Elemental Milk Formula as a Possible Cause of Hypophosphatemic Rickets in Wiedemann-Steiner Syndrome.

Phosphate has a fundamental role in bone mineralization, and its chronic deficiency has multiple negative consequences in the body, including defects in bone mineralization that will manifest in children as rickets and osteomalacia. Here we present a young boy known to have Wiedemann-Steiner syndrome with multiple co-morbidities that necessitated gastric tube feeding. The child at 22 months was found to have hypophosphatemia and a high alkaline phosphatase level associated with rachitic skeletal manifestations that were attributed to low phosphate intake and/or gastrointestinal absorption, as there was no evidence of excessive phosphate wasting based on appropriate tubular renal re-absorption of phosphate. The primary nutritional source was an elemental amino acid-based milk formula (Neocate®) from 12 months of age. After switching from Neocate® to another elemental amino-acid based milk formula, all biochemical and radiological abnormalities returned to normal, indicating that the Neocate® formula was the possible cause of the patient’s low phosphate intake. However, in the literature, this formula-associated effect was only described in a limited number of patients. Whether or not some patient-related factors, such as the very rare syndrome described in our patient, could influence this effect warrants further exploration.