Bone mineral density in patients with phenylketonuria

Dual energy X-ray absorptiometry was performed in 44 patients with phenylke tonuria (PKU) aged 6-29 y. The phenylalanine-restricted diet was based on a low-protein diet in combination with phenylalanine-free amino acid mixture s and phenylalanine-low casein hydrolysate in 32 patients. The 10 oldest pa tients were supplemented only with casein hydrolysate, and the youngest chi ld received only the amino acid mixture. One patient has recently come off the diet. Bone mineral density (BMD) of the lumbar spine and total BMD were measured and expressed as Z-score, i.e. the difference between the BMD of the patient and the average BMD of sex- and age-matched controls divided by the standard deviation of the control group. Normal BMD was found in 24 (5 4%) patients. Lumbar spine BMD was decreased in 20 patients and total BMD w as decreased in 14 patients. Z-scores of -1 to -2.5 were found in 14 patien ts (32%) and Z-scores of <-2.5 in 6 patients (14%). No significant correlat ion was found between total or lumbar spine BMD and daily intake of phenyla lanine from natural sources in the low-protein diet or the amount of phenyl alanine-free amino acid mixtures per kg of body weight. A significant negat ive correlation was observed between both total and lumbar spine BMD Z-scor es and the amount of casein hydrolysate supplementation per kg of body weig ht (r = - 0.45; y = 0.07 - 0.69x; p < 0.01). Longlasting dietary restrictio n in patients with PKU may increase the risk of late complications of dieta ry therapy, such as osteoporosis or trace element deficiency.