Identification of a novel in-frame deletion in KCNQ4 (DFNA2A) and evidence of multiple phenocopies of unknown origin in a family with ADSNHL.

Autosomal dominant sensorineural hearing loss (ADSNHL) is extremely genetically heterogeneous, making it difficult to molecularly diagnose. We identified a multiplex (n=28 affected) family from the genetic isolate of Newfoundland, Canada with variable SNHL and used a targeted sequencing approach based on population-specific alleles in WFS1, TMPRSS3 and PCDH15; recurrent mutations in GJB2 and GJB6; and frequently mutated exons of KCNQ4, COCH and TECTA. We identified a novel, in-frame deletion (c.806_808delCCT: p.S269del) in the voltage-gated potassium channel KCNQ4 (DFNA2), which in silico modeling predicts to disrupt multimerization of KCNQ4 subunits. Surprisingly, 10/23 deaf relatives are non-carriers of p.S269del. Further molecular characterization of the DFNA2 locus in deletion carriers ruled out the possibility of a pathogenic mutation other than p.S269del at the DFNA2A/B locus and linkage analysis showed significant linkage to DFNA2 (maximum LOD=3.3). Further support of genetic heterogeneity in family 2071 was revealed by comparisons of audio profiles between p.S269del carriers and non-carriers suggesting additional and as yet unknown etiologies. We discuss the serious implications that genetic heterogeneity, in this case observed within a single family, has on molecular diagnostics and genetic counseling.

High incidence of pediatric idiopathic epilepsy is associated with familial and autosomal dominant disease in Eastern Newfoundland.

PURPOSE: To describe the incidence and epidemiology of pediatric idiopathic epilepsy (IE) in Newfoundland and Labrador. METHODS: All children in Newfoundland and Labrador aged 0-15 years with IE were ascertained through the provincial neurology clinic at the Janeway Child Health Centre. Family history, medical history and blood samples were obtained from probands and relatives. Two genes, SCN1A and KCNQ2, were screened for mutations by direct sequencing. RESULTS: The mean annual incidence of IE for the population of children living in the Avalon region of Newfoundland from 2000 to 2004 was 107 per 100,000. This rate is approximately three-fold greater than rates reported in other developed countries. Of 117 families with IE eligible for study, 86 (74%) provided detailed pedigree data. Multiple different epilepsy phenotypes were identified. Fifty-five families (64%) had a positive family history. Eight of these had family histories compatible with autosomal dominant (AD) inheritance and these families lived in five different geographic isolates. DNA was obtained from 21 families (79 individuals). The two previously identified mutations in Newfoundland families with epilepsy were sequenced and excluded as pathogenic sites in all but one family which had a mutation in SCN1A. CONCLUSION: The incidence of IE is high in the Avalon Peninsula of Newfoundland and the rate of familial disease is high throughout the province of Newfoundland and Labrador. The distribution of familial and AD IE in different geographic isolates, together with the clinical heterogeneity of disease suggests substantial genetic heterogeneity. It is likely that other novel mutations will be identified in this population.

C/EBPalpha and beta couple interfollicular keratinocyte proliferation arrest to commitment and terminal differentiation.

The transcriptional regulators that couple interfollicular basal keratinocyte proliferation arrest to commitment and differentiation are yet to be identified. Here we report that the basic region leucine zipper transcription factors C/EBPalpha and C/EBPbeta are co-expressed in basal keratinocytes, and are coordinately upregulated as keratinocytes exit the basal layer and undergo terminal differentiation. Mice lacking both C/EBPalpha and beta in the epidermis showed increased proliferation of basal keratinocytes and impaired commitment to differentiation. This led to ectopic expression of keratin 14 (K14) and DeltaNp63 in suprabasal cells, decreased expression of spinous and granular layer proteins, parakeratosis and defective epidermal water barrier function. Knock-in mutagenesis revealed that C/EBP-E2F interaction was required for control of interfollicular epidermis (IFE) keratinocyte proliferation, but not for induction of spinous and granular layer markers, whereas C/EBP DNA binding was required for DeltaNp63 downregulation and K1/K10 induction. Finally, loss of C/EBPalpha/beta induced stem cell gene expression signatures in the epidermis. C/EBPs, therefore, couple basal keratinocyte cell cycle exit to commitment to differentiation through E2F repression and DNA binding, respectively, and may act to restrict the epidermal stem cell compartment.

Variable neurologic phenotype in a GEFS+ family with a novel mutation in SCN1A.

PURPOSE: To describe the spectrum of clinical disease in a mutliplex family with an autosomal dominant form of generalized epilepsy with febrile seizures plus (GEFS+) and determine its genetic etiology. METHODS: Medical and family history was obtained on 11 clinically affected individuals and their relatives across three generations through medical chart review and home visits. A candidate gene approach including haplotype analysis and direct sequencing was used. RESULTS: An epilepsy-associated haplotype was identified on 2q24. Direct sequencing of the entire SCN1A gene identified seven sequence variants. However, only one of these, c.1162 T>C, was not found in population controls. This transition in exon 8 of SCN1A predicts a substitution (Y388H) of a highly conserved tyrosine residue in the loop between transmembrane segments S5 and S6 of the sodium channel protein (Na(v)1.1). Clinical features in mutation carriers of this novel missense mutation were highly variable, ranging from febrile seizures to severe refractory epilepsy. CONCLUSION: A novel missense mutation in the pore-forming region of the sodium channel gene SCN1A causes GEFS+ with a variable phenotype that includes mood and anxiety disorders, as well as ataxia, expanding the GEFS+ spectrum to include neuropsychiatric disease.

Autosomal recessive Bardet-Biedl syndrome: first-degree relatives have no predisposition to metabolic and renal disorders.

Bardet-Biedl Syndrome (BBS) is an autosomal recessive, multisystem, genetically heterogeneous, ciliopathic condition caused by mutations in multiple genes. Here we sought to determine if inheritance of a single BBS mutation increased the risks of frequent disorders of this syndrome such as obesity, hypertension, and diabetes. Various metabolic and renal diseases in a cohort of 46 patients with BBS, prospectively followed for up to 28 years, were compared to recent assessments of these factors in 96 relatives with a heterozygote mutation (carriers) and 37 relatives without a contributing mutation (non-carriers). Ten mutations in 6 genes causing this syndrome were identified in 21 families from whom DNA was obtained. The body mass index or the incidences of hypertension, diabetes, or stage 3 chronic kidney diseases were found to be similar between carriers and non-carriers but were all significantly less than those of family members with BBS. Similarly, the median age of onset of hypertension or diagnosis of stage 3 kidney disease, or the diagnosis of diabetes by age 70 were all significantly lower in those with BBS than in gene carriers or non-carriers. While our study shows that metabolic and renal events occurred frequently and at an early age in BBS, the heterozygous inheritance of any of the 10 described BBS mutations did not predispose family members to obesity, diabetes, hypertension, or renal impairment.

Clinical and genetic epidemiology of Bardet-Biedl syndrome in Newfoundland: a 22-year prospective, population-based, cohort study.

Bardet-Biedl syndrome (BBS) and Laurence-Moon syndrome (LMS) have a similar phenotype, which includes retinal dystrophy, obesity, and hypogenitalism. They are differentiated by the presence of spasticity and the absence of polydactyly in LMS. The aims of this study were to describe the epidemiology of BBS and LMS, further define the phenotype, and examine genotype-phenotype correlation. The study involved 46 patients (26 males, 20 females) from 26 families, with a median age of 44 years (range 1-68 years). Assessments were performed in 1986, 1993, and 2001 and included neurological assessments, anthropometric measurements, and clinical photographs to assess dysmorphic features. The phenotype was highly variable within and between families. Impaired co-ordination and ataxia occurred in 86% (18/21). Thirty percent (14/46) met criteria for psychiatric illness; other medical problems included cholecystectomy in 37% (17/46) and asthma in 28% (13/46). Dysmorphic features included brachycephaly, large ears, and short, narrow palpebral fissures. There was no apparent correlation of clinical or dysmorphic features with genotype. Two patients were diagnosed clinically as LMS but both had mutations in a BBS gene. The features in this population do not support the notion that BBS and LMS are distinct. The lack of a genotype-phenotype correlation implies that BBS proteins interact and are necessary for the development of many organs.

Mutations in a member of the Ras superfamily of small GTP-binding proteins causes Bardet-Biedl syndrome.

RAB, ADP-ribosylation factors (ARFs) and ARF-like (ARL) proteins belong to the Ras superfamily of small GTP-binding proteins and are essential for various membrane-associated intracellular trafficking processes. None of the approximately 50 known members of this family are linked to human disease. Using a bioinformatic screen for ciliary genes in combination with mutational analyses, we identified ARL6 as the gene underlying Bardet-Biedl syndrome type 3, a multisystemic disorder characterized by obesity, blindness, polydactyly, renal abnormalities and cognitive impairment. We uncovered four different homozygous substitutions in ARL6 in four unrelated families affected with Bardet-Biedl syndrome, two of which disrupt a threonine residue important for GTP binding and function of several related small GTP-binding proteins. Analysis of the Caenorhabditis elegans ARL6 homolog indicates that it is specifically expressed in ciliated cells, and that, in addition to the postulated cytoplasmic functions of ARL proteins, it undergoes intraflagellar transport. These findings implicate a small GTP-binding protein in ciliary transport and the pathogenesis of a pleiotropic disorder.

NKIAMRE, a novel conserved CDC2-related kinase with features of both mitogen-activated protein kinases and cyclin-dependent kinases.

We report the cloning of the NKIAMRE gene located on human chromosome 5q31.1. It encodes a novel 52kDa Cdc2-related kinase with a 1.5kb open reading frame. Like MAP kinases, NKIAMRE contains a Thr-X-Tyr (TXY) motif in the activation loop domain. Similar to cdks, NKIAMRE contains the putative negative regulatory Ser14 and Tyr15 residues and the cyclin-binding motif, NKIAMRE, from which it derives its name. Human NKIAMRE has significant amino acid identity to related kinases in rat, mouse, Caenorhabditis elegans, and Drosophila, and is widely expressed in human tissues and cell lines. Confocal microscopy demonstrates that NKIAMRE localizes to the cytoplasm. NKIAMRE is activated by treatment of cells with phorbol 12-myristate 13-acetate. Mutation of the ATP-binding Lys-33 to arginine and the Thr-Glu-Tyr motif to Ala-Glu-Phe abolished its ability to phosphorylate myelin basic protein. NKIAMRE is a member of a conserved family of kinases with homology to both MAP kinases and cyclin-dependent kinases.

Ophthalmic findings in fetal anticonvulsant syndrome(s).

PURPOSE: To report the prevalence of ocular abnormalities in a group of children diagnosed with fetal anticonvulsant (FAC) syndrome(s). DESIGN: Retrospective, observational, noncomparative case series. PARTICIPANTS: Forty-six children, age range 8 months to 16 years 5 months (mean, 7 years 1 month), with a confirmed diagnosis of an FAC syndrome. Thirty-seven subjects were exposed in utero to sodium valproate (29 as monotherapy), and the remainder (n = 9) to other anticonvulsants, mainly carbamazepine. METHODS: A total of 46 subjects underwent ophthalmic assessment consisting of visual acuity, cover test, ocular movements, analysis of spectacle lens power, cycloplegic refraction, and anterior segment examination with portable slit lamp, plus direct and indirect ophthalmoscopy. MAIN OUTCOME MEASURES: Refraction and ocular motility status. RESULTS: Thirty-one of 46 (67%) had ocular abnormalities, most commonly errors of refraction (19 of 46; 41%). Myopia was common (14 of 28; 50%) in those exposed to valproate monotherapy and there were high frequencies of strabismus (20%), astigmatism (24%), and anisometropia (11%) in the group as a whole. Thirty-one percent of myopes and 27% of astigmates did not wear glasses, of whom three subjects and two subjects, respectively, were less than 8 years old and therefore at risk of anisometropic or ametropic amblyopia. One subject had epicanthus, one color vision deficiency, and one bilateral congenital cataract. CONCLUSIONS: We conclude that (1) abnormal ophthalmic findings are common in subjects with confirmed FAC syndrome, in particular myopia in those with fetal valproate syndrome; (2) children with FAC syndrome should receive preschool vision testing; (3) preschool vision testing should be considered in all children exposed to anticonvulsants in utero.