Methylation Status of HPRT1 Promoter in HPRT Deficiency with Normal Coding Region

Abstract

Lesch-Nyhan syndrome is an X-linked recessive inborn error of metabolism due to a complete deficiency of hypoxanthine-guanine phosphoribosyltransferase (HPRT) activity (OMIM 300322). Partial deficiency of HPRT (OMIM 300323) is characterized by the effects of excess uric acid synthesis and a continuum spectrum of neurological manifestations, without the manifestations of full-blown Lesch-Nyhan syndrome. Both diseases have been associated with mutations in the HPRT1 gene. We have described one Lesch-Nyhan patient and four partial HPRT deficient patients with a normal HPRT1 coding region. These patients showed markedly decreased HPRT mRNA expression, but no mutation in their genomic regulatory sequences from HPRT1 gene. In this study, we analyzed the promoter region methylation status of the HPRT1 gene in these five HPRT deficient patients. Methods: DNA was bisulphite modified and a 620 bp fragment including 320 bp 5′ to start codon was amplified and sequenced. The methylation status of 35 CpG island 5′ to start codon and 28 CpG island 3′ to start codon were investigated in male controls, female controls, patients, and the patient's mothers. Primer pairs were designed for methylated-specific and unmethylated-specific amplification and PCR was performed employing DNA bisulphite treated as template. Results: No alterations in the methylation pattern of the HPRT1 promoter were found in the five HPRT deficient patients. Conclusions: The promoter region methylation status of these five HPRT deficient patients was similar to that of normal subjects. Thus, some other genetic alteration must explain a reduced enzyme activity with a normal gene coding region.