Regional brain volume abnormalities in Lesch-Nyhan disease and its variants: a cross-sectional study

HGprt deficiency disrupts dopaminergic circuit development in a genetic mouse model of Lesch–Nyhan disease

In Lesch–Nyhan disease (LND), deficiency of the purine salvage enzyme hypoxanthine guanine phosphoribosyl transferase (HGprt) leads to a characteristic neurobehavioral phenotype dominated by dystonia, cognitive deficits and incapacitating self-injurious behavior. It has been known for decades that LND is associated with dysfunction of midbrain dopamine neurons, without overt structural brain abnormalities. Emerging post mortem and in vitro evidence supports the hypothesis that the dopaminergic dysfunction in LND is of developmental origin, but specific pathogenic mechanisms have not been revealed. In the current study, HGprt deficiency causes specific neurodevelopmental abnormalities in mice during embryogenesis, particularly affecting proliferation and migration of developing midbrain dopamine (mDA) neurons. In mutant embryos at E14.5, proliferation was increased, accompanied by a decrease in cell cycle exit and the distribution and orientation of dividing cells suggested a premature deviation from their migratory route. An abnormally structured radial glia-like scaffold supporting this mDA neuronal migration might lie at the basis of these abnormalities. Consequently, these abnormalities were associated with an increase in area occupied by TH⁺ cells and an abnormal mDA subpopulation organization at E18.5. Finally, dopaminergic innervation was disorganized in prefrontal and decreased in HGprt deficient primary motor and somatosensory cortices. These data provide direct in vivo evidence for a neurodevelopmental nature of the brain disorder in LND. Future studies should not only focus the specific molecular mechanisms underlying the reported neurodevelopmental abnormalities, but also on optimal timing of therapeutic interventions to rescue the DA neuron defects, which may also be relevant for other neurodevelopmental disorders.

Description of the Molecular and Phenotypic Spectrum of Lesch-Nyhan Disease in Eight Chinese Patients

Background: Lesch-Nyhan disease (LND) is a rare disorder involving pathogenic variants in the HPRT1 gene encoding the enzyme hypoxanthine-guanine phosphoribosyltransferase (HGPRT) that result in hyperuricemia, intellectual disability, dystonic movement disorder, and compulsive self-mutilation. The purpose of the present study was to characterize the genetic basis of LND and describe its phenotypic heterogeneity by identifying the variation in the HPRT1 gene in a cohort of Chinese LND patients. Results: The median age at diagnosis was 31 mo (interquartile range (IQR): 7-76 mo), and the initial manifestations were mainly head control weakness and motor development delay. The median age of self-mutilation behavior onset was 19 mo (IQR: 17-24 mo), and all patients were required to travel in a wheelchair and fall into the predicament of compulsive self-harm behavior. There were two patients whose blood uric acid levels were normal for their high urinary acid excretion fraction without taking uric acid-lowering drugs. Seven different pathogenic variants of the HPRT1 gene were identified among eight independent pedigrees, including four novel mutations [c.299 (exon 3) T > A; loss (exon: 6) 84 bp; c.277_281delATTGC; c.468_470delGAT]. The pathogenic variant sites were mainly concentrated in exon 3, and truncating mutations (including frameshift mutations and nonsense mutations) were the most common genetic variant types (5/7, 71.4%). Conclusion: The present study described the phenotypic and molecular spectrum of LND in eight Chinese families, including four novel mutations, which expands our understanding of LND.

Abnormalities of neural stem cells in Lesch-Nyhan disease

Lesch-Nyhan disease (LND) is a neurodevelopmental disorder caused by variants in the HPRT1 gene, which encodes the enzyme hypoxanthine-guanine phosphoribosyl transferase (HGprt). HGprt deficiency provokes numerous metabolic changes which vary among different cell types, making it unclear which changes are most relevant for abnormal neural development. To begin to elucidate the consequences of HGprt deficiency for developing human neurons, neural stem cells (NSCs) were prepared from 6 induced pluripotent stem cell (iPSC) lines from individuals with LND and compared to 6 normal healthy controls. For all 12 lines, gene expression profiles were determined by RNA-seq and protein expression profiles were determined by shotgun proteomics. The LND lines revealed significant changes in expression of multiple genes and proteins. There was little overlap in findings between iPSCs and NSCs, confirming the impact of HGprt deficiency depends on cell type. For NSCs, gene expression studies pointed towards abnormalities in WNT signaling, which is known to play a role in neural development. Protein expression studies pointed to abnormalities in the mitochondrial F0F1 ATPase, which plays a role in maintaining cellular energy. These studies point to some mechanisms that may be responsible for abnormal neural development in LND.

Microstructural white matter abnormalities in Lesch-Nyhan disease

Lesch-Nyhan disease is a rare, sex-linked, genetic neurodevelopmental disorder that is characterized by hyperuricemia, dystonia, cognitive impairment and recurrent self-injury. We previously found reduced brain white matter volume in patients with Lesch-Nyhan disease compared with healthy adults using voxel-based morphometry. Here, we address the structural integrity of white matter via diffusion tensor imaging. We hypothesized that white matter integrity would be decreased in men with Lesch-Nyhan disease and to a lesser extent in men with a milder variant of the disease (Lesch-Nyhan variant) relative to healthy men. After acquiring diffusion-weighted brain images from Lesch-Nyhan disease (n = 5), Lesch-Nyhan variant (n = 6) and healthy participants (n = 10), we used both tract-based spatial statistics and a regions of interest approach to analyse between-group fractional anisotropy differences. We first replicated earlier findings of reduced intracranial, grey matter and white matter volumes in patients. We then discovered marked reductions of fractional anisotropy relative to the healthy control group. The Lesch-Nyhan disease group showed more pronounced reductions in white matter integrity than the Lesch-Nyhan variant group. In addition to whole brain fractional anisotropy group differences, reductions in white matter integrity were observed in the corpus callosum, corona radiata, cingulum, internal capsule and superior longitudinal fasciculus. Moreover, the variant group had attenuated dystonia severity symptoms and cognitive deficits. These findings highlight the need to better understand the role of white matter in Lesch-Nyhan disease.

Potential molecular link between the β-amyloid precursor protein (APP) and hypoxanthine-guanine phosphoribosyltransferase (HGprt) enzyme in Lesch-Nyhan disease and cancer

Lesch-Nyhan disease (LND) is a rare X-linked inherited neurogenetic disorders of purine metabolic in which the cytoplasmic enzyme, hypoxanthine-guanine phosphoribosyltransferase (HGprt) is defective. Despite having been characterized over 60 years ago, however, up to now, there is no satisfactory explanation of how deficits in enzyme HGprt can lead to LND with the development of the persistent and severe self-injurious behavior. Recently, a role for epistasis between the mutated hypoxanthine phosphoribosyltransferase 1 (HPRT1) and the β-amyloid precursor protein (APP) genes affecting the regulation of alternative APP pre-mRNA splicing in LND has been demonstrated. Furthermore, there were also some reported cases of LND developing thrombosis while APP is an important regulator of vein thrombosis and controls coagulation. Otherwise, the surface expression of HGprt enzyme was also observed in several somatic tissue cancers while APP and the APP-like protein-2 (APLP2) are deregulated in cancer cells and linked to increased tumor cell proliferation, migration, and invasion. The present review provides a discussion about these findings and suggests a potential molecular link between APP and HGprt via epistasis between HPRT1 and APP genes affecting the regulation of alternative APP pre-mRNA splicing. As a perspective, expression vectors for HGprt enzyme and APP are constructed as described in Ref. # 24 (Nguyen KV, Naviaux RK, Nyhan WL (2020) Lesch-Nyhan disease: I. Construction of expression vectors for hypoxanthine-guanine phosphoribosyltransferase (HGprt) enzyme and amyloid precursor protein (APP). Nucleosides Nucleotides Nucleic Acids 39: 905–922), and they could be used as tools for clarification of these issues. In addition, these expression vectors, especially the one with the glycosyl-phosphatidylinositol (GPI) anchor can be used as a model for the construction of expression vectors for any protein targeting to the cell plasma membrane for studying intermolecular interactions and could be therefore useful in the vaccines as well as antiviral drugs development (studying intermolecular interactions between the spike glycoprotein of the severe acute respiratory syndrome coronavirus 2, SARS-CoV-2, as well as its variants and the angiotensin-converting enzyme 2, ACE2, in coronavirus disease 2019 (COVID-19) [43],[44], for example).

Movement Disorders and Renal Diseases

Movement disorders often emerge from the interplay of complex pathophysiological processes involving the kidneys and the nervous system. Tremor, myoclonus, ataxia, chorea, and parkinsonism can occur in the context of renal dysfunction (azotemia and electrolyte abnormalities) or they can be part of complications of its management (dialysis and renal transplantation). On the other hand, myoglobinuria from rhabdomyolysis in status dystonicus and certain drugs used in the management of movement disorders can cause nephrotoxicity. Distinct from these well-recognized associations, it is important to appreciate that there are several inherited and acquired disorders in which movement abnormalities do not occur as a consequence of renal dysfunction or vice versa but are manifestations of common pathophysiological processes affecting the nervous system and the kidneys. These disorders are the emphasis of this review. Increasing awareness of these conditions among neurologists may help them to identify renal involvement earlier, take timely intervention by anticipating complications and focus on therapies targeting common mechanisms in addition to symptomatic management of movement disorders. Recognition of renal impairment in a patient with complex neurological presentation may narrow down the differentials and aid in reaching a definite diagnosis.

Rescuing compounds for Lesch-Nyhan disease identified using stem cell-based phenotypic screening

Lesch-Nyhan disease (LND) is a rare monogenic disease caused by deficiency of the salvage pathway enzyme hypoxanthine-guanine phosphoribosyltransferase (HGPRT). LND is characterized by severe neuropsychiatric symptoms that currently cannot be treated. Predictive in vivo models are lacking for screening and evaluating candidate drugs because LND-associated neurological symptoms are not recapitulated in HGPRT-deficient animals. Here, we used human neural stem cells and neurons derived from induced pluripotent stem cells (iPSCs) of children affected with LND to identify neural phenotypes of interest associated with HGPRT deficiency to develop a target-agnostic-based drug screening system. We screened more than 3000 molecules and identified 6 pharmacological compounds, all possessing an adenosine moiety, that corrected HGPRT deficiency-associated neuronal phenotypes by promoting metabolism compensations in an HGPRT-independent manner. This included S-adenosylmethionine, a compound that had already been used as a compassionate approach to ease the neuropsychiatric symptoms in LND. Interestingly, these compounds compensate abnormal metabolism in a manner complementary to the gold standard allopurinol and can be provided to patients with LND via simple food supplementation. This experimental paradigm can be easily adapted to other metabolic disorders affecting normal brain development and functioning in the absence of a relevant animal model.

Clinical, biochemical and genetic characteristics of a cohort of 101 French and Italian patients with HPRT deficiency

BACKGROUND

HPRT deficiency is a rare disorder of purine metabolism whose natural history is not fully understood. No optimal management recommendations exist. The objective of the present study is to characterize a large cohort of patients with HPRT deficiency, comparing Lesch-Nyhan Disease (LND) and its attenuated variants, with the purpose of helping clinicians in disease management and prognostic definition.

METHODS

Genetic and clinical features of French and Italian patients with a confirmed diagnosis of HPRT deficiency were collected.

RESULTS

A hundred and one patients were studied, including 66 LND, 22 HND (HPRT-related Neurological Dysfunction) and 13 HRH (HPRT-Related Hyperuricemia) patients. The clinical manifestations at onset were not specific, but associated with an orange coloration of diapers in 22% of patients. The overall neurological involvement was more severe in LND than in HND patients. Behavioural disturbances were not limited to self-injuries and were not exclusive of LND. Median age of involuntary movements and self-injuries appearance in LND was 1.0 and 3 years, respectively. Renal manifestations (66.3% of patients) occurred at any age with a median onset age of 1.1 years, while gout (25.7% of patients) appeared later in disease course (median onset age 18 years) and was more frequent in attenuated variants than in LND. HPRT activity and genotype showed a significant correlation with the severity of the neurological disease. On the contrary, there were no significant differences in the development of nephropathy or gout. For the treatment of neurological aspects, botulinum toxin injections, oral or intrathecal baclofen and gabapentin were partially efficacious and well tolerated, while deep brain stimulation was associated to a worsening of patients' condition.

CONCLUSIONS

The present study improves the knowledge of the natural history of HPRT deficiency and could represent a starting point for the development of future management guidelines.

Characterization of the Basal Ganglia Using Diffusion Tensor Imaging in Children with Self-Injurious Behavior and Tuberous Sclerosis Complex

BACKGROUND AND PURPOSE

Tuberous sclerosis complex (TSC) is a rare, genetic disease that is associated with multiple manifestations including epilepsy and autism. Self‐injurious behaviors (SIBs) also occur in a subset of patients. This study used diffusion tensor imaging (DTI) in children with TSC for quantitative and volumetric analysis of brain regions that have been associated with SIB in other genetic conditions.

METHODS

We used DTI to compare 6 children with TSC‐associated SIB and 10 children with TSC without SIB. Atlas‐based analysis of DTI data and calculation of number of voxels; fractional anisotropy (FA); and mean, axial, and radial diffusivity were performed for multiple regions; DTI measures were summarized using medians and interquartile ranges and were compared using Wilcoxon rank sum tests and false discovery rates (FDRs).

RESULTS

Analysis showed that children with TSC and SIB had reduced numbers of voxels (median) in the bilateral globus pallidus (right: 218 vs. 260, P = .008, FDR = .18; left: 222 vs. 274, P = .002, FDR = .12) and caudate nucleus (right: 712 vs. 896, P = .01, FDR = .26; left: 702 vs. 921, P = .03, FDR = .44) and reduced FA in the bilateral globus pallidus (right: .233 vs. .272, P = .003, FDR = .12; left: .223 vs. .247, P = .004, FDR = .12) and left caudate nucleus (.162 vs. .186, P = .03, FDR = .39) versus children without SIB. No other statistically significant differences were found.

CONCLUSIONS

These data support a correlation between lower volumes of the globus pallidus and caudate with SIB in children with TSC.

Lesch-Nyhan syndrome and its variants: examining the behavioral and neurocognitive phenotype

PURPOSE OF REVIEW

Lesch-Nyhan Syndrome (LNS) is a metabolic disorder involving mutations in the HGPRT1 gene that result in hyperuricemia, intellectual disability, a dystonic movement disorder, and compulsive self-injury with self-mutilation. The aim of this review is to summarize recent research that documents the extended behavioral, neurologic, and neurocognitive phenotype in classic LNS, to describe milder variants of HGprt deficiency that do not self-injure and have less severe neurological and cognitive deficits, and to provide an update on treatment for associated psychiatric and behavioral disorders.

RECENT FINDINGS

Psychiatric management utilizes combined behavioral and pharmacological treatment in conjunction with protective equipment and dental management to avert self-injury. Pharmacological management focuses on stabilization of mood and anxiety management. S-adenosylmethionine (SAMe), a physiological intermediate in methylation and transsulfuration, has shown beneficial effects in carefully selected patients who can tolerate the drug. Deep brain stimulation is shown in several case reports and series to reduce or eliminate self-injury and aggression, and in some cases, modify dystonia.

SUMMARY

This review highlights progress in our understanding of the behavioral and neurocognitive phenotype of Lesch-Nyhan syndrome (HGprt deficiency) and its variants, describes psychiatric and behavioral management, and discusses prospects for new therapies.

Lesch-Nyhan disease in two families from Chiloé Island with mutations in the HPRT1 gene

Lesch-Nyhan disease (LND) is a rare X-linked inherited neurogenetic disorder of purine metabolism in which the enzyme, hypoxanthine-guanine phosphoribosyltransferase (HGprt) is defective. The authors report two independent point mutations leading to splicing errors: IVS 2 +1G>A, c.134 +1G>A, and IVS 3 +1G>A, c.318 +1G>A in the hypoxanthine-phosphoribosyltransferase1 (HPRT1) gene which result in exclusion of exon 2 and exon 3 respectively, in the HGprt enzyme protein from different members of two Chiloé Island families. Molecular analysis has revealed the heterogeneity of genetic mutation of the HPRT1 gene responsible for the HGprt deficiency. It allows fast, accurate carrier detection and genetic counseling.

A review of the implication of hypoxanthine excess in the physiopathology of Lesch-Nyhan disease

Lesch-Nyhan disease is caused by HGprt deficiency, however, the mechanism by which enzyme deficiency leads to the severe neurological manifestations is still unknown. We hypothesized that hypoxanthine excess leads, directly or indirectly, through its action in adenosine transport, to aberrations in neuronal development. We found that hypoxanthine diminishes adenosine transport and enhances stimulation of adenosine receptors. These effects cause an imbalance between adenosine, dopamine, and serotonin receptors in HGprt deficient cells, and cells differentiated with hypoxanthine showed an increase in dopamine, adenosine and serotonin receptors expression. Hypoxanthine deregulates early neuronal differentiation increasing WNT4 and EN1 gene expression.

Mutation in the Human HPRT1 Gene and the Lesch-Nyhan Syndrome

Lesch-Nyhan syndrome (LNS) is a rare X-linked inherited neurogenetic disorder of purine metabolism in which the enzyme, hypoxanthine-guanine phosphoribosyltransferase (HGprt) is defective. The authors report a novel mutation which led to HGprt-related neurological dysfunction (HND) in two brothers from the same family with a missense mutation in exon 6 of the coding region of the HPRT1 gene: c.437T>C, p.L146S. Molecular diagnosis discloses the genetic heterogeneity of the HPRT1 gene responsible for HGprt deficiency. It allows fast, accurate carrier detection and genetic counseling.

A double-blind, placebo-controlled, crossover trial of the selective dopamine D1 receptor antagonist ecopipam in patients with Lesch-Nyhan disease

Lesch-Nyhan disease (LND) is a genetic disorder that has characteristic metabolic, neurologic, and behavioral features. There are multiple behavioral problems including impulsivity, aggressiveness, and severe recurrent self-injurious behavior (SIB). This last behavior varies considerably across subjects and may encompass self-biting, self-hitting, scratching, head banging, and other injurious actions. Current treatments for SIB involve behavioral extinction, sedatives, physical restraints, and removal of teeth. Because these interventions do not reliably control SIB, better treatments are urgently needed. Animal studies have suggested that D1-dopamine receptor antagonists such as ecopipam may suppress SIB. These observations have led to proposals that such drugs might provide effective treatment for in LND. The current study describes the results of a double-blind, three-period, crossover trial of a single dose of ecopipam in subjects with LND. The study was designed for 20 patients, but it was terminated after recruitment of only 10 patients, because interim analysis revealed unanticipated side effects. These side effects were most likely related to starting with a single large dose without any titration phase. Despite the limited data due to early termination, the drug appeared to reduce SIB in most cases. Subjects who completed the trial were eligible to continue the drug in an open-label extension phase lasting a year, and one patient who elected to continue has maintained a striking reduction in SIB for more than a year with no apparent side effects. These results suggest ecopipam could be a useful treatment for SIB in, but further studies are needed to establish an appropriate dosing regimen.

A clinical trial of safety and tolerability for the selective dopamine D1 receptor antagonist ecopipam in patients with Lesch-Nyhan disease

Lesch-Nyhan disease (LND) is an inherited metabolic disorder characterized by the overproduction of uric acid and distinct behavioral, cognitive, and motor abnormalities. The most challenging clinical problem is self-injurious behavior (SIB), which includes self-biting, self-hitting, self-abrasion, and other features. Currently, these behaviors are managed by behavioral extinction, sedatives, physical restraints, and removal of teeth. More effective treatments are needed. Pre-clinical studies have led to the hypothesis that D1-dopamine receptor antagonists may provide useful treatments for SIB in LND. Ecopipam is one such selective D1-dopamine receptor antagonist. This report summarizes results of a dose-escalation study of the safety and tolerability of ecopipam in 5 subjects with LND. The results suggest that ecopipam is well tolerated, with sedation being the most common dose-limiting event. Several exploratory measures also suggest ecopipam might reduce SIB in this population. These results support the hypothesis that D1-dopamine receptor antagonists may be useful for suppressing SIB in LND, and encourage further studies of efficacy.

The Use of Perinatal 6-Hydroxydopamine to Produce a Rodent Model of Lesch-Nyhan Disease

Lesch-Nyhan disease is a neurologically, metabolically, and behaviorally devastating condition that has eluded complete characterization and adequate treatment. While it is known that the disease is intimately associated with dysfunction of the hypoxanthine phosphoribosyltransferase 1 (HPRT1) gene that codes for an enzyme of purine metabolism (hypoxanthine-guanine phosphoribosyltransferase) and is associated with neurological, behavioral, as well as metabolic dysfunction, the mechanisms of the neurobehavioral manifestations are as yet unclear. However, discoveries over the past few decades not only have created useful novel animal models (e.g., the HPRT-deficient mouse and the serendipitously discovered perinatal 6-hydroxydopamine (6-OHDA lesion model), but also have expanded into epigenetic, genomic, and proteomic approaches to better understand the mechanisms underlying this disease. The perinatal 6-OHDA model, in addition to modeling self-injury and dopamine depletion in the clinical condition, also underscores the profound importance of development in the differential course of maladaptive progression in the face of a common/single neurotoxic insult at different ages. Recent developments from clinical and basic science efforts attest to the fact that while the disease would seem to have a simple single gene defect at its core, the manifestations of this defect are profound and unexpectedly diverse. Future efforts employing the 6-OHDA model and others in the context of the novel technologies of genome editing, chemo- and opto-genetics, epigenetics, and further studies on the mechanisms of stress-induced maladaptations in brain all hold promise in taking our understanding of this disease to the next level.

Do clinical features of Lesch-Nyhan disease correlate more closely with hypoxanthine or guanine recycling?

Lesch-Nyhan disease (LND) is a rare, X-linked recessive neurodevelopmental disorder caused by deficiency of hypoxanthine-guanine phosphoribosyltransferase (HGprt), an enzyme in the purine salvage pathway. HGprt has two functions; it recycles hypoxanthine and guanine. Which of these two functions is more relevant for pathogenesis is unclear because some evidence points to hypoxanthine recycling, but other evidence points to guanine recycling. In this study, we selectively assayed hypoxanthine (Hprt) and guanine (Gprt) recycling in skin fibroblasts from 17 persons with LND, 11 with an attenuated variant of the disease (LNV), and 19 age-, sex-, and race-matched healthy controls (HC). Activity levels of both enzymes differed across groups (p < 0.0001), but only Gprt distinguished patients with LND from those with LNV (p < 0.05). Gprt also showed slightly stronger correlations than Hprt with 13 of 14 measures of the clinical phenotype, including the severity of dystonia, cognitive impairment, and behavioral abnormalities. These findings suggest that loss of guanine recycling might be more closely linked to the LND/LNV phenotype than loss of hypoxanthine recycling.

In Vivo NMR Studies of the Brain with Hereditary or Acquired Metabolic Disorders

Metabolic disorders, whether hereditary or acquired, affect the brain, and abnormalities of the brain are related to cellular integrity; particularly in regard to neurons and astrocytes as well as interactions between them. Metabolic disturbances lead to alterations in cellular function as well as microscopic and macroscopic structural changes in the brain with diabetes, the most typical example of metabolic disorders, and a number of hereditary metabolic disorders. Alternatively, cellular dysfunction and degeneration of the brain lead to metabolic disturbances in hereditary neurological disorders with neurodegeneration. Nuclear magnetic resonance (NMR) techniques allow us to assess a range of pathophysiological changes of the brain in vivo. For example, magnetic resonance spectroscopy detects alterations in brain metabolism and energetics. Physiological magnetic resonance imaging (MRI) detects accompanying changes in cerebral blood flow related to neurovascular coupling. Diffusion and T1/T2-weighted MRI detect microscopic and macroscopic changes of the brain structure. This review summarizes current NMR findings of functional, physiological and biochemical alterations within a number of hereditary and acquired metabolic disorders in both animal models and humans. The global view of the impact of these metabolic disorders on the brain may be useful in identifying the unique and/or general patterns of abnormalities in the living brain related to the pathophysiology of the diseases, and identifying future fields of inquiry.

Hypoxanthine deregulates genes involved in early neuronal development. Implications in Lesch-Nyhan disease pathogenesis

Neurological manifestations in Lesch-Nyhan disease (LND) are attributed to the effect of hypoxanthine-guanine phosphoribosyltransferase (HPRT) deficiency on the nervous system development. HPRT deficiency causes the excretion of increased amounts of hypoxanthine into the extracellular medium and we hypothesized that HPRT deficiency related to hypoxanthine excess may then lead, directly or indirectly, to transcriptional aberrations in a variety of genes essential for the function and development of striatal progenitor cells. We have examined the effect of hypoxanthine excess on the differentiation of neurons in the well-established human NTERA-2 cl.D1 (NT2/D1) embryonic carcinoma neurogenesis model. NT2/D1 cells differentiate along neuroectodermal lineages after exposure to retinoic acid (RA). Hypoxanthine effects on RA-differentiation were examined by the changes on the expression of various transcription factor genes essential to neuronal differentiation and by the changes in tyrosine hydroxylase (TH), dopamine, adenosine and serotonin receptors (DRD, ADORA, HTR). We report that hypoxanthine excess deregulate WNT4, from Wnt/β-catenin pathway, and engrailed homeobox 1 gene and increased TH and dopamine DRD1, adenosine ADORA2A and serotonin HTR7 receptors, whose over expression characterize early neuro-developmental processes.

Epigenetic Regulation in Amyloid Precursor Protein with Genomic Rearrangements and the Lesch-Nyhan Syndrome

Recently, epigenetic regulation of alternative APP pre-mRNA splicing in the Lesch-Nyhan syndrome (LNS) has been studied (see Ref. 7) and showed for the first time, the presence of several APP-mRNA isoforms encoding divers APP protein isoforms ranging from 120 to 770 amino acids (with or without mutations and/or deletions). Here, by continuing on this work, I identified, for the first time new APP-mRNA isoforms with a deletion followed by an insertion (INDELS) in LNS and LNVs patients: c.19_2295delinsG166TT…GAGTCC…CTTAGTC…TCT489,p.Leu7Valfs*2;c.19_2295 delinsG169TT…GAGACC…CTTGGTC…TCT492,p.Leu7Valfs*2;and c.16_2313delinsG84CC…CAT616,p.Leu7Hisfs*45. A role of genomic rearrangements of APP gene via the Fork Stalling and Template Switching (FoSTeS) mechanism leading to INDELS was suggested. Epistasis between mutated HPRT1 and APP genes could be one of the factors of epigenetic modifications responsible for genomic rearrangements of APP gene. My findings accounted for epigenetic mechanism in the regulation of alternative APP pre-mRNA splicing as well as for epigenetic control of genomic rearrangements of APP gene may provide therefore new directions not only for investigating the role of APP in neuropathology associated with HGprt-deficiency in LNS and LNVs patients but also for the research in neurodevelopmental and neurodegenerative disorders by which APP gene involved in the pathogenesis of the diseases such as autism, fragile X syndrome (FXS), and Alzheimer's disease (AD) with its diversity and complexity, especially for sporadic form of AD (SAD). An accurate quantification of various APP-mRNA isoforms in brain tissues for detection of initial pathological changes or pathology development is needed and antisense drugs are the potential treatments.

New biomarkers for early diagnosis of Lesch-Nyhan disease revealed by metabolic analysis on a large cohort of patients

BACKGROUND

Lesch-Nyhan disease is a rare X-linked neurodevelopemental metabolic disorder caused by a wide variety of mutations in the HPRT1 gene leading to a deficiency of the purine recycling enzyme hypoxanthine-guanine phosphoribosyltransferase (HGprt). The residual HGprt activity correlates with the various phenotypes of Lesch-Nyhan (LN) patients and in particular with the different degree of neurobehavioral disturbances. The prevalence of this disease is considered to be underestimated due to large heterogeneity of its clinical symptoms and the difficulty of diagnosing of the less severe forms of the disease. We therefore searched for metabolic changes that would facilitate an early diagnosis and give potential clues on the disease pathogenesis and potential therapeutic approaches.

METHODS

Lesch-Nyhan patients were diagnosed using HGprt enzymatic assay in red blood cells and identification of the causal HPRT1 gene mutations. These patients were subsequently classified into the three main phenotypic subgroups ranging from patients with only hyperuricemia to individuals presenting motor dysfunction, cognitive disability and self-injurious behavior. Metabolites from the three classes of patients were analyzed and quantified by High Performance Ionic Chromatography and biomarkers of HGprt deficiency were then validated by statistical analyses.

RESULTS

A cohort of 139 patients, from 112 families, diagnosed using HGprt enzymatic assay in red blood cells, was studied. 98 displayed LN full phenotype (86 families) and 41 (26 families) had attenuated clinical phenotypes. Genotype/phenotype correlations show that LN full phenotype was correlated to genetic alterations resulting in null enzyme function, while variant phenotypes are often associated with missense mutations allowing some residual HGprt activity. Analysis of metabolites extracted from red blood cells from 56 LN patients revealed strong variations specific to HGprt deficiency for six metabolites (AICAR mono- and tri-phosphate, nicotinamide, nicotinic acid, ATP and Succinyl-AMP) as compared to controls including hyperuricemic patients without HGprt deficiency.

CONCLUSIONS

A highly significant correlation between six metabolites and the HGprt deficiency was established, each of them providing an easily measurable marker of the disease. Their combination strongly increases the probability of an early and reliable diagnosis for HGprt deficiency.

Treatment of motor and behavioural symptoms in three Lesch-Nyhan patients with intrathecal baclofen

Current therapies for the Lesch-Nyhan Syndrome (OMIM: 300322) are off-label and experimental, often leading to inconsistent outcomes. We here report the effects of an intrathecal baclofen therapy, carried out at the Scientific Institute Eugenio Medea (Lecco, Italy), on three patients who no longer received benefit from previous therapies. This treatment, as expected, ameliorated the motor symptoms and, unexpectedly, it also improved behavioural components. This result may involve a functional interaction between baclofen and dopamine, complemented by an anxiolytic effect. Our observations provide the rationale for the use of intrathecal baclofen administration in the therapy of the Lesch-Nyhan Syndrome.

Brain white matter volume abnormalities in Lesch-Nyhan disease and its variants

OBJECTIVE

We sought to examine brain white matter abnormalities based on MRI in adults with Lesch-Nyhan disease (LND) or an attenuated variant (LNV) of this rare, X-linked neurodevelopmental disorder of purine metabolism.

METHODS

In this observational study, we compared 21 adults with LND, 17 with LNV, and 33 age-, sex-, and race-matched healthy controls using voxel-based morphometry and analysis of covariance to identify white matter volume abnormalities in both patient groups.

RESULTS

Patients with classic LND showed larger reductions of white (26%) than gray (17%) matter volume relative to healthy controls. Those with LNV showed comparable reductions of white (14%) and gray (15%) matter volume. Both patient groups demonstrated reduced volume in medial inferior white matter regions. Compared with LNV, the LND group showed larger reductions in inferior frontal white matter adjoining limbic and temporal regions and the motor cortex. These regions likely include such long association fibers as the superior longitudinal and uncinate fasciculi.

CONCLUSIONS

Despite earlier reports that LND primarily involves the basal ganglia, this study reveals substantial white matter volume abnormalities. Moreover, white matter deficits are more severe than gray matter deficits in classic LND, and also characterize persons with LNV. The brain images acquired for these analyses cannot precisely localize white matter abnormalities or determine whether they involve changes in tract orientation or anisotropy. However, clusters of reduced white matter volume identified here affect regions that are consistent with the neurobehavioral phenotype.

Lateralized effect of pallidal stimulation on self-mutilation in Lesch-Nyhan disease

Lesch-Nyhan disease (LND) is an X-linked hereditary disorder caused by a deficiency of hypoxanthine-guanine phosphoribosyltransferase. This syndrome is characterized by hyperuricemia, self-mutilation, cognitive impairment, and movement disorders such as spasticity and dystonia. The authors describe the case of a 15-year-old boy who underwent bilateral placement of globus pallidus internus (GPi) deep brain stimulation (DBS) electrodes for the treatment of generalized dystonia. His self-mutilating behavior gradually disappeared several weeks after the start of GPi stimulation. The dystonia and self-mutilating behavior returned on the left side only after a right lead fracture. This case is the first reported instance of LND treated with DBS in which the stimulation was interrupted and the self-mutilation returned in a lateralized fashion. The findings indicate that the neurobehavioral aspect of LND is lateralized and that contralateral GPi stimulation is responsible for lateralized improvement in self-injurious behavior.

Genotypic and phenotypic spectrum in attenuated variants of Lesch-Nyhan disease

Lesch-Nyhan disease and its attenuated variants are caused by deficiency of the purine salvage enzyme, hypoxanthine-guanine phosphoribosyltransferase (HGprt). All patients exhibit excessive production of uric acid, which increases the risk for nephrolithiasis, renal failure, gouty arthritis and tophi. The mildest phenotype includes only problems related to overproduction of uric acid. The most severe clinical phenotype includes prominent neurological abnormalities and the universal feature is self-injurious behavior. In between the mildest and most severe syndromes is a broad spectrum of phenotypes with varying degrees of neurological, neurocognitive and behavioral abnormalities. The effect of HPRT1 gene mutations on residual HGprt enzyme activity is the most relevant factor contributing to disease phenotype. Attenuated clinical phenotypes are associated with residual enzyme function, whereas the most severe phenotype is usually associated with null activity. In cases of gouty arthritis with urate overproduction, a careful evaluation for motor impairments or neurocognitive abnormalities may help to identify attenuated variants of Lesch-Nyhan disease for better management.

Loss of dopamine phenotype among midbrain neurons in Lesch-Nyhan disease

OBJECTIVE

Lesch-Nyhan disease (LND) is caused by congenital deficiency of the purine recycling enzyme, hypoxanthine-guanine phosphoribosyltransferase (HGprt). Affected patients have a peculiar neurobehavioral syndrome linked with reductions of dopamine in the basal ganglia. The purpose of the current studies was to determine the anatomical basis for the reduced dopamine in human brain specimens collected at autopsy.

METHODS

Histopathological studies were conducted using autopsy tissue from 5 LND cases and 6 controls. Specific findings were replicated in brain tissue from an HGprt-deficient knockout mouse using immunoblots, and in a cell model of HGprt deficiency by flow-activated cell sorting (FACS).

RESULTS

Extensive histological studies of the LND brains revealed no signs suggestive of a degenerative process or other consistent abnormalities in any brain region. However, neurons of the substantia nigra from the LND cases showed reduced melanization and reduced immunoreactivity for tyrosine hydroxylase (TH), the rate-limiting enzyme in dopamine synthesis. In the HGprt-deficient mouse model, immunohistochemical stains for TH revealed no obvious loss of midbrain dopamine neurons, but quantitative immunoblots revealed reduced TH expression in the striatum. Finally, 10 independent HGprt-deficient mouse MN9D neuroblastoma lines showed no signs of impaired viability, but FACS revealed significantly reduced TH immunoreactivity compared to the control parent line.

INTERPRETATION

These results reveal an unusual phenomenon in which the neurochemical phenotype of dopaminergic neurons is not linked with a degenerative process. They suggest an important relationship between purine recycling pathways and the neurochemical integrity of the dopaminergic phenotype.

Epigenetic regulation in amyloid precursor protein and the Lesch-Nyhan syndrome

Lesch-Nyhan syndrome (LNS) is a neurogenetic disorder of purine metabolism in which the enzyme, hypoxanthine-guanine phosphoribosyltransferase (HPRT) is defective. A major unsolved question is how the loss of HPRT enzyme function affects the brain to cause the neurobehavioural syndrome in LNS and its attenuated variants (LNVs). To address this issue, a search for a link between LNS and the amyloid precursor protein (APP) is developed. Here, I identified, for the first time in fibroblasts from normal subjects as well as from LNS and LNV patients: (a) several APP-mRNA isoforms encoding divers APP protein isoforms ranging from 120 to 770 amino acids (with or without mutations and/or deletions) accounted for epigenetic mechanisms in the regulation of alternative APP pre-mRNA splicing and (b) five novel independent polymorphisms in the APP promoter: -956A>G, -1023T>C, -1161A>G, -2224G>A, -2335C>T relative to the transcription start site. A role for epistasis between mutated HPRT and APP genes affecting the regulation of alternative APP pre-mRNA splicing in LNS is suggested. An accurate quantification of various APP isoforms in brain tissues for detection of initial pathological changes or pathology development is needed. My findings may provide new directions not only for investigating the role of APP in neuropathology associated with HPRT-deficiency in LNS but also for the research in neurodevelopmental and neurodegenerative disorders by which various APP isoforms involved in the pathogenesis of the diseases such as Alzheimer's disease.