Dominant negative effects of SCN5A missense variants

PurposeUp to 30% of patients with Brugada syndrome (BrS) carry loss-of-function (LoF) variants in the cardiac sodium channel gene SCN5A encoding for the protein Na_V1.5. Recent studies suggested that Na_V1.5 can dimerize, and some variants exert dominant negative effects. In this study, we sought to explore the generality of missense variant Na_V1.5 dominant negative effects and their clinical severity.MethodsWe identified 35 LoF variants (<10% of wild type [WT] peak current) and 15 partial LoF variants (10%-50% of WT peak current) that we assessed for dominant negative effects. SCN5A variants were studied in HEK293T cells, alone or in heterozygous coexpression with WT SCN5A using automated patch clamp. To assess the clinical risk, we compared the prevalence of dominant negative vs putative haploinsufficient (frameshift, splice, or nonsense) variants in a BrS consortium and the Genome Aggregation Database population database.ResultsIn heterozygous expression with WT, 32 of 35 LoF and 6 of 15 partial LoF variants showed reduction to <75% of WT-alone peak current, showing a dominant negative effect. Individuals with dominant negative LoF variants had an elevated disease burden compared with the individuals with putative haploinsufficient variants (2.7-fold enrichment in BrS cases, P = .019).ConclusionMost SCN5A missense LoF variants exert a dominant negative effect. This class of variant confers an especially high burden of BrS.     

Clinical evaluation and etiologic diagnosis of hearing loss: A clinical practice resource of the American College of Medical Genetics and Genomics (ACMG)

Hearing loss is a common and complex condition that can occur at any age, can be inherited or acquired, and is associated with a remarkably wide array of etiologies. The diverse causes of hearing loss, combined with the highly variable and often overlapping presentations of different forms of hearing loss, challenge the ability of traditional clinical evaluations to arrive at an etiologic diagnosis for many deaf and hard-of-hearing individuals. However, identifying the etiology of hearing loss may affect clinical management, improve prognostic accuracy, and refine genetic counseling and assessment of the likelihood of recurrence for relatives of deaf and hard-of-hearing individuals. Linguistic and cultural identities associated with being deaf or hard-of-hearing can complicate access to and the effectiveness of clinical care. These concerns can be minimized when genetic and other health care services are provided in a linguistically and culturally sensitive manner. This clinical practice resource offers information about the frequency, causes, and presentations of hearing loss and suggests approaches to the clinical and genetic evaluation of deaf and hard-of-hearing individuals aimed at identifying an etiologic diagnosis and providing informative and effective patient education and genetic counseling.     

Metabolic and Genetic Risk Factors Are the Strongest Predictors of Severity of Alcohol-Related Liver Fibrosis

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Association between a restriction fragment length polymorphism at the liver/islet cell (GluT 2) glucose transporter and familial Type 2 (non-insulin-dependent) diabetes mellitus

Summary Patients with Type 2 (non-insulin-dependent) diabetes mellitus and a strong family history of the disease may represent a sub-group where genetic factors play a pree-minent role in transmission of the disease. A defect in the liver/islet cell glucose transporter (GluT 2) could explain many of the pathophysiological features of the disease. In order to test the hypothesis that genetic variation at the GluT 2 locus contributes genetic susceptibility to Type 2 diabetes, 60 unrelated Caucasian diabetic patients with at least one affected sibling were genotyped for a Taq 1 restriction fragment length polymorphism marker. Hybridisation with a cDNA GluT 2 probe identified two alleles of sizes 13 kilobase (T1) and 19 kilobase (T2). The allele frequencies in the diabetic group with a family history were significantly different from those in a racially-matched control population of 122 subjects with no personal or family history of the disease (diabetic patients T1=0.96, T2=0.04, control subjects T1=0.89, T2=0.11, p< 0.03). However, when the study was repeated with 54 diabetic patients with indeterminate family history, statistical significance was not reached although the allele frequencies showed a similar trend. The findings of this study support the hypothesis that a genetic variant of the liver/islet cell glucose transporter may contribute to familial susceptibility in Type 2 diabetes.R. D. Lawrence Fellow of the British Diabetic Association     

Uptake and metabolism of free cyanocobalamin by cultured human fibroblasts from controls and a patient with transcobalamin II deficiency

We have investigated the uptake and metabolism of free cyanocobalamin (CN-Cbl; vitamin B₁₂) by intact cultured human skin fibroblasts. Monolayers of control fibroblasts take up free CN-[⁵⁷Co]Cbl via a saturable, calcium-independent process that is inhibited by sulfhydryl reagents, inhibitors of protein synthesis, and inhibitors of electron transport, but not by inhibitors of glycolysis. CN-Cbl taken up in this manner is converted to active cobalamin (Cbl) coenzymes (adenosylcobalamin and methylcobalamin) and becomes associated with intracellular Cbl-dependent apoenzymes (methylmalonyl CoA mutase and homocysteine:methyltetrahydrofolate methyltransferase). Since fibroblasts from controls were also found to synthesize transcobalamin II (TC II), a plasma protein shown previously to facilitate the cellular uptake of Cbl, it seemed possible that the observed uptake of free CN-Cbl was TC II-mediated. This thesis was rejected by demonstrating that cells from a patient with complete TC II deficiency took up free CN-Cbl as well as control cells did. Finally, we propose a mechanism by which an uptake process for free Cbl might serve a function in intracellular metabolism of Cbl.     

Association analysis of Arg16Gly polymorphism of the beta2-adrenergic receptor gene in offspring from hypertensive and normotensive families

Objective: Since β2 -adrenergic receptors ( β2 AR) can influence blood pressure not only by vasodilation, but also participate in noradrenaline release from sympathetic nerve endings, we have studied whether Arg16Gly polymorphism of the β2 AR gene is associated with predisposition to essential hypertension and increased plasma noradrenaline concentration in offspring from normotensive (SN) and hypertensive parents (SH). Design and methods: The study population consisted of 105 young SN and 101 SH subjects matched for age and body mass index. Arg16Gly polymorphism of the β2 AR gene was determined by polymerase chain reaction (PCR) technique and subsequent incubation with NcoI restriction enzyme. Resulting fragments were separated using electrophoresis on a 4.2% Metaphor agarose gel. Results: SH already had significantly higher systolic BP, and a tendency to higher diastolic BP than the SN group. The frequency of Arg/Arg homozygotes was significantly increased in SH when compared to SN (25% vs 15%). Results of logistic regression analysis showed the highest relative risk for the Arg/Arg genotype and suggested a recessive action of the Arg16 variant. There was an increased diastolic BP in Arg/Arg homozygotes of the SN group ( p = 0.029). This genotype also had a tendency to increased heart rate in both groups ( p = 0.049). There was no relationship of this polymorphism with plasma noradrenaline concentration. Conclusion: Our findings suggest that genetic variability of the β2 AR gene is implicated in predisposition to essential hypertension. However, the contradictory results between individual studies indicate that the action of the β2 AR gene is indirect, through multiple intermediate phenotypes and gene interactions.     

有遗传史的原发性高血压患者子代血浆内皮素和一氧化氮浓度的比较性研究

目的 :探讨内皮素 1(ET 1)与一氧化氮 (NO)在有遗传史的原发性高血压 (EH)子代中的作用及临床意义。方法 :用ELISA方法检测有EH遗传史的患者及其子代和正常人群者及其子代血浆ET 1和NO水平 ,并将两者进行比较。结果 :①EH患者比正常人群者血浆ET 1水平明显升高 (P <0 .0 1) ,血浆NO水平也明显高于后者 (P <0 .0 1)。②有EH遗传史的血压正常的子代与正常人群的子代相比 ,血浆ET 1水平差异无显著性意义 (P >0 .0 5 ) ,而前者NO水平明显高于后者 ,差异有非常显著性意义 (P <0 .0 1)。结论 :①EH患者血浆ET 1水平明显升高 ,而在他们血压正常的子代中不增高。提示 :EH可引起机体内血浆ET 1水平增高 ,从而参与或促进EH的发展 ;但这种高ET 1水平 ,可能并无遗传性。②有EH家族史血压正常的子代中 ,血浆NO水平增高 ,提示在这些人的机体内 ,可能存在NO抵抗作用。     

Association of Alcohol or Other Drug Dependence with Alleles of the μ Opioid Receptor Gene (OPRM1)

Opioidergic neurotransmission and, specifically, the μ opioid receptor have been implicated in the reinforcing effects of a variety of drugs of abuse. Consequently, the present study examined the association of a polymorphic (CA)n repeat at the OPRM1 locus (the gene coding for the μ opioid receptor) to alcohol or drug dependence in 320 Caucasian and 108 African-American substance-dependent or control subjects. Among Caucasians, suggestion of a modest association, which could be interpreted as statistically significant ( p = 0.03), was observed between OPRMl alleles and substance (alcohol, cocaine, or opioid) dependence. Analysis by specific substance showed only a trend level association to alcohol dependence. Comparisons among African Americans yielded no evidence for association. Further studies of the association between alleles of the OPRM1 gene and substance dependence appear warranted, particularly if they use a family-based approach to control for population stratication. Phenotypes other than a broad diagnostic categorization, such as opioid antagonist effects on drinking behavior in alcoholics, may provide more consistent evidence of a role for OPRMl in behavioral variability.