A novel missense mutation of NSDHL in an unusual case of CHILD syndrome showing bilateral, almost symmetric involvement

The CHILD syndrome (MIM 308050), an acronym for congenital hemidysplasia with ichthyosiform nevus and limb defects, is an X-linked dominant trait with lethality for male embryos. Recently, we elucidated the underlying gene defect by demonstrating point mutations in NSDHL (NAD[P]H steroid dehydrogenase-like protein) at Xq28 in 6 patients with classic CHILD syndrome. The most striking clinical feature is an inflammatory nevus that usually shows a unique lateralization with strict midline demarcation. Ipsilateral defects involve all skeletal structures and internal organs such as the brain, the lung, the heart, or the kidney. As an exception to this rule, in some cases the CHILD nevus may occur in a more or less bilateral distribution. In 1997 Fink-Puches et al described a case of CHILD nevus with an almost symmetric arrangement. To test the correctness of the diagnosis, we now examined blood lymphocytes of this patient by single-strand conformation analysis and genomic sequencing. We identified a novel missense mutation in NSDHL that potentially may impair protein function. We conclude that a diagnosis of CHILD syndrome can be based on clinical features such as the highly characteristic morphology of the CHILD nevus. A symmetric distribution of this nevus can exceptionally be seen in patients with CHILD syndrome, and this bilateral involvement should not mislead the clinician to any other diagnosis. Apparently, the effect of random X-inactivation is responsible for different patterns of cutaneous involvement in female carriers of NSDHL mutations. (J Am Acad Dermatol 2002;46:594-6.

Keratosis Follicularis Spinulosa Decalvans Is Caused by Mutations in MBTPS2

Keratosis Follicularis Spinulosa Decalvans (KFSD) is a rare genetic disorder characterized by development of hyperkeratotic follicular papules on the scalp followed by progressive alopecia of the scalp, eyelashes, and eyebrows. Associated eye findings include photophobia in childhood and corneal dystrophy. Due to the genetic and clinical heterogeneity of similar disorders, a definitive diagnosis of KFSD is often challenging. Toward identification of the causative gene we reanalyzed a large Dutch KFSD family. SNP arrays (1 M) redefined the locus to a 2.9-Mb region at Xp22.12-Xp22.11. Screening of all 14 genes in the candidate region identified MBTPS2 as the candidate gene carrying a c.1523A>G (p.Asn508Ser) missense mutation. The variant was also identified in two unrelated X-linked KFSD families and cosegregated with KFSD in all families. In symptomatic female carriers, skewed X-inactivation of the normal allele matched with increased severity of symptoms. MBTPS2 is required for cleavage of sterol regulatory element-binding proteins (SREBPs). In vitro functional expression studies of the c. 1523A>G mutation showed that sterol responsiveness was reduced by half. Other missense mutations in MBTPS2 have recently been identified in patients with IFAP syndrome. We postulate that both phenotypes are in the spectrum of one genetic disorder with a partially overlapping phenotype. Hum Mutat 31:1125-1133, 2010. (C) 2010 Wiley-Liss, Inc

Point Mutations Throughout the GLI3 Gene Cause Greig Cephalopolysyndactyly Syndrome

Greig cephalopolysyndactyly syndrome, characterized by craniofacial and limb anomalies (GCPS; MIM 175700), previously has been demonstrated to be associated with translocations as well as point mutations affecting one allele of the zinc finger gene GLI3. In addition to GCPS, Pallister-Hall syndrome (PHS; MIM 146510) and post-axial polydactyly type A (PAP-A; MIM 174200), two other disorders of human development, are caused by GLI3 mutations. In order to gain more insight into the mutational spectrum associated with a single phenotype, we report here the extension of the GLI3 mutation analysis to 24 new GCPS cases. We report the identification of 15 novel mutations present in one of the patient's GLI3 alleles. The mutations map throughout the coding gene regions. The majority are truncating mutations (nine of 15) that engender prematurely terminated protein products mostly but not exclusively N-terminally to or within the central region encoding the DNA-binding domain. Two missense and two splicing mutations mapping within the zinc finger motifs presumably also interfere with DNA binding. The five mutations identified within the protein regions C-terminal to the zinc fingers putatively affect additional functional properties of GLI3. In cell transfection experiments using fusions of the DNA-binding domain of yeast GAL4 to different segments of GLI3, transactivating capacity was assigned to two adjacent independent domains (TA1 and TA2) in the C-terminal third of GLI3. Since these are the only functional domains affected by three C-terminally truncating mutations, we postulate that GCPS may be due either to haploinsufficiency resulting from the complete loss of one gene copy or to functional haploinsufficiency related to compromised properties of this transcription factor such as DNA binding and transactivatio

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

Mutations Affecting The Bhlha9 Dna-Binding Domain Cause Mssd, Mesoaxial Synostotic Syndactyly With Phalangeal Reduction, Malik-Percin Type

Mesoaxial synostotic syndactyly, Malik-Percin type (MSSD) (syndactyly type IX) is a rare autosomal-recessive nonsyndromic digit anomaly with only two affected families reported so far. We previously showed that the trait is genetically distinct from other syndactyly types, and through autozygosity mapping we had identified a locus on chromosome 17p13.3 for this unique limb malformation. Here, we extend the number of independent pedigrees from various geographic regions segregating MSSD to a total of six. We demonstrate that three neighboring missense mutations affecting the highly conserved DNA-binding region of the basic helix-loop-helix A9 transcription factor (BHLHA9) are associated with this phenotype. Recombinant BHLHA9 generated by transient gene expression is shown to be located in the cytoplasm and the cell nucleus. Transcription factors 3, 4, and 12, members of the E protein (class I) family of helix-loop-helix transcription factors, are highlighted in yeast two-hybrid analysis as potential dimerization partners for BHLHA9. In the presence of BHLHA9, the potential of these three proteins to activate expression of an E-box-regulated target gene is reduced considerably. BHLHA9 harboring one of the three substitutions detected in MSSD-affected individuals eliminates entirely the transcription activation by these class I bHLH proteins. We conclude that by dimerizing with other bHLH protein monomers, BHLHA9 could fine tune the expression of regulatory factors governing determination of central limb mesenchyme cells, a function made impossible by altering critical amino acids in the DNA binding domain. These findings identify BHLHA9 as an essential player in the regulatory network governing limb morphogenesis in humans.WoSScopu

Mutations in SREBF1, Encoding Sterol Regulatory Element Binding Transcription Factor 1, Cause Autosomal-Dominant IFAP Syndrome

IFAP syndrome is a rare genetic disorder characterized by ichthyosis follicularis, atrichia, and photophobia. Previous research found that mutations in MBTPS2, encoding site-2-protease (S2P), underlie X-linked IFAP syndrome. The present report describes the identification via whole-exome sequencing of three heterozygous mutations in SREBF1 in 11 unrelated, ethnically diverse individuals with autosomal-dominant IFAP syndrome. SREBF1 encodes sterol regulatory element-binding protein 1 (SREBP1), which promotes the transcription of lipogenes involved in the biosynthesis of fatty acids and cholesterols. This process requires cleavage of SREBP1 by site-1-protease (S1P) and S2P and subsequent translocation into the nucleus where it binds to sterol regulatory elements (SRE). The three detected SREBF1 mutations caused substitution or deletion of residues 527, 528, and 530, which are crucial for S1P cleavage. In vitro investigation of SREBP1 variants demonstrated impaired S1P cleavage, which prohibited nuclear translocation of the transcriptionally active form of SREBP1. As a result, SREBP1 variants exhibited significantly lower transcriptional activity compared to the wild-type, as demonstrated via luciferase reporter assay. RNA sequencing of the scalp skin from IFAP-affected individuals revealed a dramatic reduction in transcript levels of low-density lipoprotein receptor (LDLR) and of keratin genes known to be expressed in the outer root sheath of hair follicles. An increased rate of in situ keratinocyte apoptosis, which might contribute to skin hyperkeratosis and hypotrichosis, was also detected in scalp samples from affected individuals. Together with previous research, the present findings suggest that SREBP signaling plays an essential role in epidermal differentiation, skin barrier formation, hair growth, and eye function

First genome-wide association study of esophageal atresia identifies three genetic risk loci at CTNNA3, FOXF1/FOXC2/FOXL1, and HNF1B

Esophageal atresia with or without tracheoesophageal fistula (EA/TEF) is the most common congenital malformation of the upper digestive tract. This study represents the first genome-wide association study (GWAS) to identify risk loci for EA/TEF. We used a European case-control sample comprising 764 EA/TEF patients and 5,778 controls and observed genome-wide significant associations at three loci. On chromosome 10q21 within the gene CTNNA3 (p = 2.11 x 10(-8); odds ratio [OR] = 3.94; 95% confidence interval [CI], 3.10-5.00), on chromosome 16q24 next to the FOX gene cluster (p = 2.25 x 10(-10); OR = 1.47; 95% CI, 1.38-1.55) and on chromosome 17q12 next to the gene HNF1B (p = 3.35 x 10(-16); OR = 1.75; 95% CI, 1.64-1.87). We next carried out an esophageal/tracheal transcriptome profiling in rat embryos at four selected embryonic time points. Based on these data and on already published data, the implicated genes at all three GWAS loci are promising candidates for EA/TEF development. We also analyzed the genetic EA/TEF architecture beyond the single marker level, which revealed an estimated single-nucleotide polymorphism (SNP)-based heritability of around 37% +/- 14% standard deviation. In addition, we examined the polygenicity of EA/TEF and found that EA/TEF is less polygenic than other complex genetic diseases. In conclusion, the results of our study contribute to a better understanding on the underlying genetic architecture of ET/TEF with the identification of three risk loci and candidate genes