GENETIC MEDIATION OF THE CORRELATION BETWEEN PERIPHERAL-NERVE CONDUCTION-VELOCITY AND IQ

Variation in peripheral nerve conduction velocity (PNCV) and intellige nce was studied in Is-year-old Dutch twins. It has been suggested that both brain nerve conduction velocity and PNCV are positively correlat ed with intelligence (Reed, 1984) and that heritable differences in ne rve conduction velocity may explain part of the well-established herit ability of intelligence. The relationship among IQ, obtained with the Wechsler Adult Intelligence Scale, and median nerve PNCV was examined in 159 twin pairs. Genetic analyses showed a heritability of 81% for I Q and 66% for onset PNCV. The small but significant phenotypic correla tion between IQ and onset PNCV (.15) was entirely mediated by common g enetic factors. Analyses of difference scores for PNCV of this study a nd PNCV from the same subjects collected at age 16 suggest that there might still be development in PNCV in this age interval. This maturati on is highly controlled by genetic factors. It is suggested that varia tion in IQ that is associated with nerve conduction velocity becomes a pparent only after the developmental processes in peripheral nerves ar e completed. This is in line with the suggestion of increasing heritab ility of IQ in adulthood.