Congenital rickets. Study of the evolution of secondary hyperparathyroidism.

A case of congenital rickets of nutritional origin is described in a light-for-date premature infant (gestational age 34 weeks, birthweight 1 100 g). X-rays of the long bones showed spread, frayed and cupped metaphyses at birth and at the age of 16 days. Serum calcium was 8.2 mg/100 ml, phosphorus 3.4 mg/100 ml and alkaline phosphatase (A.P):323 IU/ml (N less than or equal to 200) at the age of 3 days. Very high level of serum immunoreactive parathroid hormone (iPTH) was found at the age of 16 days=295 micronlEq/ml (N less than or equal to 50). Evidence of maternal vitamin D deficiency was demostrated by low plasma 25-hydroxycholecalciferol (25-OH-CC):1.0 ng/ml (N:13.2+/-4.2) soon after delivery; it was found to be normal (10.2 ng/ml) six months later. Ca infusion (15 mg/kg/3 h) resulted in a marked fall of serum iPTH (280 to 84 micronlEq/ml). Administration of vitamin D2 (2400 IU/day for 10 days) induced some healing of the metaphyses; A. P. remained elevated (400 IU/ml); plasma 25-OH-CC was normal 10.2 ng/ml and serum iPTH was 115 micronlEq/ml. When 25-OH-CC was given orally for ten days (15 microng/day), plasma 25-OH-CC rose to 64.5 ng/ml with a minor change of serum iPTH (94 micronlEq/ml); X-rays of the bones showed osteoporosis. These results suggest a reduced convertion of 25-OH-CC into 1-25-(OH)2-CC.