Pycnodysostosis: some aspects concerning kinetics of calcium metabolism and bone pathology

A 23-year-old white woman suffering pycnodysostosis whose parents and five siblings were unaffected was investigated. Chromosomal morphology was normal. Histologic examination of a biopsy specimen obtained from the distal phalanx of the left thumb, corresponding to an area on an x-ray film of osteolysis, showed a fibrous dysplasia-like picture. Kinetic studies of calcium metabolism revealed that exchangeable pool size, turnover, and bone accretion rate were all decreased. Intestinal calcium absorption was investigated simultaneously by a double isotope technique and by deconvolution of the plasmatic specific activity curve of 47Ca given per os. Results obtained by both methods coincided in that values were found to be similarly increased. Endogenous fecal calcium was also determined and revealed a similar increase. Some physiopathological implications of these findings are discussed.