HEREDITY OF THE CONGENITAL PROFOUND DEAFNESS

ANALYSIS OF 25 PAIRS OF DEAF TWIN

Abstract

Original index of 53 pairs of deaf twin, who had graduated from schools for the deaf in Japan, was represented as the subject of this study. Such investigations as pure tone audiogram, routine physical examinations and genetic analysis were essential for identifying the nature of congenital deafness. The zygosity diagnosis was based on the principle of the probability method. After preliminary work-ups of 53 pairs of twin, 25 suitable pairs were selected for the evaluation of genetical analysis for the profoundly deaf. Ratio of monozygotic to dizygotic twins was 17:8. The concordance of profound deafness was seen 88.2 per cent in monozygotic twins, while only 50.0 per cent in dizygotic twins. Penetrance of this gene was 0.94. The difference of hearing loss between each of twin of monozygotic pairs were significantly larger than that of dizygotic pairs. Incidence of inbreeding coefficient in parents of 25 pairs of twin was relatively higher than in general population. This study indicated important role of genetical control in congenital profound deafness.