Table_2_GJB2 and GJB6 Mutations in Non-Syndromic Childhood Hearing Impairment in Ghana.docx

Our study aimed to investigate GJB2 (connexin 26) and GJB2 (connexin 30) mutations associated with non-syndromic childhood hearing impairment (HI) as well as the environmental causes of HI in Ghana. Medical reports of 1,104 students attending schools for the deaf were analyzed. Families segregating HI, as well as isolated cases of HI of putative genetic origin were recruited. DNA was extracted from peripheral blood followed by Sanger sequencing of the entire coding region of GJB2. Multiplex PCR and Sanger sequencing were used to analyze the prevalence of GJB2-D3S1830 deletion. Ninety-seven families segregating HI were identified, with 235 affected individuals; and a total of 166 isolated cases of putative genetic causes, were sampled from 11 schools for the deaf in Ghana. The environmental factors, particularly meningitis, remain a major cause of HI impairment in Ghana. The male/female ratio was 1.49. Only 59.6% of the patients had their first comprehensive HI test between 6 to 11 years of age. Nearly all the participants had sensorineural HI (99.5%; n = 639). The majority had pre-lingual HI (68.3%, n = 754), of which 92.8% were congenital. Pedigree analysis suggested autosomal recessive inheritance in 96.9% of the familial cases. GJB2-R143W mutation, previously reported as founder a mutation in Ghana accounted for 25.9% (21/81) in the homozygous state in familial cases, and in 7.9% (11/140) of non-familial non-syndromic congenital HI cases, of putative genetic origin. In a control population without HI, we found a prevalent of GJB2-R143W carriers of 1.4% (2/145), in the heterozygous state. No GJB2-D3S1830 deletion was identified in any of the HI patients. GJB2-R143W mutation accounted for over a quarter of familial non-syndromic HI in Ghana and should be investigated in clinical practice. The large connexin 30 gene deletion (GJB2-D3S1830 deletion) does not account for of congenital non-syndromic HI in Ghana. There is a need to employ Next Generation Sequencing approaches and functional genomics studies to identify the other genes involved in most families and isolated cases of HI in Ghana.

本研究旨在探究加纳地区与非综合征性儿童听力损失（hearing impairment, HI）相关的GJB2（间隙连接蛋白26，connexin 26）及GJB2（间隙连接蛋白30，connexin 30）突变，同时明确该地区听力损失的环境诱因。本研究对1104名就读于聋校的学生的医疗档案进行了回顾性分析，同时招募了存在听力损失家族聚集现象的家系，以及疑似遗传源性的孤立性听力损失病例。从外周血中提取DNA后，对GJB2的全部编码区开展桑格测序（Sanger sequencing）；采用多重聚合酶链式反应（Multiplex PCR）结合桑格测序，分析GJB2-D3S1830缺失的检出率。本研究共确认97个存在听力损失聚集现象的家系，涉及235名受累个体；同时从加纳11所聋校中招募了166例疑似遗传源性的孤立性听力损失病例。环境因素（尤其是脑膜炎）仍是加纳地区听力损失的主要致病诱因。男女患病比例为1.49:1。仅59.6%的患者在6至11岁年龄段接受了首次全面听力损失检测。几乎所有受试者均为感音神经性听力损失（99.5%，n=639）。多数患者为语前听力损失（68.3%，n=754），其中92.8%为先天性听力损失。家系分析显示，96.9%的家族性病例呈常染色体隐性遗传模式。此前被报道为加纳奠基者突变（founder mutation）的GJB2-R143W突变，在家族性病例中以纯合状态存在的占比为25.9%（21/81）；在疑似遗传源性的非家族性非综合征性先天性听力损失病例中占比为7.9%（11/140）。在无听力损失的对照人群中，我们发现GJB2-R143W突变的杂合携带者比例为1.4%（2/145）。未在任何听力损失患者中检测到GJB2-D3S1830缺失。GJB2-R143W突变在加纳家族性非综合征性听力损失病例中占比超过四分之一，应在临床实践中纳入常规筛查项目。间隙连接蛋白30基因大片段缺失（GJB2-D3S1830缺失）并非加纳地区先天性非综合征性听力损失的致病因素。亟需采用下一代测序（Next Generation Sequencing）及功能基因组学（functional genomics）研究手段，以鉴定加纳地区大多数听力损失家系及孤立病例中涉及的其他致病基因。