High incidence also is reported in the Yemenite Jewish population, as well as in regions of northern and eastern Europe, Italy, and China. Psychological problems, including agoraphobia and other disorders, have been reported in individuals both on and off dietary treatment. Worldwide, PKU is most common in Caucasians and Asians. No sex predilection exists. Consider PKU at any age in an individual who is developmentally delayed or mentally retarded because infants are missed by newborn screening programs on rare occasions.
Most individuals appear normal at birth.
If newborn screening fails, progressive developmental delay is the most common presentation. Other findings in untreated children in later infancy and childhood may include vomiting, mousy odor, eczema, seizures, self-mutilation, and severe behavioral disorders. Occasionally, deterioration of cognitive performance or motor skills also may be present. IQs may drop by 10 points or more if the diet is stopped in mid childhood. The enzyme locus is on chromosome arm 12q.