Autosomal recessive hypophosphatemic rickets (ARHR) is an extremely rare 
disorder of autosomal recessive inheritance, characterized by hypophosphatemia 
resulting from renal phosphate wasting. Dentin matrix protein 1 (DMP1), a 
noncollagenous extracellular protein, plays critical roles in bone 
mineralization and phosphate homeostasis. Recently, loss-of-function mutations 
in DMP1 gene have been identified as the molecular cause of ARHR. Here, we 
describe a Japanese family that includes two ARHR-affected siblings carrying a 
novel mutation of the DMP1 gene. The patients were a 53-year-old woman and a 
50-year-old man with short stature and skeletal deformities who were the 
offspring of a first-cousin marriage. Biochemical examination revealed 
hypophosphatemia with renal phosphate excretion and low levels of 1,25(OH)(2)D. 
Serum calcium, parathyroid hormone, and urinary calcium excretion were within 
the normal range, leading to clinical diagnosis of ARHR. Sequence analysis of 
peripheral leukocytes from the patients revealed that they carried a novel 
homozygous nonsense mutation in the DMP1 gene (98G>A, W33X), which leads to a 
truncated DMP protein with no putative biological function. Unaffected family 
members were heterozygous for the mutation. This is the first report of a 
Japanese family with ARHR carrying a novel mutation of the DMP1 gene.