Bone mineral status in children with phenylketonuria under treatment

Abstract

Bone mineral status was assessed in 48 children with phenylketonuria (PKU) (20 M, 28 F, aged 2.5‐17 y). Bone density was measured in the distal third of the right forearm using single photon absorptiometry and was expressed as ±SD with respect to age‐ and gender‐matched controls. Serum calcium (Ca), magnesium (Mg), phosphorus (P), alkaline phosphatase (ALP), parathyroid hormone and 25‐hydroxyvitamin D were measured in morning samples. The ratios of urinary Ca/creatinine (UCa/ UCr), UP/UCr, UMg/UCr and hydroxyproline (OH‐Pr)/UCr were calculated in urine samples collected over a period of 3h. Patients' data were compared with those of 50 controls (22M, 28F, aged 3‐15y). The data showed severe osteopenia (below ‐2 SD) in 22/48 patients. Bone loss was more prominent in patients over 8y old. Bone density correlated significantly with age (r=– 0:56, p < 0.001) and with Phe (r=– 0:49, p < 0.007) but did not correlate with the other biochemical indices studied. Comparing PKU children with controls, significantly higher serum calcium and magnesium (p= 0:04, p< 0.001, respectively), lower ALP (p= 0:01), higher UCa/UCr ratio (p < 0.001), lower UP/UCr (p < 0.001) and lower UOH‐Pr/UCr (p < 0.001) were found. Dietary compliance was poor in patients over the age of 8y, as only 3/22 of ≤ 8y had mean serum phenylalanine >10mgdl−1, in contrast to 21/26 in the older group. It is clear from the data that osteopenia is commonly found in PKU patients from early life. The biochemical data indicate a metabolic state of low bone turnover in PKU patients. In conclusion, a better, more restricted diet may correct osteopenia.