Lesch-Nyhan Disease (LND) is a rare X-linked genetic disease with hypoxanthine-guanine phosphoribosyltransferase (HGPRT) deficiency, due to mutation in the encoding gene, located on the X-chromosome. LND patients exhibit hyperuricemia with stones due to unrecycled purine accumulation and increased synthesis, and a devastating neurological syndrome with dystonia and self-injurious behaviour, choreoathetosis and spasticity. In spite of biochemical and molecular research, the fine connection between the neurological syndrome and HGPRT deficiency is still unclear, though there is consensus regarding brain neurotransmitter dysfunction with few dopaminergic neuron terminals in the striatum. The rarity of the disease makes it difficult to obtain homogeneous population of patients to study. The aim of this paper is to contribute to the understanding of the connection between genotype and phenotype in a cohort of Italian patients, to propose a reliable method of identifying carrier women in affected families, and to provide evidence of a possible link between HGPRT deficiency and altered adenosinergic and serotonergic neurotransmission. Biochemical and mutation analysis is reported in 28 LNS Italian patients from 25 families, with virtually no HGPRT activity and typical LNS phenotype. Genetic analysis identified 24 HPRT mutations, nine of which had never previously been reported, and no mutation hotspots. Carrier females were identified by a new semiquantitative real-time PCR. Studies performed by real-time PCR on knockout mice demonstrated altered adenosinergic and serotonergic pathways, with greatly increased ADORA1A receptor expression, slightly decreased ADORA2A expression and unchanged ADORA2B expression. Increased HTRC2 expression with no significant difference in mRNA editing suggested serotonergic involvement. The different approaches used allowed us to study certain aspects of LND, focusing on mutation analysis in patients and carriers and on simultaneous analysis of biochemical and genetic features. Mouse models elucidated the possible involvement of adenosine and serotonine receptors in the neurotransmission aberration occurring in HGPRT deficiency.