Noradrenergic neuronal development is impaired by mutation of the proneural HASH-1 gene in congenital central hypoventilation syndrome (Ondine's curse)

Congenital central hypoventilation syndrome (CCHS, Ondine's curse) is a rare disorder of the chemical control of breathing. It is frequently associated with a broad spectrum of dysautonomic symptoms, suggesting the involvement of genes widely expressed in the autonomic nervous system. In particular, the HASH-1-PHOX2A-PHOX2B developmental cascade was proposed as a candidate pathway because it controls the development of neurons with a definitive or transient noradrenergic phenotype, upstream from the RET receptor tyrosine kinase and tyrosine hydroxylase. We recently showed that PHOX2B is the major CCHS locus, whose mutation accounts for 60% of cases. We also studied the proneural HASH-1 gene and identified a heterozygous nucleotide substitution in three CCHS patients. To analyze the functional consequences of HASH-1 mutations, we developed an in vitro model of noradrenergic differentiation in neuronal progenitors derived from the mouse vagal neural crest, reproducing in vitro the HASH-PHOX-RET pathway. All HASH-1 mutant alleles impaired noradrenergic neuronal development, when overexpressed from adenoviral constructs. Thus, HASH-1 mutations may contribute to the CCHS phenotype in rare cases, consistent with the view that the abnormal chemical control of breathing observed in CCHS patients is due to the impairment of noradrenergic neurons during early steps of brainstem development.     

Testing for BRCA1 mutations: a cost-effectiveness analysis

Breast carcinoma is the most common type of cancer affecting women in the Western world. The hereditary forms, which amount from 5 to 10% of all the cases of breast cancer, mainly involve BRCA1 or BRCA2 mutations. Due to the diagnostic strategy used by the patent owner, Direct DNA sequencing (DS) may become the only BRCA1/2 test procedure available, although there exist several alternative strategies. A cost-effectiveness study was carried out using BRCA1 testing as a model. The main techniques available for performing mutation searches were assessed: DS, denaturing high performance liquid chromatography (DHPLC), single-strand conformation polymorphism (SSCP), denaturing gradient gel electrophoresis (DGGE), heteroduplex analysis (HA), fluorescent assisted mismatch analysis (FAMA) and the protein truncation test (PTT). Twenty strategies involving the use of one or more techniques were then devised for performing the complete genetic analysis. DS was adopted as the 'gold standard' for effectiveness. All the strategies except for DS involved a two-step procedure. The first step consisted of pre-screening the 22 coding exons of BRCA1. The second step consisted of performing DS only on the variations detected in the coding sequence. The cost of the strategies tested, including a pre-screening stage, turned out to be 30 to 90% lower than that of DS, whatever annual use was made of the equipment. The most cost-effective strategy, ie, that corresponding to the lowest cost per mutation detected, was found to be a combination between PTT on exon 11 (60% of the coding sequence) and HA on the remaining 21 exons (PTT(11)+ HA(21)). However, since a high false negative rate is associated with this strategy, at least four other strategies are worth mentioning: PTT(11)+ DHPLC(21), DHPLC alone, FAMA(11)+ DHPLC(21) and FAMA alone. Our results on genetic testing for breast cancer show that DS is not the most cost-effective method available. The monopolist approach of the firm which owns the patents on the BRCA1/2 genes, may, therefore limit the use of the most cost-effective strategies.     

Identification of a novel frameshift mutation in the DFNB31/WHRN gene in a Tunisian consanguineous family with hereditary non-syndromic recessive hearing loss

Approximately 80% of hereditary hearing loss is non-syndromic. Non-syndromic deafness is the most genetically heterogeneous trait. The most common and severe form of hereditary hearing impairment is autosomal recessive non-syndromic hearing loss (ARNSHL), accounting for approximately 80% of cases of genetic deafness. To date, 22 genes implicated in ARNSHL have been identified. Recently a gene, DFNB31/WHRN, which encodes a putative PDZ scaffold protein called whirlin, was found to be responsible for the ARNSHL DFNB31. We found evidence for linkage to the DFNB31locus in a consanguineous Tunisian family segregating congenital profound ARNSHL. Mutation screening of DFNB31/WHRNrevealed four nonpathogenic sequence variants and a novel frameshift mutation [c.2423delG] + [c.2423delG] that changed the reading frame and induced a novel stop codon at amino acid 818 ([p.Gly808AspfsX11] + [p.Gly808AspfsX11]). To determine the contribution of the DFNB31locus in the childhood deafness, we performed linkage analysis in 62 unrelated informative families affected with ARNSHL. No linkage was found to this locus. From this study, we concluded that DFNB31/WHRN is most likely to be a rare cause of ARNSHL in the Tunisian population.     

Clinical evidence of the nonpathogenic nature of the M34T variant in the connexin 26 gene

Mutations in GJB2 are the most common cause of congenital nonsyndromic hearing loss. The controversial allele variant M34T has been hypothesized to cause autosomal dominant or recessive nonsyndromic hearing impairment and some in vitro data has been consistent with this hypothesis. In this report, we present the clinical and genotypic study of 11 families (seven familial forms of nonsyndromic sensorineural hearing loss (NSSNHL) and four sporadic cases) in which the M34T GJB2 variant has been identified. The M34T mutation did not segregate with the deafness in six of the seven familial forms of NSSNH. Eight persons with normal audiogram presented a heterozygous M34T variation and five normal hearing individuals were composite heterozygous for M34T and another GJB2 mutation. Four normal hearing individuals with a documented audiogram were M34T/35delG and one was M34T/(GJB6-D13S1830)del. Screening a French control population of 116 subjects we have found an M34T allele frequency of 1.72%. This percentage was not significatively different from the prevalence of the M34T allele in the deaf population, which was 2.12%. All these data suggest that the M34T variant is not clinically significant in human and is a frequent polymorphism in France.     

Inbreeding Affects Female Preference for Symmetry in Computer-Animated Sticklebacks

Fluctuating asymmetries are small random deviations from perfect symmetry in bilateral traits caused by the inability of individuals to cope with stress during development. The degree of asymmetry of secondary sexual characters is supposed to convey information about a male's phenotypic and/or genetic quality, and females are thus expected to use bilateral symmetry as a cue in mate choice. We offered female three-spined sticklebacks (Gasterosteus aculeatus L.) that had been inbred for one generation and outbred control females the choice between computer-animated male models differing exclusively in the symmetry of their pelvic spines. Inbred females exhibited a significantly stronger preference for the symmetric model than outbred females, suggesting that females of relatively poor quality are more prepared to pay the costs of choosiness and obtain higher marginal benefits from their discrimination than females of better quality.     

Genetic polymorphisms and cerebrospinal fluid levels of tissue inhibitor of metalloproteinases 1 in sporadic Alzheimer's disease

Tissue inhibitor of metalloproteinases 1 (TIMP-1) inhibits several proteinases including a disintegrin and metalloproteinase 10 (ADAM10), a major alpha-secretase that cleaves the beta-amyloid precursor protein within its amyloidogenic Abeta domain. The gene encoding TIMP-1 (TIMP 1) maps to the short arm of the X chromosome, in a region previously suggested as conferring genetic susceptibility for Alzheimer's disease (AD). To determine whether genetic variability of TIMP 1 contributes to the pathogenesis of AD, we analysed one single nucleotide polymorphism within TIMP 1 and one single nucleotide polymorphism in the 5'-untranslated region of TIMP 1 in patients with AD and control subjects from two independent and ethnically different populations. We did not observe any association between TIMP 1 genotypes and the diagnosis of AD in men or women. We also measured TIMP-1 protein levels in the cerebrospinal fluid of patients with AD, healthy control subjects, and patients with other neurological disorders. TIMP-1 levels were similar in all groups. In addition, no significant differences were observed after stratification for TIMP 1 genotypes. Our data show that neither genetic variability nor protein levels of TIMP-1 are associated with AD.     

Matched adaptations of electrophysiological, physiological, and histological properties of skeletal muscles in response to chronic hypoxia

This study tried to differentiate the consequences of chronic hypoxia on the electrophysiological and physiological properties and the histological characteristics of slow and fast muscles in rats. Animals inhaled a 10% O₂ concentration for a 1-month period. Then, slow [soleus (SOL)] and fast [extensor digitorum longus (EDL)] muscles were analyzed in vitro by physiological and electrophysiological measurements and histological analyses. The results were compared to those obtained in corresponding muscles of an age-matched normoxic group. After exposure to hypoxia: (1) in SOL, there was a tendency to elevated F_max, a significant increase in twitch force and tetanic frequency and a shortening of M-wave duration, and a reduced percentage of type I fibres, whereas the proportion of type IIa fibres doubled; (2) in EDL, F_max and tetanic frequency were lowered, the muscle became less resistant to fatigue, and the proportion of type IId/x fibres was halved. Then, after 1 month of hypoxia, in the SOL muscle, both the contractile and histological properties resemble those of a fast muscle. By contrast, the EDL became slower, despite its histology was modestly affected. Reduced muscle use in hypoxia could explain the tendency for deteriorating adaptations in EDL, and the faster properties of SOL could result from hypoxia-induced inhibition of the growth-related fast-to-slow shift in muscle fibre types.