Skeletal growth and development of achondroplastic mice

Skeletal development of achondroplastic (cn/cn) mice, aged 2 to 7 weeks, was investigated and compared with that of equally old non-achondroplastic sibs. Differences in body weight and dry weight of femora, tibiae, humeri, and unlae, and in the length of tibiae, unlae, and humeri became more marked with advancing age. Of the biochemical assays carried out, only those for sialic acid and hydroxyproline disclosed significant differences between dwarfs and non-dwarfs, all dwarfs having higher levels of hydroxyproline, and most of them having higher sialic acid levels than the non-dwarfs. Histologically, no distinction could be made between growth zones of non-dwarfs, of cn/+, or +/+ genotype. Among the dwarfs, two groups differing as to the severity of the skeletal abnormality could be distinguished. The differences between dwarfs were most marked in the growth zones of tibiae and femora, less conspicuous in those of vertebrae and least pronounced at the chondro-osseous junction of the ribs. The cause or causes of the histologic heterogeneity remain unknown.