DNA-based diagnosis of isolated sulfite oxidase deficiency by denaturing high-performance liquid chromatography

Isolated sulfite oxidase deficiency is a rare autosomal recessive disease, characterized by severe neurological abnormalities, seizures, mental retardation, and dislocation of the ocular lenses, that often leads to death in infancy. There is a special demand for prenatal diagnosis, since no effective treatment is available for isolated sulfite oxidase deficiency. Until now, the cDNA sequence of the sulfite oxidase (SUOX) gene has been available, but the genomic sequence of the SUOX gene has not been published. In this study, we have performed a DNA-based diagnosis of isolated sulfite oxidase deficiency in a Chinese patient. To do so, we designed oligonucleotide primers for amplification of the predicted exons and intron-exon boundaries of the SUOX gene obtained from the completed draft version of the human genome. Using overlapping PCR products, we confirmed the flanking intronic sequences of the coding exons and that the entire 466-residue mature peptide is encoded by the last exon of the gene. We then performed mutation detection using denaturing high-performance liquid chromatography (DHPLC). The DHPLC chromatogram of exon 2b showed the presence of heteroduplex peaks only after mixing of the mutant DNA with the wild-type DNA, indicating the presence of a homozygous mutation. Direct DNA sequencing showed a homozygous base substitution at codon 160, changing the codon from CGG to CAG, which changes the amino acid from arginine to glutamine, i.e., R160Q. The DNA-based diagnosis of isolated sulfite oxidase deficiency will enable us to make an accurate determination of carrier status and to perform prenatal diagnosis of this disease. The availability of the genomic sequences of human genes from the completed draft human genome sequence will simplify the development of molecular genetic diagnoses of human diseases from peripheral blood DNA.