Growth rate in children with vitamin-D-dependent rickets in relation to 1-alpha-hydroxyvitamin D3 dosage

Growth rate of five children with vitamin D-dependent rickets was analyzed during the long-term treatment with an active analog of vitamin D3. Considerable increase in growth rate together with the improvement of biochemical values and radiological pattern took place during the initial phase of administration of 1-hydroxyvitamin D3. During the maintenance treatment of long duration with 1-hydroxyvitamin D3 both the acceleration of growth and catch-up growth persisted. However, in 4 among 5 children studied an inhibition of growth was observed during different periods of time. Only in one boy was this connected with the conclusion of the process of physiological growth. In three remaining children a slow-down in growth rate appeared during the pre-pubertal period or was the effect of lowering the dose of 1-hydroxyvitamin D3 as an countermeasure to hypercalciuria. In such cases inhibition of growth was caused by the administration of too small a dose of 1-hydroxyvitamin D3 in relation to the requirement. In all cases the appearance of biochemical features of rickets aggravation, such as low blood serum phosphate concentration and elevated alkaline phosphatase activity, preceded the observable inhibition of growth. The results obtained allow us to conclude that the inhibition of growth observed during the long-term treatment of rickets with 1-hydroxyvitamin D3 may be regarded as the first signal of inadequate dosage of 1-hydroxy vitamin D3.