Abstract 663 Pulmonary: Cystic Fibrosis Poster Symposium, Tuesday, 5/4

Osteoporosis is nearly universal in patients with end-stage cystic fibrosis (CF) but the mechanisms involved in the development of this problem are unclear. The presence of bone demineralization in CF patients who do not have end-stage is uncertain but some data suggest that the bone mineral deficit may begin in pre-pubertal children. This study was undertaken to determine if osteopenia is evident in pre-pubertal children with CF and, if so, whether it is due to problems in bone formation or bone resorption. Eleven children with CF from our CF Center between the ages of 8 and 12 years and eleven non-CF controls matched by weight and gender participated in this prospective, case-control study. The mean age of diagnosis for CF was 3 months and all CF subjects were taking pancreatic enzyme supplements regularly. Bone density of the forearm, hip, and lumbar spine was measured by dual energy x-ray absorptiometry. Serum and urine samples were obtained to measure biochemical markers of bone formation (serum bone specific alkaline phosphatase and osteocalcin) and resorption (24 hour urine hydroxproline and N-telopeptide), as well as serum calcium, parathyroid hormone (PTH) and vitamin D metabolites. A three day dietary intake record was also collected. No difference was found in bone mineral content at the three skeletal sites between the two groups. The bone specific alkaline phosphatase level was less for CF subjects than controls (72 ug/L vs 85 ug/L, P=0.05). Serum osteocalcin and urine hydroxproline and N-teleopeptide levels were similar between the two groups. The CF subjects had higher median daily intake of total calories (2689 vs 1451 calories, P=0.01), calcium (1406 vs 633 mg, P=0.008), phosphorous (1722 vs 852 mg, P=0.009), and vitamin D (607 vs 151 IU, P=0.008) than that of controls. Serum 25-OH vitamin D levels were reduced in CF subjects compared to controls (22 ng/mL vs 39 ng/mL, P=0.02). 1,25 dihydroxyvitamin D level were borderline or low in 7 CF subjects and 2 controls (P=0.08). Intact PTH levels were above the upper limits of normal in 4 CF subjects and 1 control. In conclusion, pre-pubertal children with CF do not have bone mineral deficits when compared with weight and gender matched controls. However, their low vitamin D levels with high PTH levels and low bone formation may signify future problems with bone mineralization. High dietary intakes of calcium, phosphorus, and vitamin D might not prevent future osteoporosis in CF subjects.