Academic journal article Mankind Quarterly

Major Intelligence Gene Tied to Myopia: A Review

Academic journal article Mankind Quarterly

Major Intelligence Gene Tied to Myopia: A Review

Article excerpt

Data are reviewed which clearly support the conclusion that axial myopia is an inherited condition following a recessive pattern of transmission. Nearsighted persons excel in terms of intelligence, several studies in developed countries having indicated a gain of 7 IQ points over the general population. It also appears that visually normal heterozygous carriers of one myopia gene enjoy brain enhancement, probably of a somewhat lower degree than occurs in homozygous myopes. It is concluded that the proposed myopia gene is primarily an intelligence factor.

Key Words: Myopia; Genetics; Intelligence.

Some investigators have attempted through population studies to identify genes involved in human intelligence, comparing results attained by various groups in test situations. One approach has been based on evaluation of ethnic differences in IQ performance, hampered by serious controversies (Herrnstein and Murray, 1994). Another strategy has focused on records from educational institutions limited to individual countries (Weiss, 1992). In either case the complexities of the available information have been essentially prohibitive in terms of any meaningful Mendelian type of analysis, and presumably many individual genes can influence mental performance.

Greater success has been achieved by starting with mutant genes that exist at unexpectedly high frequencies, perhaps maintained by favorable effects on mental ability. One such factor is the gene postulated to be involved in nearsightedness. The purpose of this paper is to assess current knowledge in that field.

Genetics of Myopia

Very young children tend to be somewhat farsighted, but development ordinarily leads to normal vision before schooling starts. Later on, usually during the maturing period, some individuals become nearsighted, unable to see distant objects clearly. The condition gradually progresses past age 20 years, averaging on the diopter lens scale around 4D, but occasionally exceeding 20D. It has been established that axial myopia, the frequent type, results from elongation of the eyeball, making the sharp image come into focus in front of the retina. Because of its appearance during the school years myopia has often been attributed to abnormal eye strains, thus being claimed to be of environmental origin. But the disorder has always been known to run only in some families, suggesting a hereditary cause. These opposing views have been a source of much debate.

Research on myopia has as a rule been relegated to eye doctors since they have the best access to the basic information. Many older ophthalmologists adhered to the hypothesis that excessive close or abnormal use of the eyes was the cause of myopic visual changes, but some early workers, in particular Steiger (1913), supported a genetic etiology. The reality was that a summary of numerous reports on monozygotic twins showed them to be generally concordant for the disorder while dizygotic twins were mostly discordant (Karlsson, 1974). A recent quite extensive twin study done in England led to a heritability estimate of 89 percent (Hammond et al. 2004), duplicating similar research reported from Australia and Denmark. Children of two clearly myopic parents also are almost invariably nearsighted.

Soon after the Mendelian principles of genetics were established a century ago, several systematic studies of myopia were conducted, demonstrating that transmission within families was consistent with recessive inheritance. Thus myopic individuals had to receive the proposed mutant factor from both parents. The first well organized research was done in Germany by Jablonski (1922) with the conclusion that the risk in sibs of index cases where one parent was affected was 50 percent while sibs with unaffected parents showed a 25 percent rate. Another family study was done in Russia and several in Japan with similar results. The most formal investigation was done in Japan by Furusho (1957) using a very sophisticated statistical procedure. …

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