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Health

One "deafness" allele = better healing?

Gene ExpressionBy Razib KhanMay 9, 2006 12:19 AM

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Weird finding:

A mutation in a gene commonly associated with deafness can play an important part in improving wound healing, a scientist told the annual conference of the European Society of Human Genetics in Amsterdam, The Netherlands, today (Monday 8 May 2006). Dr. Stella Man, from the Institute of Cell and Molecular Sciences, Queen Mary's University, London, UK, said that the discovery may have implications for the treatment of a wide range of wounds, including post-surgery. ... Professor Kelsell was the first to describe the link between Cx26 mutations and deafness in 1997. "Since many people carry this mutation", Dr. Man said, "and people who have just one such mutation are not deaf, we felt that there might be some evolutionary advantage to it, so we decided to investigate how the mutation affected the ability of cells to communicate with each other in the epidermis where Cx26 is also expressed."

I guess they are positing heterozygote advantage. The only thing is one assumes that selection for heterozygosity would be a) strong b) recent, because being deaf is really maladaptive, and modifier genes would have evolved to mask that trait given enough time. If this is a standard Mendelian trait, than the frequency of the homozygotes (deaf) in the population would be q^2, where p = wild type, and q = mutant. If a pq combination is more fit than either pp or qq, its increase in frequency would be buffered by the fact that as q increases (ergo, the % who are pq increases) the number who are qq also increases. In a situation where you want to maximize pq, the heterozygote, and the homozygotes have equal fitness, you'd have p = .5 and q=.5, so that the frequency of the heterozygotes would be 2pq, or 50%. But, you'd have 25% who are qq, which is not good, since we know they are maladptive.... Anyway, JP is at the conference where this was presented, so perhaps he'll have more details soon. Update: For overdominance/heterozygote advantage.... pq (heterozygote) = 1 pp (homozygote = 1 - s1 qq (homozygote) = 1- s2 Where s = selection coefficient Equilibrium frequency of p is = s2 / ( s1 + s2) Assume that pp (wild type) has a fitness of 0.95 (ergo, s1 = -0.05) and qq (deafness) has a fitness of 0.5 (ergo, s2 = -0.5). You get a frequency of p as 91%, so that heterozygotes are 16.5% of the population. So, this paper is of interest, High carrier frequency of the 35delG deafness mutation in European populations. Genetic Analysis Consortium of GJB2 35delG:

Congenital deafness accounts for about 1 in 1000 infants and approximately 80% of cases are inherited as an autosomal recessive trait. Recently, it has been demonstrated that connexin 26 (GJB2) gene is a major gene for congenital sensorineural deafness. A single mutation (named 35delG) was found in most recessive families and sporadic cases of congenital deafness, among Caucasoids, with relative frequencies ranging from 28% to 63%. We present here the analysis of the 35delG mutation in 3270 random controls from 17 European countries. We have detected a carrier frequency for 35delG of 1 in 35 in southern Europe and 1 in 79 in central and northern Europe. In addition, 35delG was detected in five out of 376 Jewish subjects of different origin, but was absent in other non-European populations. The study suggests either a single origin for 35delG somewhere in Europe or in the Middle East, and the possible presence of a carrier advantage together with a founder effect. The 35delG carrier frequency of 1 in 51 in the overall European population clearly indicates that this genetic alteration is a major mutation for autosomal recessive deafness in Caucasoids. This finding should facilitate diagnosis of congenital deafness and allow early treatment of the affected subjects.

I doubt it is at equilibrium.... Related:Hardy-Weinberg Equilibrium.

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