Bone Abstracts

Background: Hypophosphatemic Rickets is an inherited disorder characterized by defect in bone mineralization, mainly in long bones due to hypophosphatemia. The most common form is the X-linked form but other forms such as autosomal dominant hypophosphatemic rickets and tumor-induces osteomalacia are also described. Symptoms usually begin in infancy or early childhood and there is a large spectrum of abnormalities. The most severe form causes bowing of legs, bone deformities, bone and joint pain, growth retardation and short stature.

Presenting problem and clinical management: To present the progress both biochemical and clinical of a boy with Hypophosphatemic Rickets from diagnosis till growth completion at 17 years of age. He was born at term with a birth weight of 3550 gm, length of 50 cms (25th-50thcentile) and head circumference of 35 cms. Growth failure was noted from the age of 28 months [Length: 85 cm (5thcentile), head circumference: 52 cm (>90thcentile), arm span: 84.5 cms, leg length: 31 cm, weight: 12.600 gm]. Baseline investigations including complete blood count, arterial blood gas, liver, renal and thyroid functions, 25 (OH) vitamin D and parathormone (PTH) were within reference range but serum phosphate was low (P=2.5 mg/dl) and alkaline phosphatase high (ALP=522 U/L). Clinically, he had bowed legs and X- rays revealed bone deformities. Therapy with phosphate per os and alfacalcidol was initiated and were instructed to increase dietary calcium. The boy was reevaluated every 6 months and dose was adjusted according to the levels of serum phosphate, alkaline phosphatase and PTH. Growth velocity was also taken into consideration. Treatment goal was to keep alkaline phosphatase normal and phosphate levels above 3.2 mg/dl 2 hours postprandialy, avoiding secondary hypoparathyroidism. Although in early childhood genu valgum persisted, it was opted to proceed only with medical treatment. Bone deformity gradually improved and currently there is only minimal bowing. He entered puberty at the age of 12 yrs and today he has reached final height at 169.3 cms (25th centile) (target height: 178±5 cm).

Discussion: Meticulous monitoring of growth velocity and biochemical markers and dose adjustment can assure normal growth and avoidance of secondary hypoparathyroidism and/or nephrocalcinosis.

Disclosure: The authors declared no competing interests.