Clinical and biochemical studies on treatment of Lesch-Nyhan syndrome

Enzyme Replacement Therapy for Genetic Disorders Associated with Enzyme Deficiency

Mutations in human genes might lead to loss of functional proteins, causing diseases. Among these genetic disorders, a large class is associated with the deficiency in metabolic enzymes, resulting in both an increase in the concentration of substrates and a loss in the metabolites produced by the catalyzed reactions. The identification of therapeutic actions based on small molecules represents a challenge to medicinal chemists because the target is missing. Alternative approaches are biology-based, ranging from gene and stem cell therapy, CRISPR/Cas9 technology, distinct types of RNAs, and enzyme replacement therapy (ERT). This review will focus on the latter approach that since the 1990s has been successfully applied to cure many rare diseases, most of them being lysosomal storage diseases or metabolic diseases. So far, a dozen enzymes have been approved by FDA/EMA for lysosome storage disorders and only a few for metabolic diseases. Enzymes for replacement therapy are mainly produced in mammalian cells and some in plant cells and yeasts and are further processed to obtain active, highly bioavailable, less degradable products. Issues still under investigation for the increase in ERT efficacy are the optimization of enzymes interaction with cell membrane and internalization, the reduction in immunogenicity, and the overcoming of blood-brain barrier limitations when neuronal cells need to be targeted. Overall, ERT has demonstrated its efficacy and safety in the treatment of many genetic rare diseases, both saving newborn lives and improving patients' life quality, and represents a very successful example of targeted biologics.

Lesch-Nyhan Syndrome: Models, Theories, and Therapies

Lesch-Nyhan syndrome (LNS) is a rare X-linked disorder caused by mutations in HPRT1, an important enzyme in the purine salvage pathway. Symptoms of LNS include dystonia, gout, intellectual disability, and self-mutilation. Despite having been characterized over 50 years ago, it remains unclear precisely how deficits in hypoxanthine and guanine recycling can lead to such a profound neurological phenotype. Several studies have proposed different hypotheses regarding the etiology of this disease, and several treatments have been tried in patients, though none have led to a satisfactory explanation of the disease. New technologies such as next-generation sequencing, optogenetics, genome editing, and induced pluripotent stem cells provide a unique opportunity to map the precise sequential pathways leading from genotype to phenotype.

Intracellular ATP influences synaptic plasticity in area CA1 of rat hippocampus via metabolism to adenosine and activity-dependent activation of adenosine A1 receptors

The extent to which brain slices reflect the energetic status of the in vivo brain has been a subject of debate. We addressed this issue to investigate the recovery of energetic parameters and adenine nucleotides in rat hippocampal slices and the influence this has on synaptic transmission and plasticity. We show that, although adenine nucleotide levels recover appreciably within 10 min of incubation, it takes 3 h for a full recovery of the energy charge (to ≥ 0.93) and that incubation of brain slices at 34°C results in a significantly higher ATP/AMP ratio and a threefold lower activity of AMP-activated protein kinase compared with slices incubated at room temperature. Supplementation of artificial CSF with d-ribose and adenine (Rib/Ade) increased the total adenine nucleotide pool of brain slices, which, when corrected for the influence of the dead cut edges, closely approached in vivo values. Rib/Ade did not affect basal synaptic transmission or paired-pulse facilitation but did inhibit long-term potentiation (LTP) induced by tetanic or weak theta-burst stimulation. This decrease in LTP was reversed by strong theta-burst stimulation or antagonizing the inhibitory adenosine A(1) receptor suggesting that the elevated tissue ATP levels had resulted in greater activity-dependent adenosine release during LTP induction. This was confirmed by direct measurement of adenosine release with adenosine biosensors. These observations provide new insight into the recovery of adenine nucleotides after slice preparation, the sources of loss of such compounds in brain slices, the means by which to restore them, and the functional consequences of doing so.

Tetrabenazine therapy of pediatric hyperkinetic movement disorders

Tetrabenazine (TBZ), a presynaptic dopamine depletor and postsynaptic dopamine receptor blocker, is widely used for the treatment of hyperkinetic movement disorders in adults. However, reports of its use in children are limited. We review the efficacy and tolerability of TBZ therapy in 31 children with hyperkinetic movement disorders refractory to other medications. TBZ was effective in reducing the severity of movement disorders resistant to treatment with other medicines. When compared to adult patients, pediatric patients required higher doses. Side effects were similar to the adult population; however, children had a lower incidence of drug-induced Parkinsonism.

Delineation of the motor disorder of Lesch-Nyhan disease

Lesch-Nyhan disease (LND) is caused by deficiency of the purine salvage enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT). Affected individuals exhibit over-production of uric acid, along with a characteristic neurobehavioural syndrome that includes mental retardation, recurrent self-injurious behaviour and motor disability. Prior studies involving relatively small numbers of patients have provided different conclusions on the nature of the motor disorder. The current study includes the results of a multi-centre international prospective study of the motor disorder in the largest cohort of patients studied to date. A total of 44 patients ranging from 2 to 38 years presented a characteristic motor syndrome that involved severe action dystonia superimposed on baseline hypotonia. Although some patients also displayed other extrapyramidal or pyramidal signs, these were always less prominent than dystonia. These results are compared with a comprehensive review of 122 prior reports that included a total of 254 patients. Explanations for the differing observations available in the literature are provided, along with a summary of how the motor disorder of LND relates to current understanding of its pathophysiology involving the basal ganglia.

Lesch-Nyhan disease in a female with a clinically normal monozygotic twin

Lesch-Nyhan disease (LND) is an inborn error of purine metabolism caused by defective activity of the enzyme hypoxanthine guanine phosphoribosyl transferase (HPRT, EC 2.4.2.8), resulting from mutation in the corresponding gene on the long arm of the X chromosome (Xq26). The classic phenotype occurs almost exclusively in males and is characterized by hyperuricemia, mental retardation, severe dystonia, and self-injurious behavior. Heterozygous carrier females are usually clinically normal. However, a small number of clinically affected females have been described. In all previous cases there was a mutation in one HPRT allele and non-random inactivation of the X chromosome carrying the normal HPRT gene. We have analyzed a female MZ twin pair discordant for Lesch-Nyhan disease. The mother and both twins are heterozygous carriers of a HPRT splicing mutation (IVS8 + 4A > G; c.609 + 4A > G) and all three express the mutant allele at similar frequencies in peripheral blood T cells. The mother and one sister are clinically normal. In the affected twin, the clinical phenotype is classical for Lesch-Nyhan disease, despite the fact that HPRT activity in the blood was also normal. X inactivation analysis showed a skewed pattern in the fibroblasts of the affected twin sister, with the X chromosome carrying the normal HPRT allele preferentially inactivated. As in many other reported cases of X-linked diseases, the discordant phenotype of the two monozygous twin sisters suggests that the process responsible for monozygotic twinning can trigger skewed X inactivation.

The treatment of severe self-injurious behavior by the systematic fading of restraints: effects on self-injury, self-restraint, adaptive behavior, and behavioral correlates of affect

Severe self-injurious behavior (SIB) in people with mental retardation is difficult to treat when dangerously frequent or intense responding rules out functional analysis and interventions that permit free responding. This situation is common when restrictive devices, such as straight arm splints, are used. In this study, the effects of introducing flexion into a straight-arm splint, on SIB, self-restraint, adaptive behavior, and behavioral correlates of affect were examined for three individuals with severe mental retardation. Using single-case design methodology, for two individuals self-injury was reduced to zero, while the overall level of restriction was also significantly reduced. From the observed behavioral correlates of affect, there was no evidence of an increase in negative affect with the introduction of the new splint and the fading procedure, but there was evidence of an increase in positive vocalizations. Engagement in activities and social contact were not affected by the introduction of the new splint. The reasons for a decrease in SIB with a corresponding decrease in restriction in the absence of any manipulation of contingencies for SIB are discussed, with particular reference to stimulus control.

Effective behavioral treatment of self-biting by a child with Lesch-Nyhan syndrome

Behavior modification consisting of differential reinforcement of incompatible behavior and "punishment' was used for short periods at an early intervention center and was effective in eliminating self-biting of the arms, forearms and backs of the hands by a two-year-old with Lesch-Nyhan syndrome. No side-effects of the "punishment' component were observed. The effectiveness of the treatment was generalized to 3 1/2-hour sessions with his teacher at the early intervention center, and to the child's home. At six-month follow-up the teacher and parents indicated the continued absence of biting of the arms, forearms and back of the hands. The same treatment was applied to biting the fingers and the palms of the hands, without success.

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.

Treatment package to reduce SIB in a Lesch-Nyhan patient

Self-destructive behaviour in LNS children results in a tremendous burden to parents, teachers, staff members, and other responsible for their care. As constant vigilance is not always feasible, developing alternate methods of managing SIB becomes imperative. This report presents our efforts to improve the care of an LNS child and to ease the burden on staff members and parents by obtaining special devices (e.g. the custom-made mouthguard and the gloves) to prevent him from injuring himself. Others (e.g. Letts & Hobson, 1975) have likewise reported success in fabricating custom-designed chairs and devices in an effort to manage SIB in LNS children. Their devices were, however, more elaborate and much more expensive than the ones used in this report. The cost of obtaining a mouthguard similar to the one used with K. is estimated at between $20-$30 (US), while the gloves cost only $14.00. The major advantages of using such devices are that they safely allow employment of the extinction procedure along with allowing the child to participate more fully in activities of daily living. It is recognized that K. was in some ways an atypical Lesch-Nyhan child in that he possessed low normal receptive intelligence and scored fairly high (relative to most LNS children) on a test of verbal intelligence. His cognitive and verbal abilities made him a unique case in that he responded favourably to therapeutic instructions regarding relaxation and self-control tactics. The therapists were able to rely on K.'s verbalizations and feelings about his biting in structuring the treatment approach.(ABSTRACT TRUNCATED AT 250 WORDS)

Neonatal-6-hydroxydopamine treatment: model of susceptibility for self-mutilation in the Lesch-Nyhan syndrome

Neonatal-6-OHDA treated rats given L-DOPA after a decarboxylase inhibitor showed a high incidence of self-mutilation behavior (SMB) and self-biting. These behaviors were not observed in adult-6-OHDA-treated rats or in controls. Since inhibition of dopamine-beta-hydroxylase did not prevent or inhibit the SMB exhibited in neonatal-6-OHDA-treated rats after L-DOPA, norepinephrine is not likely to be contributing to this response. The age dependent effects observed are consistent with the hypothesis that neonatal reduction of dopamine-containing fibers is responsible for the SMB susceptibility observed in Lesch-Nyhan disease, making the neonatal-6-OHDA-treated rat a model of this neurological syndrome.

Behavior therapy for a child with Lesch-Nyhan syndrome

The behavioural symptoms in a 10-year-old boy with Lesch-Nyhan syndrome were effectively ameliorated by the behavior therapy techniques of systematic desensitization and extinction. Therapy was undertaken in a highly controlled environment. The hypothesis that the self-destructive behaviours in this syndrome were voluntary and maintained through continuous reinforcement was confirmed. Characteristic biting and other maladaptive behaviours were extinguished. Over a period of time it was possible to remove all the physical restraints previously used to prevent the boy injuring himself. During treatment his anxiety, associated with phobic reaction to being unrestrained, was reduced by nitrous oxide. At 1 1/2 years follow-up the boy continues to be symptom-free. He attends a special class at school and is learning to walk with crutches. It is emphasied that a trained and experienced therapist and a controlled environment are essential for the success of this form of behaviour therapy, and the dangers inherent in this method of treatment are discussed.

Double-blind clinical trial of 5-hydroxytryptophan in a case of Lesch-Nyhan syndrome

5-Hydroxytryptophan (5-HTP) treatment of a single case of Lesch-Nyhan syndrome showing compulsive self-mutilation, athetoid movements, and characteristic clinical biochemical picture was studied on a double-blind basis. 5-HTP or placebo was administered for seven fortnightly treatment blocks. 5-HTP produced a significant reduction of athetoid movement and a sedative effect but did not improve the patient's mood or reduce self-mutilation.

Immunological observations on patients with Lesch-Nyhan syndrome, and on the role of de-novo purine synthesis in lymphocyte transformation

Three patients with the Lesch-Nyhan syndrome were found to have normal delayed hypersensitivity, peripheral-blood T-lymphocyte counts, lymphocyte responses to P.H.A., and serum IgM, IgA, and IgE levels. However, the percentages of B-lymphocytes, IgG levels, serum-isohaemagglutinin titres, and lymphocyte responses to pokeweed mitogen (P.W.M.) were subnormal. These observations suggest that activity of the salvage pathway of purine synthesis catalysed by hypoxanthine-guanine phosphoribosyl transferase (H.G.P.R.T.) is not required for the responses of T-lymphocytes to mitogenic or antigenic stimulation, but may contribute to the proliferation and function of B lymphocytes. The major role of the de-novo pathway of purine synthesis in human lymphocyte responses to mitogenic or antigenic stimulation is shown by the effects of inhibitors of this pathway, including immunosuppressive agents, and by the effects of congenital deficiency or inhibition of adenosine deaminase.