The molecular biology of Lesch-Nyhan syndrome

Mechanisms for phenotypic variation in Lesch-Nyhan disease and its variants

Lesch-Nyhan disease is a neurogenetic disorder caused by mutation of the HPRT1 gene on the X chromosome. There is significant variation in the clinical phenotype, with more than 300 different known mutations. There are few studies that have addressed whether similar mutations result in similar phenotypes across different patients because hypoxanthine-guanine phosphoribosyltransferase (HGprt) deficiency is rare, and most mutations are unique or limited to individual families. However, recent studies have revealed multiple unrelated patients with similar mutations, providing an opportunity to examine genotype-phenotype correlations. We found significant variation among the clinical features of 10 patients from 8 unrelated families all carrying a mutation replacing guanine with adenine at base position 143 (c.143G>A) in the HPRT1 gene. This mutation results in replacement of arginine by histidine at amino acid position 48 (p.arg48his) in the HGprt enzyme. Biochemically, the enzyme exhibits reduced thermal integrity, a mechanism that may explain clinical variation. The literature reveals similar clinical variation among other patients with similar mutations, although the variation is relatively minor across the whole population of patients. Identifiable sources of clinical variation include known limitations of clinical ascertainment and mechanisms that affect residual enzyme activity and stability. These results are helpful for understanding genotype-phenotype correlations and discordance and likely are applicable to other neurogenetic disorders where similar variation occurs.

Lesch-Nyhan syndrome: a study of motor behavior and cerebrospinal fluid neurotransmitters

We studied 5 boys, 2 to 10 years old, with marked or complete deficiency of hypoxanthine-guanine phosphoribosyltransferase and Lesch-Nyhan syndrome with varying degrees of mental retardation, dysarthria, chorea, dystonia, spasticity, and ataxia. Four patients had marked reduction of homovanillic acid in the cerebrospinal fluid (CSF) and all showed low CSF 3-methoxy-4-hydroxy phenylethylene glycol, indicating reduced dopamine and norepinephrine turnover. Three patients showed high CSF 5-hydroxyindoleacetic acid, suggesting increased serotonin turnover. Some patients improved with carbidopa-levodopa, but others benefited from tetrabenazine, a monoamine-depleting agent. This study provides support for the theory of abnormal central monoamine metabolism in Lesch-Nyhan syndrome.