A Case of Vitamin D Dependency Type I

抄録

Vitamin D dependency type I is a disease characterized by hypocalcemia and rickets in early infancy. We report the case of a female patient diagnosed as having vitamin D dependency type I by the clinical features and the PTH loading test after a low calcium diet. The patient was referred to Osaka University Hospital when she was 2 years 2 months old. She had slight bowing of the legs but no hypocalcemia. Her serum concentrations of 25-hydroxyvitamin D (25OHD) and 1, 25 (OH) ₂D were 18.1 ng/ml and 14 pg/ml, respectively. After 3 days on a low calcium diet, the PTH loading test was performed. Neither the low calcium diet nor the injection of PTH increased serum 1, 25 (OH) ₂D levels, while serum 1, 25 (OH) ₂D levels were significantly increased in normal controls. When active vitamin D metabolites were not administered, serum alkaline phosphatase (ALP) and PTH increased gradually to 1090 U/1 and 1120 pg/ml, respectively. After administration of a physiological dose (0.08μg/kg/day) of 1α-hydroxyvitamin D₃ (1αOHD₃), the serum ALP and PTH levels returned to normal.
The blunted response of serum 1, 25 (OH) ₂D concentration to the PTH loading test as well as to the low calcium diet, and the necessity for a physiological dose of 1αOHD₃, suggest that she had a partial defect in renal 25OHD₃-1α-hydroxylase activity.