Hearing Impairment Overview in Africa: the Case of Cameroon

Abstract

The incidence of hearing impairment (HI) is higher in low- and middle-income countries when compared to high-income countries. There is therefore a necessity to estimate the burden of this condition in developing world. The aim of our study was to use a systematic approach to provide summarized data on the prevalence, etiologies, clinical patterns and genetics of HI in Cameroon. We searched PubMed, Scopus, African Journals Online, AFROLIB and African Index Medicus to identify relevant studies on HI in Cameroon, published from inception to 31 October, 2019, with no language restrictions. Reference lists of included studies were also scrutinized, and data were summarized narratively. This study is registered with PROSPERO, number CRD42019142788. We screened 333 records, of which 17 studies were finally included in the review. The prevalence of HI in Cameroon ranges from 0.9% to 3.6% in population-based studies and increases with age. Environmental factors contribute to 52.6% to 62.2% of HI cases, with meningitis, impacted wax and age-related disorder being the most common ones. Hereditary HI comprises 0.8% to 14.8% of all cases. In 32.6% to 37% of HI cases, the origin remains unknown. Non-syndromic hearing impairment (NSHI) is the most frequent clinical entity and accounts for 86.1% to 92.5% of cases of HI of genetic origin. Waardenburg and Usher syndromes account for 50% to 57.14% and 8.9% to 42.9% of genetic syndromic cases, respectively. No pathogenic mutation was described in GJB6 gene, and the prevalence of pathogenic mutations in GJB2 gene ranged from 0% to 0.5%. The prevalence of pathogenic mutations in other known NSHI genes was <10% in Cameroonian probands. Environmental factors are the leading etiology of HI in Cameroon, and mutations in most important HI genes are infrequent in Cameroon. Whole genome sequencing therefore appears as the most effective way to identify variants associated with HI in Cameroon and sub-Saharan Africa in general.

Sensitivity and specificity of three hearing screening protocols in the school setting

“…This hearing problems are similar to previous results obtained in other Brazilian cities, such as São Luís (MA) 37 (24.3% of children from 7 to 9 years old) and Goiânia (GO) (24% of children from 7 to 14 years old) 34 . However, they are larger than those observed in other studies performed in more developed regions of Brazil 26,36,38 and other countries 6,7,8,13,14 . The differences in prevalence rates are due, in part, to the great variability in the procedures, methods, and techniques of the auditory screening tests performed and in the adopted pass and fail criteria of these procedures 7-,9 .…”

“…Another study 7 noted the great variability in the prevalence of hearing loss in children, from 1.4% (regarding 29 countries) to 17.5% (Netherlands). The same was found in Africa 8 and evidenced in a systematic review 9 . Although there is variability, it is evident that hearing loss in children is common 7 and has important impacts on their development.…”

Bi-Allelic Novel Variants in CLIC5 Identified in a Cameroonian Multiplex Family with Non-Syndromic Hearing Impairment

“…When occurring in childhood, HI is associated with impaired language acquisition, learning, and speech development, and affects ~34 million children worldwide (World Health Organisation) [ 2 ]. Approximately 30 to 50% of HI cases in Africa have a genetic origin [ 3 , 4 ]. Non-syndromic hearing impairment (NSHI) accounts for about 70% of HI cases of genetic origin and is inherited on an autosomal recessive (AR) mode in approximately 80% of cases [ 5 ].…”

“…Variants in GJB2 and GJB6 genes, which are the major contributors to NSHI in Europeans, Asians, and Arabs, are infrequent in most populations of African descent, with a prevalence close to zero [ 6 , 7 , 8 ]. NSHI is highly genetically heterogeneous [ 3 , 4 ]. To date, about 170 loci and 121 genes have been identified as being associated with NSHI (hereditary hearing loss homepage; Appendix A ).…”

Whole exome sequencing reveals pathogenic variants inMYO3A,MYO15AandCOL9A3and differential frequencies in ancestral alleles in hearing impairment genes among individuals from Cameroon

“…Mutations in the connexin genes GJB2 and GJB6 have been shown to account for most of genetic-associated HI among European, Asian and North American populations ( 13–15 ). However, a few studies investigated the genetic cause of HI among Africans ( 7 , 9 , 16–22 ), with most of them showing that GJB2 and GJB6 may not always be the important contributors, with the exception of Ghana, where the GJB2 -R143W founder mutation accounts for 25·9% of HI cases among families segregating autosomal recessive NSHI (ARNSHI) ( 23 ).…”