In certain mental deficiencies an association has been established between the mental defect and a genetically determined biochemical abnormality. For instance, in the phenylketonuric person there is a specific biochemical defect, with the mode of inheritance well known; in others, e. g., the Mongoloid patient, a biochemical defect may be present and the question of inheritance is still debated. Though patients with known biochemical defects constitute only a small portion of all the mental defectives, the number of specific syndromes identified is increasing as the result of continuing research. This rapidly expanding knowledge warrants a summary, with a hope that it will stimulate clinical search for additional patients and entities.In those conditions where the biochemical abnormality is well understood, the basic mechanism is a genetically determined defect in enzyme function, which manifests itself in deviant metabolism of a specific nutrient or substrate. Our classification is in accordance with
WRIGHT SW, TARJAN G, LIPPMAN RW, PERRY TL. Etiologic Factors in Mental Deficiency: Errors of Metabolism That May Lead to Mental Deficiency. AMA Am J Dis Child. 1958;95(5):541–562. doi:10.1001/archpedi.1958.02060050545013
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