Volume 1

Principles and practice of medical genetics / editors, Alan E.H. Emery, David L. Rimoin ; assistant editor, Jeffrey A. Sofaer ; editorial assistant, A.P. Garber ; foreword by Victor A. McKusick.

Date:
1983
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Principles and practice of medical genetics / editors, Alan E.H. Emery, David L. Rimoin ; assistant editor, Jeffrey A. Sofaer ; editorial assistant, A.P. Garber ; foreword by Victor A. McKusick. Source: Wellcome Collection.

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    misleadingly low. If we include late manifesting diseases such as monogenic hypercholesterolaemia (2/1000), Huntington chorea (0.5/1000), polycystic kidney disease (0.8/1000) and neurofibromatosis (0.4/1000), the overall incidence of autosomal dominants is about 7.0 per 1000, autosomal recessives about 2.5 per 1000 and X-linked disorders about 0.5 per 1000 (Carter, 1977). These over all figures however only apply to Western countries where most of the surveys have so far been carried out. It has to be remembered that there are considerable eth nic and geographic variations in the incidence of some unifactorial disorders (e.g., cystic fibrosis, sickle cell dis ease, Tay-Sachs disease, etc.). With regard to major congenital abnormalities, esti mates of incidence are in general more reliable in pop ulations where the majority of babies are delivered in hospitals. The overall incidence in most populations is about one in fifty, but there are considerable ethnic, geo graphic and social variations in the case of individual malformations. For example talipes equinovarus is some six times commoner among Maoris of Polynesian descent than among Europeans. A particularly striking example of geographical variation in incidence is provided by the neural tube defects (anencephaly and spina bifida) where the incidence among the Irish is some ten times greater than among, for example, Blacks in North America. Geographical variations in the incidence of anencephaly, where data are somewhat more reliable than for the related but milder condition spina bifida, are illustrated in Fig. 1.1. GENETIC DISEASE AS A CAUSE OF CHILDHOOD MORTALITY In many Western countries, since the turn of the cen tury, advances in medicine and public health have resulted in a gradual decline in the contribution of envi ronmental factors to morbidity and mortality. Infectious diseases have decreased and nutritional deficiencies are now uncommon. The result of these changes has been to throw genetic disorders into greater prominence. These changes are well illustrated in data from surveys of the causes of childhood deaths in various United King dom hospitals over the last sixty to seventy years (Table 1.1). The picture is completely different from that seen at present in Third World countries. For example, in Madras, in 1976, one of us (AEHE) found that over 95% of childhood deaths in hospitals were due to non-genetic causes, usually infectious diseases, and less than 5% were due to genetic causes. No doubt with improvements in living conditions and public health, the pattern in these countries will gradually change and eventually become similar to that in more advanced countries. GENETIC DISEASE AND MORBIDITY An idea of the contribution of genetic disease to morbid ity can be judged from the results of several surveys in which the prevalence of such diseases has been estimated among paediatric and adult inpatients (Table 1.2). At