VITAMIN D RESISTANT RICKETS

Table 6.19 enlists some important indicators of non- nutritional rickets, the most important being no response to vitamin D therapy. Some important causes of resistant rickets are as follows:

Familial or primary hypophosphatemia, an X-linked dominant disease, is a leading cause of non-nutri- tional rickets due to defects in: (a) renal reabsorption

of phosphates, with consequent phosphaturia and hypophosphatemia, (b) conversion of 25(OH)D₃ into 1,25(OH)₂D₃.

Clinically, these cases usually present as toddlers with severe bow-legs and waddling gait, typically more severe in males.

Diagnosis rests on: (a) no response to vitamin D therapy, (b) similar family history, (c) heavy phosphaturia despite hypophosphatemia, and (d) absence of glucosuria, aminoaciduria and bicarbonaturia (d/d renal tubular acidosis).

Treatment includes daily phosphate supplements as Joulie solution (PO 0.5-1.0 gm/day q4hr), along with vitamin D₂ (2000 lU/kg/day) or preferably, 1,25 (OH)₂D₃ (30-60 ng/kg/day). Mega vitamin D therapy, as used in nutritional rickets, should be avoided due to the risk of hypercalcemia and nephrocalcinosis.

([§] [**]Joulie solution: 30.4 mg phosphates/ml)

Vitamin D-dependent rickets manifest at 3-6 months of age and are of two types:

• Type I, due to 25(OH)D3-1 -hydroxylase deficiency that prevents renal conversion of vitamin D into active form, and

• Type II, due to inherited end-organ resistance.

While type I may be treated with massive doses of vitamin D₂ (2-10 lac lU/day), type II needs to be treated with 1,25(OH)₂D₃ (15-30 pg/kg/day).

D/D includes other causes of hypercalcemia, e.g. chronic renal failure, hyperparathyroidism and idiopathic hypercalcemia (William's syndrome).

Treatment includes:

• Discontinue vitamin D and reduce calcium intake,

• Calcium chelators, e.g. oral Al(OH)₃ or sodium versenate for 2-3 weeks to reduce absorption,

• Cortisone 100 mg/day for 4 weeks in severe cases.

6.5