Abnormal development of hypoxanthine-guanine phosphoribosyltransferase-deficient CNS neuroblastoma.

Lesch-Nyhan syndrome encompasses a host of neurological symptoms, caused by a deficiency of the purine salvage enzyme, hypoxanthine-guanine phosphoribosyltransferase (HGPRT). How the absence of this enzymes activity affects development of the nervous system is unknown. In this study, we examined the ability of N2aTG, a HGPRT-deficient neuroblastoma and its HGPRT-positive counterpart to proliferate and differentiate at various densities. In summary, N2aTG cells proliferated less and differentiated more than N2a cells, with the former cells exhibiting enhanced sensitivity to the effects of low-density culture. Given the homogeneity of this neuroblastoma cell line and its use in studies of neuronal development, the present study indicates that N2aTG cells may prove a suitable in vitro model for the study of non-dopaminergic neuronal development in Lesch-Nyhan syndrome.     

Elevated UTP and CTP content in cultured neurons from HPRT-deficient transgenic mice

Hypoxanthine-guanine phosphoribosyltransferase (EC 2.4.2.8.; HPRT) catalyzes the salvage synthesis of inosine-5′-monophosphate (IMP) and guanosine-5′-monophosphate (GMP) from the purine bases hypoxanthine and guanine, respectively. Complete deficiency of HPRT activity is associated with the Lesch-Nyhan syndrome (LNS), characterized by excessive purine production and severe neurological manifestations. The etiology of the metabolic consequences of HPRT deficiency is clarified, but that of the neurological manifestations is not yet understood. HPRT-deficient mice represent an experimental animal model of LNS. In search for a possible metabolic abnormality in LNS brains, connecting the neurological deficit to HPRT deficiency, the purine and pyrimidine nucleotide content of cultured neurons, prepared from HPRT-deficient transgenic mice, was now determined. The HPRT-deficient neuronal cultures exhibited a significantly elevated content of the pyrimidine nucleotides UTP (1.33-fold the normal level, p=0.0002) and CTP (1.28-fold the normal level, p=0.02), but normal content of the purine nucleotides ATP and GTP. This abnormality in neuronal pyrimidine nucleotide content may be associated with the pathophysiology of the neurological deficit in LNS.     

The biochemical basis of the behavioral disorder in the Lesch-Nyhan syndrome

An inherited complete deficiency of hypoxanthine-guanine phosphoribosyltransferase in male children is associated with a severe neurological disorder characterized by chloroform and athetoid movements, hypertonicity, mental retardation, and self-injurious behavior. In the review that follows several possible mechanisms by which the enzyme defect may cause the CNS disorder are discussed. Current evidence suggests that the primary neural deficit in the Lesch-Nyhan syndrome is a deficiency of dopamine in the basal ganglia. It is argued that this neurochemical lesion results from a deficiency of purine nucleotides which impairs arborization of nigrostriatal neurons during perinatal development. Differences in the ontogenetic timing of the neurochemical lesion may be partly responsible for the different neurological symptoms displayed by persons afflicted with the Lesch-Nyhan and Parkinson's syndromes.     

Recurrent coma and Lesch-Nyhan syndrome.

A patient with Lesch-Nyhan syndrome has had 3 recurrent episodes of coma, each associated with an acute illness. Extensive investigation for known causes of coma has failed to yield a diagnosis. Although coma is not generally recognized as a feature of Lesch-Nyhan syndrome, similar patients have been reported previously. This and other episodic phenomena observed in Lesch-Nyhan syndrome may be explained by the disruption of cellular energy metabolism due to purine depletion, consequent to lack of the purine salvage pathway normally provided by the hypoxanthine-guanine-phosphoribosyl-transferase enzyme.     

Animal models of Lesch-Nyhan syndrome

In humans, deficiency of the enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT) is associated with a disorder known as Lesch-Nyhan syndrome which includes severe neurobehavioral abnormalities. Several animal models which have been developed to examine the neurobiologic substrates of this disorder have suggested a role for abnormal function in purine/dopamine neurotransmission, but the relationship between HPRT-deficiency and these abnormalities remains unknown. Recently, HPRT-deficient mice have been produced which appear to have similar, though more subtle changes in brain dopamine function. These mice will be useful in elucidating the relationship between HPRT-deficiency and the neurological deficits observed in patients with this disorder.     

Gilles de la Tourette syndrome: further studies and thoughts.

A possible association between the Gilles de la Tourette and Lesch-Nyhan syndromes has recently been postulated. Fourteen patients with Tourette syndrome demonstrated no similarity to Lesch-Nyhan based upon patterns of inheritance, behavioral changes, or alterations of purine metabolism. Despite a strong male predominance, a sex-linked pattern of inheritance could not be confirmed. Self-mutilating behavior was found in 4 male patients but was readily differentiated from that characteristic of the Lesch-Nyhan syndrome. Quantitation of hypoxanthine-guanine phosphoribosyltransferase and isoelectric focusing of its isoenzymes produced results that were indistinguishable from those in controls. We speculate that, pathophysiologically, Tourette syndrome represents an imbalance between the central neurotransmitters dopamine and serotonin rather than an alteration in purine metabolism.     

Hypoxanthine guanine phosphoribosyltransferase (HGPRT) in Gilles de la Tourette syndrome.

Hypoxanthine guanine phosphoribosyltransferase (HGPRT) and adenosine phosphoribosyltransferase (APRT) were examined from 11 individuals with Gilles de la Tourette syndrome, 10 of their first- or second-degree relatives, and 3 normal controls. It has been suggested that in some self-mutilating Tourette patients, HGPRT shows a time-related loss of activity at 4 degrees C, and an unusual isoelectrofocusing pattern. Although 3 patients experienced self-mutilation, no consistent abnormalities were found in the temperature-stability of their HGPRT at 4 degrees C and 70 degrees C, or in isoelectrofocusing of HGPRT purified by immunoprecipitation. An alteration of the purine metabolic pathway in Tourette syndrome has not been established.     

Abnormal development of hypoxanthine–guanine phosphoribosyltransferase-deficient CNS neuroblastoma

Lesch–Nyhan syndrome encompasses a host of neurological symptoms, caused by a deficiency of the purine salvage enzyme, hypoxanthine–guanine phosphoribosyltransferase (HGPRT). How the absence of this enzymes activity affects development of the nervous system is unknown. In this study, we examined the ability of N2aTG, a HGPRT-deficient neuroblastoma and its HGPRT-positive counterpart to proliferate and differentiate at various densities. In summary, N2aTG cells proliferated less and differentiated more than N2a cells, with the former cells exhibiting enhanced sensitivity to the effects of low-density culture. Given the homogeneity of this neuroblastoma cell line and its use in studies of neuronal development, the present study indicates that N2aTG cells may prove a suitable in vitro model for the study of non-dopaminergic neuronal development in Lesch–Nyhan syndrome.     

New mutations of the HPRT gene in Lesch-Nyhan syndrome

Lesch-Nyhan syndrome is an X-linked recessive disorder involving the purine metabolism, with resultant hyperuricemia, choreoathetosis, self-mutilation, and profound neurologic dysfunction. A deficiency of the enzyme hypoxanthine guanine phosphoribosyl-transferase is responsible for the disease. The human HPRT gene is located at Xq26-27 and consists of 57 base pairs. At least 2,000 mutations throughout the HPRT gene coding region from exon 1-9 have been reported. Four patients from three Chinese families were diagnosed with Lesch-Nyhan syndrome according to the clinical and laboratory findings. DNA studies revealed the first family (Patients 1 and 2) had a missense mutation in exon 3 of the HPRT encoding region. This novel mutation occurs in the hot spot of the HPRT gene. The second family (Patient 3) was found to have a missense mutation in exon 8 of the HPRT gene. The third family (Patient 4) carried a mutation in the splicing region of intron 4 of the HPRT gene. All three mutations were de novo.     

A dopamine deficiency model of Lesch-Nyhan disease--the neonatal-6-OHDA-lesioned rat

Lesch-Nyhan syndrome is characterized by a deficiency of the enzyme hypoxanthine phosphoribosyl transferase (HPRT), compulsive self-mutilatory behavior (SMB), and a loss of central dopaminergic neurons. In order to model the loss of central dopamine-containing neurons in this developmental disorder, neonatal rat pups 3 days of age were given the neurotoxin 6-OHDA intracisternally to reduce brain dopamine. Accompanying the profound loss of dopamine produced by this treatment was an increase in striatal serotonin content. When these neonatally lesioned rats were challenged as adults with systemically administered L-DOPA or with muscimol administration into substantia nigra reticulata (SNR), SMB was observed, a response not observed in unlesioned rats. Thus, the neonatally lesioned rats exhibit increased susceptibility for SMB. Since a D1-dopamine antagonist blocked the SMB response to L-DOPA, it was proposed that D1-dopamine receptors were critical to this behavioral response. Basic investigations concerning D1-dopamine receptor mechanisms in the lesioned rats have been performed and these are reviewed. The data in the neonatally lesioned rats provide convincing evidence that the absence of central dopaminergic neurons is responsible for at least some of the neurological symptoms of the Lesch-Nyhan syndrome, a finding consistent with data collected in mice with an HPRT deficiency.     

Impaired differentiation of HPRT-deficient dopaminergic neurons: A possible mechanism underlying neuronal dysfunction in Lesch-Nyhan syndrome

Lesch-Nyhan syndrome is a hereditary disorder of purine metabolism causing overproduction of uric acid and neurological problems including spasticity, choreoathetosis, mental retardation, and compulsive self-mutilation. The syndrome is caused by a defect in the enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT), which converts guanine and hypoxanthine to the nucleotides GMP and IMP. There is evidence that the neurological problems are due to an adverse effect of the HPRT deficiency on the survival and/or development of dopaminergic neurons, specifically. Here we report that HPRT-deficient PC12 mutants that have a normal or near normal dopamine content (55–97% of that of wild-type cells) fail to undergo neuronal differentiation induced by nerve growth factor (NGF) when the de novo pathway of purine synthesis is partially inhibited. However, nerve growth factor-induced differentiation is near normal under these conditions in PC12 HPRT-deficient mutants containing much lower dopamine levels (<8% of that of wild type cells), indicating a neurotoxic effect of the endogenous dopamine in the mutants. The degree of inhibition of the de novo pathway of purine synthesis was the same in both classes of HPRT-deficient mutants. Expression of BCl-2 in a PC12 mutant that has a normal dopamine content allowed partial NGF-induced differentiation suggesting that the apoptotic pathway might be involved in the failure of differentiation when the de novo pathway of purine synthesis is partially inhibited. J. Neurosci. Res. 53:78–85, 1998. Published 1998 Wiley-Liss, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Gabapentin for self-injurious behavior in Lesch-Nyhan syndrome

Self-injurious behavior is a common clinical problem in children with Lesch-Nyhan syndrome, an X-linked disorder of purine metabolism. This behavior is not observed in other conditions associated with increased serum concentrations of uric acid, hypoxanthine, and xanthine. Various neurotransmitters appear to play a pivotal role in self-injurious behavior. The authors present a patient with Lesch-Nyhan syndrome, whose self-injurious behavior was effectively treated with gabapentin, and discuss possible mechanisms of action.     

Behavioral and neurochemical evaluation of a transgenic mouse model of Lesch-Nyhan syndrome

Two transgenic strains of mutant mice lacking hypoxanthine-guanidine phosphoribosyltransferase (HPRT) activity were examined behaviorally and neurochemically for phenotypic similarity to the human Lesch-Nyhan syndrome. In this syndrome, male children markedly deficient in the enzyme HPRT develop self-mutilation and severe motoric difficulties, and exhibit a pronounced deficiency of dopamine in the basal ganglia. The HPRT-deficient mice showed no evidence of self-mutilation, no detectable motor impairments on tests selected for sensitivity to basal ganglia dysfunction, and no differences in response to apomorphine. Biochemical analyses revealed significantly lower levels of striatal dopamine in the HPRT-deficient mice than in HPRT normal littermates, but the depletion was only of the order of 19%. The results suggest that mice lacking HPRT activity do not phenotypically resemble children born with the same enzymatic deficiency in part because mutant mouse striatal dopamine levels are not as low as those seen in clinical cases with Lesch-Nyhan disease. In contrast to Lesch-Nyhan children, mice may be able to utilize alternative pathways more effectively to maintain purine and neurotransmitter levels within the ranges required for normal brain development and function.     

Antero-ventral internal pallidum stimulation improves behavioral disorders in Lesch-Nyhan disease.

The Lesch-Nyhan syndrome is an X-linked recessive disorder caused by a deficiency in hypoxanthine-guanine phosphoribosyl transferase, a purine salvage enzyme. Affected individuals exhibit a characteristic neurobehavioral disorder with delayed acquisition of motor skills, dystonia, severe self-mutilations, and aggressive behavior. Deep brain stimulation has been previously proposed for controlling isolated involuntary movements and psychiatric disorders. We applied a double bilateral simultaneous stimulation to limbic and motor internal pallidum in one patient for controlling both behavioral and movement disorders, respectively. The injurious compulsions disappeared; dystonia and dyskinesia were decreased at 28 months follow-up.     

Brain benzodiazepine receptor binding and purine concentration in Lesch-Nyhan syndrome

Benzodiazepine receptor [( 3H]flunitrazepam) binding and purine concentration were measured in autopsied cerebral cortex of 4 patients who died with Lesch-Nyhan syndrome. Receptor density was normal in all 4 regions of Lesch-Nyhan cortex examined. However, an enhancement of benzodiazepine receptor affinity (25% reduction in Kd) was found in well-washed parietal and occipital cortex homogenates. Maximal gamma-aminobutyric acid (GABA) stimulation of [3H]flunitrazepam binding was normal in temporal, parietal and occipital cortex but markedly reduced (by 50-80%) in frontal cortex. Increased sensitivity to hypoxanthine inhibition (30% reduction in Ki) was also observed in parietal cortex. The concentrations of the purines hypoxanthine, xanthine and inosine in Lesch-Nyhan parietal cortex were about twice the values measured in control material matched for postmortem time. We suggest that the above-normal concentrations of purines estimated to be present in Lesch-Nyhan brain may be sufficient to significantly affect the ability of the benzodiazepine receptor to modulate GABA-mediated brain mechanisms.     

Monoamine deficiency in a transgenic (Hprt) mouse model of Lesch-Nyhan syndrome

The integrity of forebrain monoamine systems has been assessed both biochemically and immunohistochemically in transgenic mice carrying the mutant hprt-b^m2 gene, an animal model of Lesch-Nyhan syndrome. The mutant mice manifested 20–30% depletions of forebrain dopamine, and corresponding increase in dopamine turnover. By contrast, the mutant mice manifested normal tyrosine hydroxylase immunostaining of catecholamine cell bodies and terminals throughout the forebrain, and cell counts revealed no detectable loss of ventral mesencephalic dopamine neurones. Serotonin concentrations were also depleted, whereas no significant changes were found in noradrenaline or adrenaline, methylhydroxyphenylglycol (MHPG) or 5-hydroxyindoleacetic acid. The results indicate that a primary genetic deficiency in purine salvage pathways is associated with additional changes in forebrain monoamine metabolism in mouse as in man, although these changes are less pronounced in the animal model than in the human syndrome. The biochemical changes were not associated with explicit degeneration of the associated populations of neurones.     

Abnormal adenosine and dopamine receptor expression in lymphocytes of Lesch–Nyhan patients

Self-injurious behavior is the most outstanding feature of Lesch–Nyhan syndrome and has recently been ascribed to an obsessive–compulsive behavior. Lesch–Nyhan syndrome results from the complete enzyme deficiency of hypoxanthine–guanine phosphoribosyl transferase (HPRT) but the link between abnormal purine metabolism and its neurological and behavioral manifestations remains largely unknown. Previous studies led us to hypothesize that adenosine and dopamine receptor expression could be altered in HPRT-deficient cells. To test this hypothesis, we examined mRNA expressions of adenosine (ADORA2A and ADORA2B) and dopamine receptors (DRD1 and DRD2 like), and dopamine transporter (DAT1) in peripheral blood lymphocytes (PBLs) from Lesch–Nyhan patients. We also examined the influence of hypoxanthine in these expressions. As compared to normal PBLs, both ADORA2A and DRD5 expression were abnormal in PBLs from Lesch–Nyhan patients. In contrast, DAT1 expression was similar to control values in HPRT deficient PBLs. These results indicate an abnormal adenosine and dopamine receptor expression in HPRT-deficient cells and suggest disrupted adenosine and dopamine neurotransmission may have a significant role in the pathogenesis of the neurological manifestations of Lesch–Nyhan syndrome.     

Botulinum toxin as a novel treatment for self-mutilation in Lesch-Nyhan syndrome

Lesch-Nyhan syndrome (LNS) is an X-linked recessive disorder resulting from a deficiency of the metabolic enzyme hypozanthine-guanine phosphoribosyltransferase (HPRT). This syndrome presents with abnormal metabolic and neurological manifestations including hyperuricemia, mental retardation*, spastic cerebral palsy (CP), dystonia, and self-mutilation. The mechanism behind the severe self-mutilating behavior exhibited by patients with LNS is unknown and remains one of the greatest obstacles in providing care to these patients. This report describes a 10-year-old male child with confirmed LNS who was treated for self-mutilation of his hands, tongue, and lips with repeated botulinum toxin A (BTX-A) injections into the bilateral masseters. Our findings suggest that treatment with BTX-A affects both the central and peripheral nervous systems, resulting in reduced self-abusive behavior in this patient.     

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.