GROWTH-PLATE ABNORMALITIES IN A NEW DWARF MOUSE MODEL - TICH

Growth plate cartilage calcification has been examined in a recently d escribed mouse mutant, tich, which is co-isogenic with the A.TL strain . Long bones were studied from 1-day old and 1-month-old mice which ca rried a homozygous recessive gene mutation making them short limbed an d dumpy. Specimens were studied by routine histology, scanning electro n microscopy and radiography. In 1-day-old tich mice the front of calc ified cartilage was recessed behind the advancing periosteum and bone. No similar recess was seen in control mice. At 1 month of age, a numb er of the long bone growth plates were irregularly thickened, particul arly in the central area. This produced a central tongue of non-calcif ied cartilage (particularly prominent in the proximal tibia) which gav e rise to a corresponding pit in the calcified cartilage layer, in mac erated specimens. This was accompanied by poor resorption of calcified cartilage. At both ages the presence of the respective defects was ra diographically confirmed. At present it is not known whether this is p rimarily a defect of calcification or resorption but its presence, app arently from a single mutation in a genetically defined mouse strain, makes it a potentially valuable model.