Dopamine receptor upregulation in Lesch-Nyhan syndrome: a postmortem study

The brains of two patients with Lesch-Nyhan syndrome (LNS) were studied. The concentration of dopamine was decreased in the caudate nucleus of LNS patients. Immunohistochemical methods revealed that the dopamine (DA) D1 and D2 receptor and methionine-enkephalin immunoreactivities (IRs) were increased in the putamen, and less significantly in the caudate nucleus. The D1 and D2 receptor IRs of the cingulate cortex, the tryptophan-hydroxylase IR in the dorsal nucleus of the midbrain, as well as the substance P and methionine-enkephalin IRs of the nociception-conducting structures, including the periaqueductal gray and spinal trigeminal nucleus, were not changed. Tyrosine-hydroxylase IR was not decreased in the substantia nigra of the LNS patients. Therefore, the cause of the decreased dopaminergic activity in LNS may not be involved in the production of tyrosine hydroxylase in the substantia nigra. Developmental abnormalities due to the DA defect at an early age might exist in the postsynaptic structure in the striatum.

Bone marrow transplantation does not ameliorate the neurologic symptoms in mice deficient in hypoxanthine guanine phosphoribosyl transferase (HPRT)

The use of bone marrow transplantation (BMT) for the treatment of genetic diseases with neurologic involvement has yielded mixed results. We have employed a mouse model of Lesch-Nyhan disease (LND) to assess the efficacy of BMT in ameliorating the neurologic manifestations of the disease. Adult HPRT-deficient mice exhibit a measurable decrease in striatal dopamine levels and a hypersensitivity to amphetamine. Marrow-ablated adult HPRT-deficient mice were transplanted with marrow from congenic HPRT-expressing mice. BMT altered neither the neurochemical nor the behavioral phenotypes in either HPRT-positive or HPRT-deficient mice. Barring any important species differences, these results suggest that BMT in its present form may not be an effective therapy for Lesch-Nyhan syndrome.

Influence of age and strain on striatal dopamine loss in a genetic mouse model of Lesch-Nyhan disease

Lesch-Nyhan disease is a neurogenetic disorder caused by deficiency of the purine salvage enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT). Affected individuals exhibit a characteristic pattern of neurological and behavioral features attributable in part to dysfunction of basal ganglia dopamine systems. In the current studies, striatal dopamine loss was investigated in five different HPRT-deficient strains of mice carrying one of two different HPRT gene mutations. Caudoputamen dopamine concentrations were significantly reduced in all five of the strains, with deficits ranging from 50.7 to 61.1%. Mesolimbic dopamine was significantly reduced in only three of the five strains, with a range of 31.6-38.6%. The reduction of caudoputamen dopamine was age dependent, emerging between 4 and 12 weeks of age. Tyrosine hydroxylase and aromatic amino acid decarboxylase, two enzymes responsible for the synthesis of dopamine, were reduced by 22.4-37.3 and 22.2-43.1%, respectively. These results demonstrate that HPRT deficiency is strongly associated with a loss of basal ganglia dopamine. The magnitude of dopamine loss measurable is dependent on the genetic background of the mouse strain used, the basal ganglia subregion examined, and the age of the animals at assessment.

Purine metabolism in female heterozygotes for hypoxanthine-guanine phosphoribosyltransferase deficiency

BACKGROUND

Female carriers of the X-linked recessive disorder hypoxanthine-guanine phosphoribosyltransferase (HPRT) deficiency show somatic cell mosaicism, and this may cause an increased synthesis of purines. We have examined whether urinary oxypurines could be useful for carrier diagnosis.

METHODS

Carrier testing was performed in 35 women belonging to 16 unrelated Spanish families with at least one subject affected by the Lesch-Nyhan syndrome (11 families, 14 patients) or the Kelley-Seegmiller syndrome (five families, six patients) by means of HPRT and adenine phosphoribosyltransferase activities in hair follicles and/or molecular studies. Plasma and 24-h urinary concentrations of hypoxanthine, xanthine and uric acid were measured while subjects were on a purine-restricted diet.

RESULTS

Mean plasma urate concentrations and 24-h urinary hypoxanthine, xanthine and uric acid excretion rates were significantly higher in 22 heterozygotes than in 13 non-carriers (P < 0.02). Daily urinary oxypurine excretion rates were also significantly higher in heterozygotes than in 12 normal women (P = 0.0011). Cumulative 5-day radioactivity excretion after [8-14C]-adenine infusion was markedly increased in 10 carrier women compared with five normal women (P = 0.0369). The sensitivity of 24-h urinary hypoxanthine and xanthine excretion rates was 86% and 77%, respectively, and the specificity 100% for both tests.

CONCLUSION

Female heterozygotes for HPRT deficiency show an enhanced purine nucleotide degradation and purine overproduction. An elevated hypoxanthine and/or xanthine excretion rate differentiated most heterozygotes for HPRT deficiency from non-carrier women and thus could be useful for carrier diagnosis.

Proton MR spectroscopy in Lesch-Nyhan disease

In vivo proton spectra for four patients with Lesch-Nyhan disease and four control subjects matched for age and sex were acquired from voxels (1.5 x 1.5 x 1.5 cm3) placed in the prefrontal cortex and striatum. The patients with Lesch-Nyhan disease had decreased metabolites, especially N-acetylaspartate and glutamate/glutamine, only in the prefrontal cortex as compared with the control group. These findings suggest axonal loss in the prefrontal area of this population. The cortical glutamate/glutamine peak decrement does not confirm cytopathologic studies of Lesch-Nyhan disease and deserves further investigation.

Cross-sensitization between footshock stress and apomorphine on self-injurious behavior and neostriatal catecholamines in a rat model of Lesch-Nyhan syndrome

The effects of footshock sensitization (priming), apomorphine (APO) priming and their combination on behavior and neostriatal and cortical catecholamines were examined in adult rats which had neonatally received bilateral intracerebroventricular injections with 6-hydroxydopamine (6-OHDA; a model of Lesch-Nyhan syndrome (LNS)) or vehicle (unlesioned rats). Lesioned (6-OHDA-treated) rats displayed self-biting (SB; 7/20 rats) and self-injurious behavior (SIB; 1/20 rats) during APO priming, but not during footshock priming. During subsequent acute cumulative APO dosing, 20-30% of lesioned rats primed with APO alone or footshock alone displayed SB and SIB. However, SB and SIB incidence in APO+footshock-primed lesioned rats was nearly tripled. Dopamine (DA) synthesis, metabolism and extracellular concentrations (disposition) in unlesioned rats and in cortices of lesioned animals were unaffected by priming. In lesioned rats primed with APO alone or footshock alone, only neostriatal 3-methoxytyramine (3-MT) was significantly increased. However, neostriatal DA and metabolite concentrations (and norepinephrine (NE)) were all significantly elevated in lesioned rats primed with both APO and footshock. These results confirm that neonatal 6-OHDA-induced neostriatal catecholamine depletion can be antagonized by experiential change, suggest that behavioral and neurochemical cross-sensitization between APO and footshock in such rats is unidirectional and support the view that stress can exacerbate the incidence of SIB in LNS.

Analysis of abnormalities in purine metabolism leading to gout and to neurological dysfunctions in man

A modelling approach is used to analyse diseases associated with purine metabolism in man. The specific focus is on deficiencies in two enzymes, hypoxanthine:guanine phosphoribosyltransferase and adenylosuccinate lyase. These deficiencies can lead to a number of symptoms, including neurological dysfunctions and mental retardation. Although the biochemical mechanisms of dysfunctions associated with adenylosuccinate lyase deficiency are not completely understood, there is at least general agreement in the literature about possible causes. Simulations with our model confirm that accumulation of the two substrates of the enzyme can lead to significant biochemical imbalance. In hypoxanthine:guanine phosphoribosyltransferase deficiency the biochemical mechanisms associated with neurological dysfunctions are less clear. Model analyses support some old hypotheses but also suggest new indicators for possible causes of neurological dysfunctions associated with this deficiency. Hypoxanthine:guanine phosphoribosyltransferase deficiency is known to cause hyperuricaemia and gout. We compare the relative importance of this deficiency with other known causes of gout in humans. The analysis suggests that defects in the excretion of uric acid are more consequential than defects in uric acid synthesis such as hypoxanthine:guanine phosphoribosyltransferase deficiency.

The recognition of Lesch-Nyhan syndrome as an inborn error of purine metabolism

Lesch-Nyhan syndrome was first described over thirty years ago. The original patient was a 4-year-old boy with neurological abnormalities as well as haematuria. Crystals in his urine were identified and confirmed to be uric acid. The massive excretion of this purine led to metabolic studies using isotopically labelled uric acid to study turnover rates. Clues to the site of the enzyme defect resulted from studies with the immunosuppressive agent azathioprine, which normally causes uric acid concentrations to fall in blood and urine but was without effect in a Lesch-Nyhan patient. A deficiency of hypoxanthine phosphoribosyltransferase (HPRT) activity explained this observation in Lesch-Nyhan patients. Subsequent studies have indicated that the degree of HPRT deficiency appears to determine the severity of the disease. Molecular studies have shown that most families carry a unique mutation. Attempts are being made to correlate the type and site of a specific mutation with a particular phenotype.

Mice with adenine phosphoribosyltransferase deficiency develop fatal 2,8-dihydroxyadenine lithiasis

Deficiencies in different steps of purine metabolism give rise to a number of human inherited disorders. Lesch-Nyhan syndrome is a severe neurological disorder, caused by a deficiency in the purine salvage enzyme hypoxanthine phosphoribosyltransferase (HPRT). HPRT-deficient mice have been generated, but have proved to be an unsuccessful model of the human disease. We have suggested that this may be due to a greater dependency in rodents on the other purine salvage enzyme, adenine phosphoribosyltransferase (APRT). We have generated an APRT-deficient mouse line by gene targeting, with a phenotype that closely resembled the symptoms of APRT deficiency in man. APRT null mice were viable, but 90% died prematurely before 6 months of age, displaying highly abnormal kidney morphology, with pathology characteristic of tubule obstruction. These mice have elevated urinary levels of adenine and 2,8-dihydroxyadenine, a highly insoluble adenine derivative, plus birefringent crystalline deposits and calculi within tubules throughout the kidney. A standard therapy for APRT-deficient human patients is the administration of the xanthine oxidase inhibitor, allopurinol. This has proved an effective therapy for APRT null mice, preventing accumulation of 2,8-dihydroxyadenine and much of the resultant renal obstruction, allowing us to establish a breeding line. We believe that these mice should provide a useful model for further study of APRT deficiency in humans. Furthermore, by generating APRT and HPRT double mutants, we will be able to test our hypothesis that both genes must be inactivated in mice before a model for Lesch-Nyhan syndrome can be obtained.

Dopamine transporters are markedly reduced in Lesch-Nyhan disease in vivo

Dopamine (DA) deficiency has been implicated in Lesch-Nyhan disease (LND), a genetic disorder that is characterized by hyperuricemia, choreoathetosis, dystonia, and compulsive self-injury. To establish that DA deficiency is present in LND, the ligand WIN-35,428, which binds to DA transporters, was used to estimate the density of DA-containing neurons in the caudate and putamen of six patients with classic LND. Comparisons were made with 10 control subjects and 3 patients with Rett syndrome. Three methods were used to quantify the binding of the DA transporter so that its density could be estimated by a single dynamic positron emission tomography study. These approaches included the caudate- or putamen-to-cerebellum ratio of ligand at 80-90 min postinjection, kinetic analysis of the binding potential [Bmax/(Kd x Vd)] using the assumption of equal partition coefficients in the striatum and the cerebellum, and graphical analysis of the binding potential. Depending on the method of analysis, a 50-63% reduction of the binding to DA transporters in the caudate, and a 64-75% reduction in the putamen of the LND patients was observed compared to the normal control group. When LND patients were compared to Rett syndrome patients, similar reductions were found in the caudate (53-61%) and putamen (67-72%) in LND patients. Transporter binding in Rett syndrome patients was not significantly different from the normal controls. Finally, volumetric magnetic resonance imaging studies detected a 30% reduction in the caudate volume of LND patients. To ensure that a reduction in the caudate volume would not confound the results, a rigorous partial volume correction of the caudate time activity curve was performed. This correction resulted in an even greater decrease in the caudate-cerebellar ratio in LND patients when contrasted to controls. To our knowledge, these findings provide the first in vivo documentation of a dopaminergic reduction in LND and illustrate the role of positron emission tomography imaging in investigating neurodevelopmental disorders.

FR discrimination training reverses 6-hydroxydopamine-induced striatal dopamine depletion in a rat model of Lesch-Nyhan syndrome

Five-day-old rats received 6-hydroxydopamine (6-HD; 100 micrograms base) or vehicle intracisternally. Striatal and cortical dopamine (DA) and metabolite levels were then determined when animals were three or 8.5 months of age and the latter rats had been weight-reduced for 5.5 months. In the latter animals these determinations were made 1 month following 4.5 months of home-cage confinement (untrained animals) or of food-maintained fixed-ratio (FR) discrimination training involving either a single discrimination (performance animals) or incrementally more difficult discriminations. Striatal DA levels in 3-month-old and 8.5-month-old (untrained) 6-HD-treated rats were, respectively, only 3% and 11% of those in untrained vehicle-treated animals (controls). Despite such large depletions, striatal DA levels in 6-HD-treated performance rats were 3-fold higher than those in untrained age-matched 6-HD-treated rats (i.e., were 32% of values in controls) while those in incrementally trained 6-HD-treated animals were even higher (i.e., were 60% of control values). Related changes occurred in levels of most metabolites. However, in incrementally trained rats, striatal 3-methoxytyramine concentrations were 154% of control values. Cortical DA and metabolite levels were little affected by 6-HD treatment. The present results confirm and extend our earlier observations suggesting that reversal of 'irreversible' neonatal 6-HD-induced striatal dopamine and metabolic depletion can be accomplished by environmental (training) manipulations in adult rats.

Lesch-Nyhan syndrome and its pathogenesis: normal nicotinamide-adenine dinucleotide but reduced ATP concentrations that correlate with reduced poly(ADP-ribose) synthetase activity in HPRT-deficient lymphoblasts

In hypoxanthine (guanine) phosphoribosyltransferase- (HPRT; EC 2.4.2.8) deficient lymphoblasts, ATP but not nicotinamide-adenine dinucleotide coenzyme concentrations are reduced by limited nutrition. Such reduced ATP concentrations are correlated with reduced poly(ADP-ribose) synthetase (polyADPRT; EC 2.4.2.30) activity; this reduces the breakdown of nicotinamide-adenine dinucleotide coenzymes and thus explains their normal intracellular concentrations. Since reductions in poly(ADP-ribose) synthetase activity reduce DNA repair, alterations in DNA could accumulate even in non-multiplying cells such as neurons, especially in the continuously active 'respiratory centre'. Our Lesch-Nyhan patients suffered respiratory deaths between 15 and 20 years of age.

Ultrastructure of Met5-enkephalin terminals in the caudate-putamen nuclei of adult rats receiving neonatal intranigral 6-hydroxydopamine

Destruction of dopamine neurons of the nigrostriatal pathway in the early postnatal rat enhances the levels of Met5-enkephalin in the adult dorsal striatum (caudate-putamen nuclei) and may contribute to the abnormal self-injurious behavior seen in humans with Lesch-Nyhan disease. We examined whether there were ultrastructural changes in Met5-enkephalin immunoreactive terminals in the rat model that might reflect cellular sites for enhanced activity of these opioid neurons. At 3 days postnatal, 10-20 nl injections of a 1% solution of the dopamine neurotoxin, 6-hydroxydopamine (6-OHDA), or vehicle were placed unilaterally in the region of the substantia nigra of 25 litters of male rat pups. In adulthood (72-80 days postnatal), the brains of these animals were fixed by vascular perfusion with an aldehyde solution. Met5-enkephalin immunolabeling was examined in coronal sections at three rostrocaudal levels through the caudate-putamen nuclei of control (ipsilateral and contralateral to vehicle and contralateral to 6-OHDA) and experimental (ipsilateral to 6-OHDA) groups. In selectively lesioned animals, there was a significant increase in the relative optical density of immunoautoradiographic labeling for enkephalin throughout the rostrocaudal striatum ipsilateral to 6-OHDA as compared to control groups. Electron microscopy revealed immunoperoxidase labeling for enkephalin in axon terminals and more rarely in soma and dendrites irrespective of drug treatment. In both experimental and control striatal tissues, the enkephalin immunoreactive terminals formed primarily symmetric synapses with unlabeled dendrites or spines. However, ipsilateral to 6-OHDA injections there was a small (5.4%), but significant increase in the proportion of enkephalin immunoreactive terminals contacting dendritic spines, the known targets of dopamine terminals. Appositions were commonly detected between enkephalin immunoreactive terminals and other morphologically heterogeneous axons in the striatum ipsilateral to 6-OHDA and in control tissues. Met5-enkephalin immunoreactive terminals in adult striatum ipsilateral to 6-OHDA injections showed a 214% increase in volume as compared to vehicle-injected controls. Concurrently, there was a small (13%), but significant increase in the numerical density (number/volume) of enkephalin-labeled terminals both contralateral and ipsilateral to 6-OHDA injections. These results suggest that a change in bouton size is the major mechanism by which striatal enkephalin neurons alter their synaptic efficacy and target associations to compensate for damage to the nigrostriatal dopamine neurons.

[Clinical spectrum of hypoxanthine-guanine phosphoribosyltransferase deficiency: study of 12 cases]

BACKGROUND

The hypoxanthine-guanine phosphoribosyltransferase deficiency (HGPRT) may have two clinical forms: that of the Lesch-Nyhan syndrome (complete HGPRT deficiency) and that of the Kelley-Seegmiller syndrome (partial HGPRT deficiency). The clinical and biochemical features of the HGPRT deficiency are not completely known.

METHODS

A series of 12 patients, 8 with the Lesch-Nyhan syndrome and 4 with the Kelley-Seegmiller syndrome are described. The plasma and urine concentrations of hypoxanthine, xanthine and uric acid were compared with those obtained in 20 normal subjects and 41 patients with primary gout. The molecular defect which determines the deficient HGPRT activity was studied in one patient with the Kelley-Seegmiller syndrome.

RESULTS

The 8 patients with the Lesch-Nyhan syndrome presented choreoathetosis, corticospinal motor system dysfunction, mental retardation and signs of self mutilation. The neurologic manifestations of the patients with the Kelley-Seegmiller syndrome were very heterogeneous: two patients had psychomotor retardation with spastic movement, one was mentally retarded with generalized dystonia and one patient only had gout with no neurologic manifestations. The erythrocytic HGPRT activity ranged between 0.28 and < 0.01 nmol/h and mg of hemoglobin in all the patients. Plasma and urine purine concentrations were very high, being greater than those in normal subjects and patients with gout (p < 0.01). A mutation was identified in exon 3 (substitution of guanine with thymine) conditioning the substitution of the normal glycine amino acid by valine (HGPRT Madrid) on molecular study.

CONCLUSIONS

The hypoxanthine-guanine phosphoribosyltransferase deficiency has a heterogeneous clinical expression. The activity of this enzyme in erythrocytes and the results of the metabolism of the purines do not allow prediction of the severity of the clinical manifestations.

Dopamine deficiency in a genetic mouse model of Lesch-Nyhan disease

We have examined several aspects of neurotransmitter function in the brains of mice carrying a deletion mutation in the gene encoding the purine salvage enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT). During the first 6 weeks of postnatal development, dopamine levels in whole-brain extracts from the mutant mice (HPRT-) failed to increase at rates comparable to normal animals, resulting in 40% lower dopamine levels throughout adulthood. Regional analysis in adult animals showed the caudoputamen to be the most severely affected region, with dopamine deficits of 48-64%. Dopamine levels in other regions were normal or less severely affected. The decrease in dopamine was accompanied by a decrease in tyrosine hydroxylase (TH) activity, the rate-limiting step in dopamine synthesis. Kinetic analysis of TH extracted from the caudoputamen of normal and HPRT- mice demonstrated a 45% decrease in Vmax with an increased affinity for the tetrahydropterin cofactor in the mutants. Labeling of midbrain dopamine neurons using TH immunohistochemistry revealed no obvious deficits in the number of midbrain dopamine neurons, but quantitative autoradiographic studies revealed significant reductions in the binding of 3H-N-[1-(2-benzo(beta)thiophenyl)cyclohexyl]piperidine (3H-BTCP) to dopamine uptake sites in the forebrain of the mutants. In contrast to these abnormalities of the dopamine systems in the mutant mice, other neurotransmitter systems appeared relatively unaffected. Norepinephrine, 5-HT, tryptophan hydroxylase, and glutamic acid decarboxylase were present at normal levels in the brains of the mutants. ChAT activity was slightly lower than normal in the caudoputamen of the mutant animals, but was normal in all other brain regions examined. These results indicate that HPRT deficiency is associated with a relatively specific deficit in basal ganglia dopamine systems that emerges during the first 2 months of postnatal development.

Characterization of the alterations in purine nucleotide metabolism in hypoxanthine-guanine phosphoribosyltransferase-deficient rat neuroma cell line

A rat neuroma cell line (B103 4C), deficient of hypoxanthine-guanine phosphoribosyltransferase (HGPRT), was utilized as a model tissue in search for the biochemical basis of the Lesch-Nyhan syndrome (LNS). The HGPRT-deficient neurons exhibited the following properties: an almost complete absence of uptake of guanine and of hypoxanthine into intact cell nucleotides (0.92% and 0.69% of normal, respectively); a significant increase in the availability of 5'-phosphoribosyl-1-pyrophosphate; a three- to fourfold acceleration of the rate of de novo nucleotide synthesis; a normal excretion of xanthine, but 15-fold increase in the excretion of hypoxanthine into the culture media; a normal cellular purine nucleotide content, including the absence of 5-amino-4-imidazole carboxamide nucleotides (Z-nucleotides), but enhanced turnover of adenine nucleotides (loss of 86% of the radioactivity of the prelabeled pool in 24 h, in comparison to 73% in the normal line), and an elevated UTP content. The results suggest that, under physiological conditions, guanine salvage does not occur in the normal neurons, but that hypoxanthine salvage is of great importance in the homeostasis of the adenine nucleotide pool. The finding of the normal profile of purine nucleotides in the HGPRT-deficient neurons indicates that the lack of hypoxanthine salvage is adequately compensated by the enhanced de novo nucleotide synthesis. These results did not furnish evidence in support of the possibility that GTP or ATP depletion, or Z-nucleotide accumulation, occurs in HGPRT-deficient neurons and that these are etiological factors causing the neurological abnormalities in LNS.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain purines in a genetic mouse model of Lesch-Nyhan disease

Mice carrying a mutation in the gene encoding the purine salvage enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT) have recently been produced to provide an animal model for Lesch-Nyhan disease. The current studies were conducted to characterize the consequences of the mutation on the expression of HPRT and to characterize potential changes in brain purine content in these mutants. Our results indicate that the mutant animals have no detectable HPRT-immunoreactive material on western blots and no detectable HPRT enzyme activity in brain tissue homogenates, confirming that they are completely HPRT deficient (HPRT-). Despite the absence of HPRT-mediated purine salvage, the animals have apparently normal brain purine content. However, de novo purine synthesis, as measured by [14C]formate incorporation into brain purines, is accelerated four- to fivefold in the mutant animals. This increase in the synthesis of purines may protect the HPRT- mice from potential depletion of brain purines despite complete impairment of HPRT-mediated purine salvage.

Functional analysis of brain dopamine systems in a genetic mouse model of Lesch-Nyhan syndrome

The Lesch-Nyhan syndrome is a neurogenetic disorder caused by congenital deficiency of the purine salvage enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT). The disorder is characterized by prominent neurobehavioral abnormalities which appear to result in part from dysfunction of striatal dopamine systems. HPRT-deficient (HPRT-) mutant strains of mice have been produced as animal models for this syndrome, but these animals exhibit none of the neurobehavioral abnormalities seen in Lesch-Nyhan patients. The present studies describe the behavioral responses of three strains of mice carrying one of two mutations in the HPRT gene to agents which interact with brain dopamine systems. HPRT- mice are more sensitive than age- and sex-matched littermates to the motor-activating properties of dopamine-releasing agents (amphetamine, amfonelic acid and methylphenidate), but not dopamine uptake inhibitors (GBR 12909 and nomifensine). The enhanced sensitivity of the HPRT- mice to the dopamine-releasing agents is not caused by dopamine receptor supersensitivity, because the HPRT- mice do not show enhanced motor responses to the direct D1/D2 dopamine receptor agonist apomorphine or to the selective D1 dopamine receptor agonist SKF 38393. The function of regulatory dopamine autoreceptors, as assessed by suppression of spontaneous motor activity by low doses of R(-)-propylnorapomorphine, also appears normal in the HPRT- mice. Biochemical analysis shows that the HPRT- mice have significantly lower levels of dopamine (-45%), but normal levels of tyrosine, 3,4-dihydroxyphenylacetic acid, homovanillic acid and 3-methoxytyramine in the caudoputamen. In contrast to the deficit in caudoputamen dopamine, no deficits were noted in the accumbens of the HPRT- mice. These results indicate the existence of an inherent abnormality in the dopamine systems in the brains of HPRT- mice, despite their apparently normal spontaneous behavior.

Serotonin-GABA treatment is hypothesized for self-injury in Lesch-Nyhan syndrome

The self-injurious movements of Lesch-Nyhan patients are considered extremely severe and currently intractable. Lesch-Nyhan syndrome is a genetic disorder of purine metabolism resulting in several abnormalities, one of which is elevated levels of xanthine. The author reasons that elevated plasma xanthine sets off a chain of events that produce excessive endogenous convulsants and diminished endogenous anticonvulsants. Treatment is proposed for self-injury in Lesch-Nyhan that entails reducing production of two endogenous convulsants (kynurenine and quinolinic acid) and enhancing two endogenous anticonvulsants (serotonin and gamma aminobutyric acid).