Protein insufficiency and linear growth restriction in phenylketonuria.

Objectives: To study the role of protein sufficiency, age, calorie sufficiency, and phenylalanine levels in children with phenylketonuria (PKU) and determine how these affect linear growth.

Methods: Age, growth measures, plasma prealbumin, and mean phenylalanine levels were analyzed from a chart review of 38 children with early and continuously treated PKU.

Results: A regression model was calculated investigating the effects of prealbumin, age, body mass index, and mean phenylalanine level on height. In this model, plasma prealbumin of <20 was associated with a loss of 45 height percentiles, whereas age and body mass index also had smaller but statistically significant effects. Prealbumin was correlated with height and age such that children with lower prealbumin levels were shorter and younger. There was no significant correlation between age and height or mean plasma phenylalanine level and height. A prealbumin level of 20 mg/dL appeared to constitute a threshold level, below which height growth was very significantly impaired.

Conclusions: There is a strong relation between protein insufficiency, as determined by plasma prealbumin levels, and linear growth impairment. We suggest that a plasma prealbumin level of at least 20 mg/dL is necessary for optimal growth in children with PKU.