what is the cause of this case.. the cause of hypophosphatemic rickets

what is the cause of this case:
Serum ca …… normal
Serum phosphate….. decreased
Urine ca…… decreased
Urine phosphate ………. Increased
Alkaline phosphatase …….. increased
A renal disfunction
B gene mutation
c. malabsortion syn.
d. thyroid adenoma
(b) the cause of hypophosphatemic rickets