Assessment of Anthropometric Indices in Patients with Phenylketonuria

Dietary phenylalanine restriction is the main treatment of phenylketonuria (PKU, OMIM 261600). There are a number of studies which have demonstrated growth retardation in these patients, and some are in contrast. This study was performed to assess the growth parameters of treated PKU patients.

This cross-sectional study was performed between 2015 and 2017 to compare growth indices in PKU patients in our clinics with normal age and sex matched controls. Weight, height, head circumference (HC), weight for height and BMI (weight/height²) were measured and converted into Z-scores. We assessed differences between patients and controls' anthropometric indexes in all patients and separately in patients who were diagnosed by newborn screening program and patients who were diagnosed after presentation of clinical manifestations in comparison with age and sex-matched controls. Also, this difference was assessed separately in patients aged two years and less. Correlations between pretreatment plasma phenylalanine concentrations mean plasma phenylalanine concentrations and anthropometric parameters were analyzed in the patients.

Overall, 209 under-treatment PKU patients (103 males, 106 females; mean age 9.29 ± 8.7 years) and 216 controls (109 males and 107 females; mean age 8.98 ± 8.62 years) matched in terms of age, sex and birth weight were enrolled in this study. In general, 130 patients were diagnosed by newborn screening and 79 were diagnosed when they became symptomatic before the screening program. A significant difference (p=0.000) was found only in HC z-score and weight for height z-score in comparison with the control group, when we assessed all patients. We did not find any significant differences in any of the anthropometric indexes between cases and controls who were aged 2 years old and less. Head circumference SDS and weight for height SDS were significantly different when patients and controls who were more than 2 years old were compared. Mean HC was significantly lower in patients, while BMI SDS, weight SDS, and weight for height SDS were significantly higher in PKU patients in comparison with the control group when patients who were diagnosed in newborn screening were assessed. Head circumference SDS, BMI, height SDS and difference between patients' height SDS and mid parental height SDS had significantly lower mean scores in comparison with those of the control group, while mean weight SDS was significantly higher compared to controls when patients who were diagnosed after clinical presentation were assessed. Mean phenylalanine was not correlated with anthropometric indices, while there was a correlation between pretreatment phenylalanine and HC.

Disparities in anthropometric indexes changes observed in different studies may be due to diverse diet protocols, availability of various specific products and micronutrient substitutes.