Total Head Growth in Patients with Phenylketonuria Diagnosed by Newborn Screening Test

Background: Phenylketonuria is an inborn error of phenylalanine metabolism caused by phenylalanine hydroxylase enzyme deficiency. It is a relatively common disorder that is inherited as an autosomal recessive disease. Phenylketonuria can be diagnosed by newborn screening tests. The diagnosis is established when a plasma phenylalanine concentration persistently above 120 μmol/phenylketonuria can cause microcephaly, intellectual disability, attention deficit hyperactive disorder, epilepsy, and eczema due to the accumulated toxic effect of phenylalanine in the blood. Objective: The aim of this study was to determine whether phenylalanine control can improve head growth in early-diagnosed and treated children. Materials and Methods: The head circumference records of 28 early detected patients with phenylketonuria at diagnosis and at 3-month intervals till the age of 3 years were studied. These measurements were compared between two groups those with phenylalanine median readings below 360 μmol/L but never above 600 μmol/L as the accepted control group and those with readings higher than 600 μmol/L as the poor control group. Results: The total number of children included in this study was 28 children. The patient’s age ranges from 3 years to 8 years. Males represented 57.14% of them. The median age at diagnosis and starting treatment was 18.5 days and 58 days, respectively. In this study, higher occipitofrontal circumference z -score readings were noticed among children with relatively lower phenylalanine levels at diagnosis (38.89% of them had z -score greater than zero) compared to those with higher Phenylalanine level (only 20% of them had z -score greater than zero) with a statistically significant difference. The same finding was observed at 3 years of age (head circumference z -score more than zero in 27.28% of accepted phenylalanine level control vs. 10% of poor phenylalanine level; however, the difference exceeded the acceptable level of significance ( P = 0.057)). Conclusion: In patients with phenylketonuria diagnosed by newborn screening test, the higher the phenylalanine level at diagnosis, the smaller the head size compared with those with lower phenylalanine levels. At 3 years of age, the head growth of those with stricter phenylalanine control does not vary greatly from those with less strict control.