Advances in the Genetic Etiology of Hearing Impairment

A recently published article in Experimental Biology and Medicine (Volume 246 Issue 13, July, 2021) describes a new genetic mutation linked to hearing impairment. The study, led by Dr. Ambroise Wonkam in the Division of Human Genetics, Faculty of Health Sciences at the University of Cape Town (South Africa), reports a variant of the DMXL2 gene in Cameroonian families with hearing impairment.   
The inability to hear properly in one or both ears impacts nearly 6% of the global population. Hearing impairment can be caused by environmental or genetic factors. However, establishing a definitive genetic cause can prove difficult in some cases. Approximately 70% of genetic related hearing impairment cases are non-syndromic and occur without the presence of other clinical factors. Over 120 genes have been linked to non-syndromic hearing impairment. While most cases in Europe and Asia can be traced to variants in a single gene, the GJB2 gene, the etiology of African non-syndromic hearing impairment cases is unresolved.
In this study, Dr. Wonkam and colleagues used direct sequencing methods to analyze DNA samples from a Cameroonian family with non-syndromic hearing impairment (NSHI). A mono-allelic missense variant [NM_015263.5:c.918G>T; p.(Q306H)] was identified in the DMXL2 gene in this family. This variant was present in the heterozygous state in the affected mother and the two affected children (one male and one female), and absent from the other two unaffected children (one male and one female). The variant was absent from many genome databases, over 120 control individuals from Cameroon, and 112 isolated cases of NSHI from Cameroon. This is the first report implicating DMXL2 in NSHI in Africans and confirms a previous report of this variant in China. Dr. Wonkam said, “DMXL2 is now a confirmed NSHI candidate gene in Cameroon, and more studies are needed to assess its implication in other populations around the world.”
Dr. Steven R. Goodman, Editor-in-Chief of Experimental Biology & Medicine, said “Dr. Wonkam and colleagues have identified a mono-allelic variant in DMLX2, also called rabconnectin-3a (RC3), in a Cameroonian family with hearing impairment. A similar variant was previously found in a Han Chinese family. It is very interesting that RC3 is found on inner ear hair cells and is a part of a synaptic vesicle protein complex involved in Ca2+-dependent neurotransmitter release in brain. Future studies aimed at a detailed understanding of the role of DMXL2 in hearing impairment is warranted.”
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Source: Experimental Biology and Medicine