Radiographic bone changes in hyperphenylalaninemic children

Hyperphenylalaninemic syndromes are mostly due to inherited deficiency of phenylalanine hydroxylase. This defect leads to a severe psychomotor retardation in late diagnosed children; only prompt (within the first month of life) and adequate phenylalanine restricted dietary therapy may pre-vent the neurological damage. Previous papers described radiographic bone abnormalities (metaphyseal vertical calcified striations and spicules projecting from the metaphysis into the epiphyseal plate), mysteriously limited to the wrist, as «characteristic» features in hyperphenylalaninemic subjects together with frequent «nonspecific» bone changes as metaphyseal cupping and alteration of skeletal maturation. Whether these lesions are a consequence of a too restricted dietary treatment or due to the underlying metabolic defect rather than derived from intrauterine amino acid imbalances is still not clear. We present data concerning 120 hyperphenylalaninemic patients out of 300 referring to our Department, who underwent radiographs of the hand and wrist. No mineral deficiency was detected. Five (4.1 %) patients, all affected by classical phenylketonuria, showed the mentioned «characteristic» bone changes while 40 (33.3 %) presented with some minor «nonspecific» radiographic signs. No correlation seems to exist between bone changes and plasma phenylalanine level. Our data seem to support the hypothesis of a somehow «disease-linked» and not «nutritional» origin of bone alterations, although the possible modification of the mineral bioavailability in semisynthetic diets as well as the role of intrauterine amino acid imbalance remain to be further investigated.