ABSTRACT
Peroxisomes are involved in various metabolic reactions. Rhizomelic chondrodysplasia punctata (RCDP) type 1 is one of the peroxisomal biogenesis disorders caused by mutations in the PEX7 gene and is inherited in an autosomal recessive manner. We present a nine-year-old boy with skeletal abnormalities and dysmorphic facial appearance. The patient was born to parents who were first cousins. Very-long-chain fatty acids and pristanic acid levels were in the normal range, but an elevated phytanic acid level was detected by gas chromatography/mass spectrometry. The PEX7 gene was sequenced in the patient and his parents. A novel homozygous mutation, c.192delT (p.F64Lfs*10), was identified in the patient and was present in heterozygosity in both parents. In conclusion, the clinical presentation and peroxisome profile of the patient suggest that this novel mutation leads to RCDP type 1.
Subject(s)
Chondrodysplasia Punctata, Rhizomelic/genetics , Mutation/genetics , Receptors, Cytoplasmic and Nuclear/genetics , Child , Chondrodysplasia Punctata, Rhizomelic/metabolism , Chondrodysplasia Punctata, Rhizomelic/pathology , Female , Gas Chromatography-Mass Spectrometry , Heterozygote , Homozygote , Humans , Male , Pedigree , Peroxisomal Targeting Signal 2 Receptor , Phytanic Acid/metabolism , Polymerase Chain ReactionABSTRACT
Primary fibroblasts established from embryos of NAD-dependent mitochondrial methylenetetrahydrofolate dehydrogenase-cyclohydrolase (NMDMC) knockout mice were spontaneously immortalized or transformed with SV40 Large T antigen. Mitotracker Red CMXRos staining of the cells indicates the presence of intact mitochondria with a membrane potential. The nmdmc(-/-) cells are auxotrophic for glycine, demonstrating that NMDMC is the only methylenetetrahydrofolate dehydrogenase normally expressed in the mitochondria of these cell lines. Growth of null mutant but not wild type cells on complete medium with dialyzed serum is stimulated about 2-fold by added formate or hypoxanthine. Radiolabeling experiments demonstrated a 3-10 x enhanced incorporation of radioactivity into DNA from formate relative to serine by nmdmc(-/-) cells. The generation of one-carbon units by mitochondria in nmdmc(-/-) cells is completely blocked, and the cytoplasmic folate pathways alone are insufficient for optimal purine synthesis. The results demonstrate a metabolic role for NMDMC in supporting purine biosynthesis. Despite the recognition of these metabolic defects in the mutant cell lines, the phenotype of nmdmc(-/-) embryos that begin to die at E13.5 is not improved when pregnant dams are given a glycine-rich diet or daily injections of sodium formate.
