Research in the Etiology of Down's Syndrome Intricacies and Pitfalls

Abstract

Cytological studies have shown that Down's syndrome (“ mongolism ”) is the result of a chromosomal anomaly which occurs either in one of the parent's germ cells or at a very early stage in (embryonic) development of the affected individual. The chromosomal anomaly involves the occurrence of a third number 21 chromosome, in addition to the normal complement of two, either separately (i. e., trisomy-21) or attached to one of the other acrocentric chromosomes (i. e., translocation to one of the chromosomes numbered 13-15 or 22 — Denver Report, 1960). Epidemiological studies have indicated that numerous factors are related to, and may affect, incidence of the chromosomal anomalies resulting in Down's syndrome. Studies by Collmann and Stoller (1962a, b) imply fluctuations of annual incidence with a 5-6 year periodicity, a higher incidence in urban compared to rural areas and a clusteting of affected births in certain geographic regions. Collmann and Stoller postulated an “ infectious agent, probably a virus ”, to account for their data. No connection, however, can yet be drawn between such a hypothesis and the established cytogenetic anomaly. Periodic fluctuations in incidence, which are characteristic of recurrent epidemics (Gordon, 1962), have also been reported for congenital anomalies other than Down's syndrome, such as anencephaly, spina bifida, and hydrocephaly (Collmann and Stoller, 1962b; Guthkelch, 1962; Alter, 1962; Slater, Watson and McDonald, 1964).