Deaf intermarriage has limited effect on the prevalence of recessive deafness and no effect on underlying allelic frequency

Concentration of disability in families: Intergenerational transmission or assortative mating?

Although studies have established that health and socioeconomic disadvantages often accumulate within families, little is known about the extent to which disability is concentrated within certain families and transmitted across generations. We use retrospective information about growing up with parent(s) or sibling(s) with a disability from the 2020 wave of the representative Survey of Health, Impairment and Living Conditions in Denmark (N = 7709). Building on this data and applying a family life course perspective, we examine if growing up with parent(s) and/or sibling(s) with a disability is associated with 1) having a disability oneself, 2) the probability of having a partner with a disability and 3) the occurrence of disability in the next generation. Our findings demonstrate that the odds of having a disability are higher among individuals who grew up with parent(s) and/or sibling(s) with a disability. While the odds of being partnered are not associated with family members' disabilities, we find a positive association between having grown up with parents with a disability and having a partner with a disability. Moreover, having a child with a disability is positively associated with one's own, parents', siblings' and partner's disabilities. We thus conclude that disability is concentrated within certain families and that both intergenerational transmission and assortative mating contribute to this concentration.

The GJB2 (Cx26) Gene Variants in Patients with Hearing Impairment in the Baikal Lake Region (Russia)

The GJB2 (Cx26) gene pathogenic variants are associated with autosomal recessive deafness type 1A (DFNB1A, OMIM #220290). Direct sequencing of the GJB2 gene among 165 hearing-impaired individuals living in the Baikal Lake region of Russia identified 14 allelic variants: pathogenic/likely pathogenic-nine variants, benign-three variants, unclassified-one variant, and one novel variant. The contribution of the GJB2 gene variants to the etiology of hearing impairment (HI) in the total sample of patients was 15.8% (26 out of 165) and significantly differed in patients of different ethnicity (5.1% in Buryat patients and 28.9% in Russian patients). In patients with DFNB1A (n = 26), HIs were congenital/early onset (92.3%), symmetric (88.5%), sensorineural (100.0%), and variable in severity (moderate-11.6%, severe-26.9% or profound-61.5%). The reconstruction of the SNP haplotypes with three frequent GJB2 pathogenic variants (c.-23+1G>A, c.35delG or c.235delC), in comparison with previously published data, supports a major role of the founder effect in the expansion of the c.-23+1G>A and c.35delG variants around the world. Comparative analysis of the haplotypes with c.235delC revealed one major haplotype G A C T (97.5%) in Eastern Asians (Chinese, Japanese and Korean patients) and two haplotypes, G A C T (71.4%) and G A C C (28.6%), in Northern Asians (Altaians, Buryats and Mongols). The variable structure of the c.235delC-haplotypes in Northern Asians requires more studies to expand our knowledge about the origin of this pathogenic variant.

Agent-Based Modeling of Autosomal Recessive Deafness 1A (DFNB1A) Prevalence with Regard to Intensity of Selection Pressure in Isolated Human Population

An increase in the prevalence of autosomal recessive deafness 1A (DFNB1A) in populations of European descent was shown to be promoted by assortative marriages among deaf people. Assortative marriages became possible with the widespread introduction of sign language, resulting in increased genetic fitness of deaf individuals and, thereby, relaxing selection against deafness. However, the effect of this phenomenon was not previously studied in populations with different genetic structures. We developed an agent-based computer model for the analysis of the spread of DFNB1A. Using this model, we tested the impact of different intensities of selection pressure against deafness in an isolated human population over 400 years. Modeling of the "purifying" selection pressure on deafness ("No deaf mating" scenario) resulted in a decrease in the proportion of deaf individuals and the pathogenic allele frequency. Modeling of the "relaxed" selection ("Assortative mating" scenario) resulted in an increase in the proportion of deaf individuals in the first four generations, which then quickly plateaued with a subsequent decline and a decrease in the pathogenic allele frequency. The results of neutral selection pressure modeling ("Random mating" scenario) showed no significant changes in the proportion of deaf individuals or the pathogenic allele frequency after 400 years.