Molecular analysis of DMP1 mutants causing autosomal recessive hypophosphatemic rickets

Abstract

We previously demonstrated that the mutations Met1Val (M1V) and the deletion of nucleotides 1484-1490 (1484-1490del) in Dentin matrix protein-1 (DMP1) cause the novel disorder autosomal recessive hypophosphatemic rickets (ARHR), which is associated with elevated Fibroblast growth factor-23 (FGF23). To further understand the role of DMP1 in ARHR, we undertook molecular genetic and in vitro expression studies. First, we examined a kindred with a severe hypophosphatemic rickets phenotype and recessive inheritance. Analyses of this family demonstrated that the affected members had elevated serum FGF23 and carried a large, biallelic deletion that removed the majority of DMP1. At a minimum, this deletion encompassed 49 kb between DMP1 exon 3 and an intergenic region 5′ to the next telomeric gene, integrin-binding sialoprotein (IBSP). We next performed immunofluorescent studies in cells to understand the effects of the known ARHR mutations on DMP1 cellular processing. These analyses showed that the M1V DMP1 mutant was not sorted to the transGolgi network (TGN) and secretory pathway, but filled the entire cytoplasm. In contrast, the 1484-1490del mutant localized to the TGN and was secreted, similar to wild type DMP1. The 1484-1490del mutation replaces the DMP1 18 C-terminal amino acids with 33 non-native residues. Truncation of wild type DMP1 by these native 18 residues followed by Western blot and confocal microscopic analyses demonstrated a wild type expression pattern when compared with the 1484-1490del mutant, indicating that the last 18 residues are not critical for cellular trafficking, but that the 33 additional residues arising from the 1484-1490del mutation likely compromise DMP1 processing. The relationship between DMP1 and FGF23 is unclear. To test endogenous DMP1 response to serum metabolites that also regulate FGF23, UMR-106 cells were treated with 1,25 (OH) 2 vitamin D (1×10 −7 M) and showed a 12-fold increase in DMP1 mRNA and protein at 24 hr. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access Author ManuscriptBone. Author manuscript; available in PMC 2010 February 1. In summary, we have identified a novel DMP1 deletion as the cause of ARHR, as well as demonstrated that the ARHR mutations alter DMP1 cellular processing, and that DMP1 can be regulated by vitamin D. Taken together, this work expands our understanding of the genetic and molecular mechanisms associated with DMP1 alterations causing ARHR.

Amelogenesis Imperfecta and Other Biomineralization Defects in Fam20a and Fam20c Null Mice

“…All three of these lines show striking defects in dentin and rachitic changes in bone 27,119 accompanied by hypophosphatemia and elevated levels of FGF23. 26,54 Until now, mutations in only four genes (PHEX, FGF23, DMP1, and ENPP1) had been definitively linked to elevated levels of FGF23 and hypophosphatemic rickets. 55,79 Taken together, our findings strongly suggest that FAM20C should be considered an additional factor that influences biomineralization of dentin and bone by modulating levels of the phosphatonin FGF23.…”

Incidence and prevalence of nutritional and hereditary rickets in southern Denmark

“…All children with hereditary rickets are assumed to be referred to hospital and the observed incidence is therefore probably valid. Several authors have stated that hereditary rickets is now the most common cause of rickets in the western world (18)(19)(20)(21)(22)(23). In our study, hereditary rickets was the most common cause of rickets among ethnic Danish children, but among all children aged less than 3 years and living in southern Denmark, nutritional rickets was still the most common cause of rickets.…”

Striking Pathology Gold: A Singular Experience with Daily Reverberations: Sinonasal Hemangiopericytoma (Glomangiopericytoma) and Oncogenic Osteomalacia

“…Mice injected with cells that stably overexpress FGF23 develop a metabolic profile identical to patients with OO [46]. Serum FGF23 is elevated in disease states either through impaired degradation secondary to a missense mutation in autosomal dominant hypophosphatemic rickets or inactivating mutations impairing its degradation; ENPP1 (ecto-nucleotide pyrophsphatase/ phosphodiesterase-1) in Type 2 autosomal recessive hypophosphatemic rickets [51] PHEX (phosphate-regulating neutral endopeptidase) in x-linked hypophosphatemia, and DMP1 (dentin matrix-1) in Type 1 autosomal recessive hypophosphatemic rickets [52,53].…”

“…Overexpression of mineralization-related genes, such as matrix extracellular phosphoglycoprotein (MEPE), frizzled-related protein, DMP, and FGF7 have also been demonstrated in PMT [41,52,54,55]. It has been postulated that these proteins are responsible for the characteristic calcified matrix of PMTMCT, which subsequently recruits osteoblasts and provokes fibrohistiocytic and aneurysmal bone cyst-like reactions [18].…”