The incidence of phenylketonuria in Thailand.

Phenylketonuria (PKU) is a congenital defect involving failure to metabolize phenylalanine to tyrosine because of the absence of phenylalanine hydroxylase. Untreated PKU causes severe mental retardation, musty odor, hyperactivity, seizures, eczema and hypopigmentation. Without therapy, the child may develop with an IQ of less than 20. Restricting dietary phenylalanine before the onset of brain damage is necessary, to maintain the phenylalanine concentration at 3-8 mg/dl. Thirteen thousand three hundred and ninety-seven mentally retarded outpatients, aged 4 months to 24 years, from the year 1963 to 1987 were studied for PKU. Seven patients had positive PKU test by ferric chloride test and Phenistix, six PKU confirmed by paper chromatography. Two PKU by fluorometry and one PKU by amino acid analyzer. The incidence is 1:1,900 mentally retarded patients or 1:1,200,000 population. So, the incidence seems to be lower than in other countries which have neonatal screening for PKU. Because early diagnosis is essential in order to avoid the severe effects of PKU, neonatal screening has become widespread in the U.S., Australia, Great Britain, and other European Countries. The incidence of 1 PKU out of 1:1,200,000 Thai population seems to be not important enough for initiation of a PKU screening program in Thai newborns.