Kinds of Information about Human Populations Needed for Monitoring

While this is in doubt, the greater emphasis must be given to the collection of human data needed to assess the mutational component in genetic disease. In this connection, it is commonly assumed (a) that about six individuals out of every hundred born alive are seriously affected at some time in their lives by known hereditary diseases or congenital disorders of unknown etiology and (b) that perhaps one-sixth to one-half of this load of morbidity may be maintained by repeated mutations. However, the uncertainties, especially with respect to the latter assumption, are great. 

Most likely to be influenced by an increase in mutation rate is the monomeric component of hereditary disease, i.e., those conditions caused by differences in single genes or chromosomes. Information on the magnitude of this component, and the fraction of it maintained by recurrent mutation, is therefore especially needed. 

So far, only one serious attempt has been made to list all genetic diseases occurring in a major geographic area, together with their frequencies among liveborn individuals and in the living population. This list was compiled nearly 15 years ago, however, and has undergone only limited revision since. 

At that time, it was usual to regard certain of the less regularly inherited diseases as due to single dominant genes with poor penetrance. This view has since been changing, and there is now reason to believe that a substantial proportion of the illnesses classified in the above reference as due to simple dominant inheritance may be multifactorial in nature. The distinction is important if, as is believed, the multifactorial conditions are relatively insensitive to changes in frequency due to alternations in the mutation rate. (See Section VIB for further discussion of this point.) 

The methods of data collection most appropriate for present purposes would therefore be designed to ease the tasks of 

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