Bone mineral status in children with phenylketonuria--relationship to nutritional intake and phenylalanine control.

The mineral status in phenylketonuria (PKU) was measured by single-photon densitometry of the distal radius and plasma concentrations in 26 subjects. Bone mineral content increased normally with age in the younger children despite strict dietary restrictions. Subjects aged greater than 8 y, however, were frequently below the normal curve for bone mineral content. Blood phenylalanine concentrations were significantly higher in the older group of subjects and this correlated with decreased compliance with dietary prescriptions. PKU children had significantly decreased plasma concentrations of alkaline phosphatase, magnesium, and parathyroid hormone. Subnormal concentrations of plasma zinc and plasma and red blood cell (RBC) copper were common, but RBC zinc was normal. We conclude that compliance with dietary therapy for PKU is associated with normal bone mineral development in young children. Older patients with PKU who follow the diet less carefully are at risk for low bone mineral content.