Mental illness in parents of phenylketonuric children.

(1) This paper presents the results of a field study designed to investigate the hypothesis that persons presumed heterozygous for phenylketonuria are more vulnerable to mental disorder than other persons. Three-hundred-and-thirty-one persons were interviewed, including 108 parents of phenylketonuric offspring, 102 parents with non-phenylketonuric mentally retarded offspring, and 121 parents of children with cystic fibrosis. (2) Information was collected by means of a standard interview schedule which inquired into mental health problems of the interviewees as well as their parents and siblings. Interviews were coded according to an explicit code. Mental Health was evaluated by a set of indices constructed by assigning numerical values to certain items in the code and summing related items. These indices served as operational definitions of mental illness. (3) Analysis of variance was used to evaluate data derived. (4) Decreasing social class appeared to be associated with increasing scores on the indices. In addition, men and women scored significantly differently on many of the indices. In general, differences due to sex and social class were in the direction which would have been expected if the indices had been measuring the problem areas we were trying to evaluate. (5) The parents of phenylketonuric children did not score differently from the other two groups, indicating that they were not more susceptible to mental health problems than the controls, at least as measured by our operational definitions. (6) Some of the problems associated with field studies of psychiatric disease are discussed.