Bone Mineral Density in Adults With Hyperphenylalaninemia

Hyperphenylalaninemia (HPA) is a rare metabolic disorder caused by a deficiency of the
enzyme phenylalanine hydroxylase (PAH). Elevated plasma levels of phenylalanine (phe) cause
mental retardation, microcephaly, delayed speech, seizures, eczema, and behavior problems.
Adequate control of the plasma levels of phe by a phe-restricted diet can prevent the
developmental and behavioral problems.

The foundation of this diet is a phe-free medical product/formula made from free amino
acids. Based on longitudinal studies, it has been reported that the most benefit is
attained by individuals who maintain a phe-restricted diet throughout life. Despite the
obvious benefits of the diet, it has been suggested that the dietary restrictions may be
associated with poor bone health in these patients. However, data supporting this has been
reported in studies with small sample sizes and/or inadequate sample populations that
include children. There is a paucity of data on bone health in adults with HPA.

The investigators propose an observational study to describe the bone health status among
adults with a diagnosis of HPA and to compare them to established normative age and
gender-specific values among healthy individuals. The investigators hypothesize that adults
with HPA will have lower bone density as measured by a dual x-ray absorptiometry (DXA) scan
compared to the established normative values.