The Incidence of Developmental and other Genetic Abnormalities

Summary

Possibly 6 per cent of all new born infants have a developmental anomaly— sometimes severe, sometimes relatively mild, at times treatable but often not. The commonest anomalies are those of the central nervous and of the cardiovascular systems and of mentation. Biochemically defined errors, though singly rare, are relatively frequent in the aggregate and chromosome disorders with variable degrees of developmental anomaly are even more frequent. In addition many conceptuses that are chromosomally abnormal are spontaneously aborted and quite a few die in the perinatal period.

Single gene abnormalities account for about one-third of developmental errors discovered or present at birth and chromosome errors for about one-twelfth. In a further substantial proportion of developmental errors the cause is not a single gene anomaly: multiple genes and their alleles interact between themselves and with the environment to produce abnormal development and the relative contributions of nature and nurture can vary a great deal.

Expanded from a paper given to the Royal Society of Medicine, Section of Obstetrics and Gynaecology with Section of Paediatrics, on 23 March 1973.