethal X-chromosomal mutations by extreme skewing of X-chromosome inactivation in females, enabling transmission of the trait in families, or by postzygotic mosaicism both in male and female individuals. Molecular characterization of the PORCN mutations in cases diagnosed as Goltz syndrome is particularly relevant for genetic counseling of patients and their families since no functional diagnostic test is available and carriers of the mutation might otherwise be overlooked due to considerable phenotypic variability associated with the mosaic status.

A large duplication in LIPH underlies autosomal recessive hypotrichosis simplex in four Middle Eastern families.

Autosomal recessive hypotrichosis simplex (ARHS) manifests with paucity of hair appearing during early childhood. We assessed four affected families. We initially genotyped three of these families for a panel of microsatellite markers spanning all ARHS-associated loci and obtained data suggesting linkage to 3q27, encompassing LIPH, which had previously been shown to be associated with ARHS. Accordingly, a homozygous duplication mutation in exon 2 of this gene (c.280_369dup; p.Gly94_Lys123dup) was found to segregate with the disease in all the families. Through the identification of the first duplication mutation in the human LIPH gene, we provide further evidence supporting a role for the phospholipase signalling pathway in hair growth and differentiation.

Monozygotic twins discordant for Proteus syndrome.

Proteus syndrome is a rare, complex disorder predominantly characterized by asymmetric overgrowth of body parts, connective tissue and epidermal nevi, and vascular malformations. General diagnostic criteria comprise mosaic distribution, sporadic occurrence, and progressive course. We report on Proteus syndrome in discordant monozygotic twins. The affected 9-year-old boy showed progressive postnatal overgrowth of his right leg and foot and asymmetric progressive overgrowth of single toes with a small cerebriform connective tissue nevus on his right fourth toe. The progressive course was documented by serial photographs over a period of 3 years. Twin monozygosity was determined by PCR-amplified short tandem repeat (STR) analysis, revealing complete concordance of all alleles in both twins. This observation, to our knowledge, is only the second case report of discordant Proteus syndrome in monozygotic twins. This supports the hypothesis that this rare condition is caused by a postzygotic mutational event resulting in mosaicism.

Deficiency of PORCN, a regulator of Wnt signaling, is associated with focal dermal hypoplasia.

Focal dermal hypoplasia (FDH) is an X-linked dominant multisystem birth defect affecting tissues of ectodermal and mesodermal origin. Using a stepwise approach of (i) genetic mapping of FDH, (ii) high-resolution comparative genome hybridization to seek deletions in candidate chromosome areas and (iii) point mutation analysis in candidate genes, we identified PORCN, encoding a putative O-acyltransferase and potentially crucial for cellular export of Wnt signaling proteins, as the gene mutated in FDH. The findings implicate FDH as a developmental disorder caused by a deficiency in PORCN.

Inverse Klippel-Trenaunay syndrome: review of cases showing deficient growth.

BACKGROUND: Klippel-Trenaunay syndrome is defined by a coexistence of nevus flammeus and overgrowth of one or more limbs. Remarkably, however, deficient growth of an affected limb may likewise be noted. OBSERVATIONS: We collected from the literature a number of cases of Klippel-Trenaunay syndrome associated with deficient growth such as shortening or hypoplastic muscle mass of the affected extremity. DISCUSSION: The cause of the unusual deficient growth is unknown. Some patients may be compound heterozygotes carrying a 'plus' and a 'minus' allele at the responsible gene locus, and postzygotic recombination would give rise to two different cell clones homozygous for either allele. CONCLUSION: In order to give a name to such paradoxical cases, we propose the term 'inverse Klippel-Trenaunay syndrome'.

CHILD syndrome in 3 generations: the importance of mild or minimal skin lesions.

BACKGROUND: CHILD syndrome (congenital hemidysplasia with ichthyosiform nevus and limb defects, Online Mendelian Inheritance in Man 308050) is an X-linked dominant trait with lethality for male embryos. The disorder is caused by mutations in NSDHL (Online Mendelian Inheritance in Man 300275), a gene playing an important role in the cholesterol biosynthetic pathway. Most reports deal with sporadic cases, and only 5 cases of mother-to-daughter transmission have been documented. We present here a family with mild features of CHILD syndrome in 3 generations. Molecular analysis was used to confirm the diagnosis. OBSERVATIONS: We studied 14 members of a family with CHILD syndrome. The 23-year-old proposita, her mother, 2 aunts, and her grandmother presented with mild or minimal skin lesions that had been present since infancy. Analysis of the NSDHL gene showed missense mutation c.370G-->A in these 5 patients. This mutation was absent in the 9 clinically unaffected family members tested. CONCLUSIONS: In this family, we recognized CHILD syndrome with mild or minimal features in 3 generations because we were able to verify our clinical diagnosis by means of molecular analysis. We assume that many cases that so far have been considered sporadic may in fact be familial when a meticulous physical examination of female family members is combined with molecular testing.

The expression of the 27-kd heat shock protein in keratinization disorders: an immunohistological study.

In human skin, the 27-kd heat shock protein (hsp27), a member of the small hsp family, is expressed mainly in the upper epidermal layers. Hsp27 functions as a molecular chaperone and is involved in the regulation of cell growth and differentiation. According to experimental evidence, epidermal hsp27, through its chaperone function, might play a role in the assembly of keratin filaments and the cornified cell envelope. This study was conducted to assess the expression pattern of hsp27 in a panel of different ichthyoses. Twelve hereditary and acquired skin diseases associated with an ichthyotic phenotype and 2 corresponding mouse models were investigated by immunohistochemistry on formalin-fixed paraffin-embedded tissue, using a monoclonal antibody specific for hsp27. In ichthyosis vulgaris, lamellar ichthyosis, Sjögren-Larsson syndrome, Netherton syndrome, and acquired ichthyosiform skin condition, the pattern of hsp27 expression resembles healthy human skin. Hsp27 expression was reduced in bullous ichthyosiform erythroderma and annular epidermolytic ichthyosis, and absent in X-linked recessive ichthyosis (1/3 patients) and congenital hemidysplasia with ichthyosiform nevus and limb defects syndrome (1/1). In X-linked dominant chondrodysplasia, 3 small samples are completely negative and 2 larger samples show a pattern resembling random X inactivation. In the mouse models, tattered and bare patches, representing the murine analogues to X-linked dominant chondrodysplasia and congenital hemidysplasia with ichthyosiform nevus and limb defects syndrome, expression of hsp25 (the murine homologue of hsp27) also showed lyonization, demonstrating a clear-cut link between hsp27 expression and underlying molecular pathology. Our results show that loss of hsp27 is a rare event in human epidermis that is associated with specific genetic defects. Among the cases described here, these defects are either in suprabasal keratins or in enzymes involved in cholesterol biosynthesis. The expression and chaperone function of hsp27 might be modified by low/absent epidermal cholesterol and aberrant substrates (ie, keratins) resulting in protein misfolding, dyskeratosis, and thus contribute to the ichthyotic phenotype.

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.

Large congenital melanocytic nevi may reflect paradominant inheritance implying allelic loss.

Large congenital melanocytic nevi have so far always been considered to occur sporadically, and until now little has been written about a possible role of heredity as a cause of this disorder. We reviewed familial cases of large congenital melanocytic nevi as reported in the literature and found 14 case reports with a family history of congenital nevi. We propose the concept of paradominant inheritance as a possible genetic explanation. The concept would imply that heterozygous individuals are phenotypically normal which is why the mutation would be transmitted unperceived through many generations. The trait would become manifest only when loss of heterozygosity occurred at an early developmental stage, giving rise to a patchy area of homozygous or hemizygous cells. This would explain why the lesions of large congenital melanocytic nevi are always arranged in a mosaic pattern; why they occur virtually always sporadically; and why the exceptional cases of a familial aggregation of this trait do not show any consistent Mendelian pattern.

Linear atrophoderma of Moulin: postulation of mosaicism for a predisposing gene.

Hyperpigmented atrophoderma arranged in a pattern following the lines of Blaschko and appearing during childhood or adolescence on the trunk or the limbs is a characteristic feature of linear atrophoderma of Moulin. We review 15 published reports and describe 4 additional cases. Histopathologically, there is no clear sign of atrophy found in specimens examined by light microscopy. It might well be argued that a focal reduction of subcutaneous fatty tissue contributes to the obvious clinical atrophy. The cause and pathogenesis of the disorder remains unknown. It may reflect mosaicism caused by a postzygotic mutation that occurred at an early developmental stage, in analogy to many other diseases distributed along Blaschko's lines. Linear atrophoderma of Moulin may reflect the action of an autosomal lethal gene surviving by mosaicism. There are so far no reports of a familial occurrence that could favor a paradominant transmission of linear atrophoderma of Moulin. However, theoretically, the postzygotic mutation giving rise to an aberrant cell clone could still be nonlethal. In a heterozygous individual, a postzygotic mutational event might lead to loss of the corresponding wild-type allele at the atrophoderma locus. This would give rise to a homozygous cell clone, which becomes manifest along the lines of Blaschko later in life.