Neonatal screening for phenylketonuria: III. Altered sex ratio; extent and possible causes

Abstract

In many infants with phenylketonuria (PKU) the concentration of blood phenylalanine rises only minimally during the first three days of life and infants of both sexes may be missed by screening. During this period the rate of rise of blood phenylalanine is slower in females than in males and, on the fourth day of life, significantly more males than females are discovered by screening. The ratio of males to females who are screened on the fourth day is not higher than on the previous days. The large proportion of all infants who were screened on the fourth day of life probably accounts for the previously described excess of males; females are being missed. In 12 states providing data 44.4% of all infants were screened on one of the first three days of life and 25% on the fourth day. In many infants with phenylketonuria (PKU) the concentration of blood phenylalanine rises only minimally during the first three days of life and infants of both sexes may be missed by screening. During this period the rate of rise of blood phenylalanine is slower in females than in males and, on the fourth day of life, significantly more males than females are discovered by screening. The ratio of males to females who are screened on the fourth day is not higher than on the previous days. The large proportion of all infants who were screened on the fourth day of life probably accounts for the previously described excess of males; females are being missed. In 12 states providing data 44.4% of all infants were screened on one of the first three days of life and 25% on the fourth day.