Arne König

Mutations in the NSDHL gene, encoding a 3β-hydroxysteroid dehydrogenase, cause CHILD syndrome

We report for the first time that CHILD syndrome (MIM 308050), an X-linked dominant, male-lethal trait characterized by an inflammatory nevus with striking lateralization and strict midline demarcation, as well as ipsilateral hypoplasia of the body is caused by mutations in the gene NSDHL located at Xq28 (NAD(P)H steroid dehydrogenase-like protein) encoding a 3beta-hydroxysteroid dehydrogenase functioning in the cholesterol biosynthetic pathway. SSCA and genomic sequence analysis of NSDHL identified in 6 patients with CHILD syndrome, including one boy as well as a mother and her daughter, mutations potentially impairing protein function. This phenotype is distinct from, but shares various clinical and biochemical findings with chondrodysplasia punctata (CDPX2, MIM 302960). CDPX2 is due to mutations affecting a delta8-delta7 sterol isomerase (EBP, emopamil binding protein, at Xp11.22-p11.23) that functions downstream of NSDHL in a later step of cholesterol biosynthesis. EBP was unaffected in the patients analyzed by us demonstrating that CHILD syndrome and CDPX2 are not caused by allelic mutations. Two mouse X-linked dominant male-lethal traits, bare patches (Bpa) and striated (Str) had previously been associated with mutations in Nsdhl. They provide animal models for the study of CHILD syndrome, a further human condition due to mutations in a gene of the cholesterol synthesis pathway.

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.

Cigarette smoking as a triggering factor of Hidradenitis suppurativa

Background: Hidradenitis suppurativa is a chronic inflammatory skin disease involving the axillary, inguinal and anogenital regions and sometimes, in addition, the submammary or sacral areas. The etiology of this condition is unknown. Objective: A matched-pair case-control study was performed to evaluate the influence of smoking habits on the manifestation of this disease. Methods: Patients who had received surgical treatment for hidradenitis suppurativa in two dermatological centers completed a questionnaire dealing with family history, course of the disease and smoking habits. To form a randomized matched-pair control group, an equal number of patients admitted for various other skin diseases such as atopic dermatitis, varicose veins, skin tattoos, alopecia areata or melanoma was matched for sex and age and evaluated for smoking habits. Statistical analysis was performed by use of several χ2 tests in a cross-table setting. Moreover, a comparison to the expected smoking prevalence in Germany based on national statistics was performed. Results: Out of 84 patients treated for hidradenitis suppurativa, 63 subjects (27 men, 36 women) completed the questionnaire. The rate of active cigarette smokers was 88.9% (56 patients), whereas 4 subjects (6.4%) had never smoked. 3 patients (4.8%) stated to be ex-smokers, but 2 of these had quit smoking only recently and after onset of the disease. The rate of smokers in the matched-pair control group was 46%. The significantly higher proportion of active smokers among patients with hidradenitis suppurativa can be expressed by an odds ratio of 9.4, the calculated 95% confidence interval was 3.7–23.7 (p < 0.001). The expected smoking prevalence in Germany was 26.7% according to national statistics. 73% of our patients had no family history of hidradenitis suppurativa whereas 27% reported at least one affected first-degree relative. Conclusion: From the exceedingly high rate of smokers among patients with this condition we conclude that cigarette smoking is a major triggering factor of hidradenitis suppurativa. Remarkably, the disease can be categorized as a smoking sequel that is neither of vascular nor neoplastic nature. Because familial occurrence was rather rarely reported, and because an environmental factor in the form of cigarette smoking appears to be of crucial importance to trigger the disease, we assume that the genetic basis of hidradenitis suppurativa is polygenic rather than mendelian. Smoking cessation should be encouraged particularly in patients with hidradenitis suppurativa although it is unknown whether this improves the course of the disease.

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.

HID and KID syndromes are associated with the same connexin 26 mutation

Summary Background Keratitis–ichthyosis–deafness (KID) syndrome is a debilitating ectodermal dysplasia that predisposes patients to develop squamous cell carcinomas in addition to leading to profound sensory deafness and erythrokeratoderma. We recently demonstrated that KID can be caused by a specific missense mutation in connexin 26 (GJB2). Another syndrome, called hystrix‐like ichthyosis–deafnesss (HID) syndrome, strongly resembles the KID syndrome. These disorders are distinguished mainly on the basis of electron microscopic findings. We hypothesized that KID and HID syndromes may be genetically related.

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.

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.

Mutational spectrum of NSDHL in CHILD syndrome

CHILD syndrome (congenital hemidysplasia with ichthyosiform nevus and limb defects, MIM 308050) is an X linked dominant, male lethal, multisystem birth defect characterised by an inflammatory epidermal nevus showing a unique lateralisation pattern and strict midline demarcation. Hypoplasia or aplasia of skeletal or visceral structures may be found ipsilateral to the major cutaneous involvement.1 Owing to the highly characteristic clinical and histopathological features of the CHILD naevus,2 a diagnosis can be established not only in classical cases (fig 1) but also in cases with minimal or atypical involvement.3 In 2000, mutations in NSDHL (NAD(P)H steroid dehydrogenase-like protein) at Xq28 were identified by some of us to be the cause of this syndrome.4 Four additional NSDHL mutations have subsequently been reported in individuals with CHILD syndrome.5–8 Studies carried out on the murine Nsdhl mutants bare patches (Bpa) and striated (Str) have shown that this gene encodes a 3β-hydroxysteroid dehydrogenase (3β-HSD) that catalyses a step in the post-squalene cholesterol biosynthetic pathway and is localised within membranes of the endoplasmic reticulum and on the surface of intracellular lipid storage droplets.9–11 Non-functional NSDHL might cause the CHILD phenotype through a lack of cholesterol or other sterols downstream of the block in biosynthesis, or by the accumulation of intermediates upstream of the product generated by NSDHL. Figure 1  Thirteen year old patient with CHILD syndrome (case 9, table 1): ichthyosiform nevus showing lateralisation with unilateral distribution and midline demarcation; ipsilateral hypoplasia of arm and hand. Reproduced with permission. A related trait, X linked dominant chondrodysplasia punctata (CDPX2, MIM 302960),22 is caused by mutations in EBP (emopamil binding protein) at Xp11.22–p11.23 that functions similarly in the late cholesterol biosynthesis, downstream of NSDHL .23,24 In the past, a case of X linked dominant chondrodysplasia punctata showing unilateral involvement …

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.

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 Blaschkos 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.