tiptoe-walking [mouse model](English)

• a naturally occurring mutant which exhibits ossification of the spinal ligaments very similar to human OPLL. Using a positional candidate-gene approach, we determined the ttw phenotype is caused by a nonsense mutation (glycine 568 to stop) in the Npps gene which encodes nucleotide pyrophosphatase. This enzyme regulates soft-tissue calcification and bone mineralization by producing inorganic pyrophosphate, a major inhibitor of calcification. The accelerated bone formation characteristic of ttw mice is likely to result from dysfunction of NPPS caused by predicted truncation of the gene product, resulting in the loss of more than one-third of the native protein; previously designated twy
• NPPS, OPLL
• Experimental animal, Model(ing), Spine (or spinal cord)
• https://doi.org/10.1038/956