Attenuated variants of Lesch-Nyhan disease

Metabolic and neurobehavioral disturbances induced by purine recycling deficiency in Drosophila

Adenine phosphoribosyltransferase (APRT) and hypoxanthine-guanine phosphoribosyltransferase (HGPRT) are two structurally related enzymes involved in purine recycling in humans. Inherited mutations that suppress HGPRT activity are associated with Lesch-Nyhan disease (LND), a rare X-linked metabolic and neurological disorder in children, characterized by hyperuricemia, dystonia, and compulsive self-injury. To date, no treatment is available for these neurological defects and no animal model recapitulates all symptoms of LND patients. Here, we studied LND-related mechanisms in the fruit fly. By combining enzymatic assays and phylogenetic analysis, we confirm that no HGPRT activity is expressed in Drosophila melanogaster, making the APRT homolog (Aprt) the only purine-recycling enzyme in this organism. Whereas APRT deficiency does not trigger neurological defects in humans, we observed that Drosophila Aprt mutants show both metabolic and neurobehavioral disturbances, including increased uric acid levels, locomotor impairments, sleep alterations, seizure-like behavior, reduced lifespan, and reduction of adenosine signaling and content. Locomotor defects could be rescued by Aprt re-expression in neurons and reproduced by knocking down Aprt selectively in the protocerebral anterior medial (PAM) dopaminergic neurons, the mushroom bodies, or glia subsets. Ingestion of allopurinol rescued uric acid levels in Aprt-deficient mutants but not neurological defects, as is the case in LND patients, while feeding adenosine or N6-methyladenosine (m6A) during development fully rescued the epileptic behavior. Intriguingly, pan-neuronal expression of an LND-associated mutant form of human HGPRT (I42T), but not the wild-type enzyme, resulted in early locomotor defects and seizure in flies, similar to Aprt deficiency. Overall, our results suggest that Drosophila could be used in different ways to better understand LND and seek a cure for this dramatic disease.

Psychiatric Manifestations in Children and Adolescents with Inherited Metabolic Diseases

Background: Inherited metabolic disorders (IEMs) can be represented in children and adolescents by psychiatric disorders. The early diagnosis of IEMs is crucial for clinical outcome and treatment. The aim of this review is to analyze the most recurrent and specific psychiatric features related to IEMs in pediatrics, based on the onset type and psychiatric phenotypes. Methods: Following the PRISMA Statement, a systematic literature review was performed using a predefined algorithm to find suitable publications in scientific databases of interest. After removing duplicates and screening titles and abstracts, suitable papers were analyzed and screened for inclusion and exclusion criteria. Finally, the data of interest were retrieved from the remaining articles. Results: The results of this study are reported by type of symptoms onset (acute and chronic) and by possible psychiatric features related to IEMs. Psychiatric phenomenology has been grouped into five main clinical manifestations: mood and anxiety disorders; schizophrenia-spectrum disorders; catatonia; eating disorders; and self-injurious behaviors. Conclusions: The inclusion of a variety of psychiatric manifestations in children and adolescents with different IEMs is a key strength of this study, which allowed us to explore the facets of seemingly different disorders in depth, avoiding possible misdiagnoses, with the related delay of early and appropriate treatments.

A new physiological medium uncovers biochemical and cellular alterations in Lesch-Nyhan disease fibroblasts

BACKGROUND

Lesch-Nyhan disease (LND) is a severe neurological disorder caused by the genetic deficiency of hypoxanthine-guanine phosphoribosyltransferase (HGprt), an enzyme involved in the salvage synthesis of purines. To compensate this deficiency, there is an acceleration of the de novo purine biosynthetic pathway. Most studies have failed to find any consistent abnormalities of purine nucleotides in cultured cells obtained from the patients. Recently, it has been shown that 5-aminoimidazole-4-carboxamide riboside 5'-monophosphate (ZMP), an intermediate of the de novo pathway, accumulates in LND fibroblasts maintained with RPMI containing physiological levels (25 nM) of folic acid (FA), which strongly differs from FA levels of regular cell culture media (2200 nM). However, RPMI and other standard media contain non-physiological levels of many nutrients, having a great impact in cell metabolism that does not precisely recapitulate the in vivo behavior of cells.

METHODS

We prepared a new culture medium containing physiological levels of all nutrients, including vitamins (Plasmax-PV), to study the potential alterations of LND fibroblasts that may have been masked by the usage of non-physiological media. We quantified ZMP accumulation under different culture conditions and evaluated the activity of two known ZMP-target proteins (AMPK and ADSL), the mRNA expression of the folate carrier SLC19A1, possible mitochondrial alterations and functional consequences in LND fibroblasts.

RESULTS

LND fibroblasts maintained with Plasmax-PV show metabolic adaptations such a higher glycolytic capacity, increased expression of the folate carrier SCL19A1, and functional alterations such a decreased mitochondrial potential and reduced cell migration compared to controls. These alterations can be reverted with high levels of folic acid, suggesting that folic acid supplements might be a potential treatment for LND.

CONCLUSIONS

A complete physiological cell culture medium reveals new alterations in Lesch-Nyhan disease. This work emphasizes the importance of using physiological cell culture conditions when studying a metabolic disorder.

Neurological presentations of inborn errors of purine and pyrimidine metabolism

Purines and pyrimidines are essential components as they are the building blocks of vital molecules, such as nucleic acids, coenzymes, signalling molecules, as well as energy transfer molecules. Purine and pyrimidine metabolism defects are characterised by abnormal concentrations of purines, pyrimidines and/or their metabolites in cells or body fluids. This phenomenon is due to a decreased or an increased activity of enzymes involved in this metabolism and has been reported in humans for over 60 years. This review provides an overview of neurological presentations of inborn errors of purine and pyrimidine metabolism. These conditions can lead to psychomotor retardation, epilepsy, hypotonia, or microcephaly; sensory involvement, such as deafness and visual disturbances; multiple malformations, as well as muscular symptoms. Clinical signs are often nonspecific and thus overlooked, but some diseases are treatable and early diagnosis may improve the child's future. Although these metabolic hereditary diseases are rare, they are most probably under-diagnosed. When confronted with suggestive clinical or laboratory signs, clinicians should prescribe genetic testing in association with a biochemical screening including thorough purine and pyrimidine metabolites analysis and/or specific enzyme evaluation. This is most likely going to increase the number of confirmed patients.

Single-Electrode Deep Brain Stimulation of Bilateral Posterolateral Globus Pallidus Internus in Patients With Medically Resistant Lesch-Nyhan Syndrome

Deep brain stimulation (DBS) targeting various locations within the globus pallidus internus (GPi) is emerging as a therapeutic option for patients with medically resistant Lesch-Nyhan syndrome. We report our institutional experience with single-electrode DBS in the bilateral posterolateral GPi as an effective method for reduction of both dystonia and self-injurious behavior. Two pediatric patients aged six and 14 years underwent implantation of bilateral singular DBS leads in the posterolateral GPi and were followed postoperatively through the programming process and symptomatic improvements. Caregivers reported that after DBS in the posterolateral GPi, these patients experienced decreased self-mutilation behavior and decreased dystonia.

Deep brain stimulation in Lesch-Nyhan syndrome: a systematic review

Given the good results of deep brain stimulation (DBS) in the treatment of movement disorders, DBS was initially tried to treat Lesch-Nyhan syndrome (LNS) with the aim to alleviate LNS-related dystonia. Some cases have reported clinical results of DBS in LNS thus far. This systematic review was conducted to comprehensively summarize cases of LNS treated with DBS and evaluate the efficacy and safety of DBS in LNS. Eight publications covering 12 LNS patients were included in this review. DBS improved dystonia of the LNS to varying degrees. All the included cases achieved partial or complete control of self-injurious behavior (SIB). Overall, DBS is a promising treatment for both motor and behavior disorders of LNS patients, but the results reported thus far have varied widely, especially for motor outcomes. The ultimate clinical benefits in LNS patients were still unpredictable. DBS-related complications were rather common, which raised questions about the safety of the procedure in LNS. More research is needed to further clarify the safety and effectiveness of this treatment.

The apparent paradox of phenotypic diversity and shared mechanisms across dystonia syndromes

PURPOSE OF REVIEW

We describe here how such mechanisms shared by different genetic forms can give rise to motor performance dysfunctions with a clinical aspect of dystonia.

RECENT FINDINGS

The continuing discoveries of genetic causes for dystonia syndromes are transforming our view of these disorders. They share unexpectedly common underlying mechanisms, including dysregulation in neurotransmitter signaling, gene transcription, and quality control machinery. The field has further expanded to include forms recently associated with endolysosomal dysfunction.

SUMMARY

The discovery of biological pathways shared between different monogenic dystonias is an important conceptual advance in the understanding of the underlying mechanisms, with a significant impact on the pathophysiological understanding of clinical phenomenology. The functional relationship between dystonia genes could revolutionize current dystonia classification systems, classifying patients with different monogenic forms based on common pathways. The most promising effect of these advances is on future mechanism-based therapeutic approaches.

Congenital anomalies-associated Riga-Fede disease as an early manifestation of Lesch-Nyhan syndrome: rare entities in the same pediatric patient-a case report

Background

Riga–Fede disease is a rare begnin disorder of the oral tissues, it can be associated with congenital anomalies and neurological disturbances. Lesch–Nyhan syndrome is a rare X-linked recessive disorder characterized by neurological and behavioral manifestations. A patient can rarely be diagnosed with both diseases in a lifetime. Therefore, reporting manifestations from such disorders is important to avoid misdiagnosis and help in timely intervention.

Case presentation

This case report presents an 8-months-old male infant with traumatic oral ulcers from deciduous teeth. A diagnosis of Riga–Fede disease was made. Teeth grinding was performed and the oral lesions were healed. At the age of 2.5 years, the patient presented with neurological manifestations as well as facial tissue and premature teeth loss from self mutilation. Genetic sequencing revealed a variant of uncertain significance in the Hypoxanthine Phosphoribosyltransferase 1 gene. He was diagnosed with Lesch–Nyhan syndrome. Cleft palate, ventricular septal defect, congenitally undescended testis and ectopic left iliac kidney were also reported. The patient was scheduled on psychiatric treatment and after about six months of follow-up, both the behavioral and neurological symptoms were improved.

Conclusions

Riga–Fede disease can be an early manifestation of Lesch–Nyhan syndrome. To the best of our knowledge, this is the first reported case with the incidence of all the mentioned entities in one pediatric patient.

Oromandibular dystonia – A systematic review

Oromandibular dystonia (OMD) is a clinical problem which is commonly encountered in the practice of movement disorders. OMD results from a variety of genetic and acquired etiologies and can occur as an isolated manifestation, or as part of an isolated generalized or a combined dystonia syndrome. There are only very few systematic reviews on this condition which often causes significant disability. We review here the etiology, clinical features, diagnostic approach and management of OMD.

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.

Deep brain stimulation in Lesch-Nyhan disease: outcomes from the patient's perspective

AIM

To provide insight into outcome and long-term safety and efficacy of deep brain stimulation (DBS), from the perspective of individuals with Lesch-Nyhan disease (LND) and their families.

METHOD

We used patient-centered outcome measures to assess long-term outcomes of DBS for 14 individuals (mean [SD] age 10y 10mo [5y 6mo], range 5-23y, all males) with LND, after an average duration of 5y 6mo (range 11mo-10y 5mo) after surgery. We compared these results with a comprehensive review of previously published cases.

RESULTS

Patients and their families reported that DBS of the globus pallidus can be effective both for motor and behavioral disturbances in LND. However, outcome measures were often not significantly changed owing to substantial variability among individuals, and were overall less positive than in previous reports based on clinician assessments. In addition, there was an unexpectedly high rate of adverse events, tempering overall enthusiasm for the procedure.

INTERPRETATION

Although DBS might be an effective treatment for LND, more research is needed to understand the reasons for response variability and the unusually high rates of adverse events before DBS can be recommended for these patients. What this paper adds Individuals with Lesch-Nyhan disease and their families report variable efficacy of deep brain stimulation. Long-term outcomes are associated with a high adverse event rate.

Lesch-Nyhan disease causes impaired energy metabolism and reduced developmental potential in midbrain dopaminergic cells

Mutations in HPRT1, a gene encoding a rate-limiting enzyme for purine salvage, cause Lesch-Nyhan disease which is characterized by self-injury and motor impairments. We leveraged stem cell and genetic engineering technologies to model the disease in isogenic and patient-derived forebrain and midbrain cell types. Dopaminergic progenitor cells deficient in HPRT showed decreased intensity of all developmental cell-fate markers measured. Metabolic analyses revealed significant loss of all purine derivatives, except hypoxanthine, and impaired glycolysis and oxidative phosphorylation. real-time glucose tracing demonstrated increased shunting to the pentose phosphate pathway for de novo purine synthesis at the expense of ATP production. Purine depletion in dopaminergic progenitor cells resulted in loss of RHEB, impairing mTORC1 activation. These data demonstrate dopaminergic-specific effects of purine salvage deficiency and unexpectedly reveal that dopaminergic progenitor cells are programmed to a high-energy state prior to higher energy demands of terminally differentiated cells.

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.

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.

Deep Brain Stimulation of the Internal Pallidum in Lesch-Nyhan Syndrome: Clinical Outcomes and Connectivity Analysis

BACKGROUND

Lesch-Nyhan syndrome (LNS) is a rare genetic disorder characterized by a deficiency of hypoxanthine-guanine phosphoribosyltransferase enzyme. It manifests during infancy with compulsive self-mutilation behavior associated with disabling generalized dystonia and dyskinesia. Clinical management of these patients poses an enormous challenge for medical teams and carers.

OBJECTIVES

We report our experience with bilateral deep brain stimulation (DBS) of the globus pallidus internus (GPi) in the management of this complex disorder.

MATERIALS AND METHODS

Preoperative and postoperative functional assessment data prospectively collected by a multidisciplinary pediatric complex motor disorders team, including imaging, neuropsychology, and neurophysiology evaluations were analyzed with regards to motor and behavioral control, goal achievement, and patient and caregivers' expectations.

RESULTS

Four male patients (mean age 13 years) underwent DBS implantation between 2011 and 2018. Three patients received double bilateral DBS electrodes within the posteroventral GPi and the anteromedial GPi, whereas one patient had bilateral electrodes placed in the posteroventral GPi only. Median follow-up was 47.5 months (range 22-98 months). Functional improvement was observed in all patients and discussed in relation to previous reports. Analysis of structural connectivity revealed significant correlation between the involvement of specific cortical regions and clinical outcome.

CONCLUSION

Combined bilateral stimulation of the anteromedial and posteroventral GPi may be considered as an option for managing refractory dystonia and self-harm behavior in LNS patients. A multidisciplinary team-based approach is essential for patient selection and management, to support children and families, to achieve functional improvement and alleviate the overall disease burden for patients and caregivers.

Physiological levels of folic acid reveal purine alterations in Lesch-Nyhan disease

Lesch-Nyhan disease (LND), caused by a deficient salvage purine pathway, is characterized by severe neurological manifestations and uric acid overproduction. However, uric acid is not responsible for brain dysfunction, and it has been suggested that purine nucleotide depletion, or accumulation of other toxic purine intermediates, could be more relevant. Here we show that purine alterations in LND fibroblasts depend on the level of folic acid in the culture media. Thus, physiological levels of folic acid induce accumulation of 5-aminoimidazole-4-carboxamide riboside 5'-monophosphate (ZMP), an intermediary of de novo purine biosynthetic pathway, and depletion of ATP. Additionally, Z-nucleotide derivatives (AICAr, AICA) are detected at high levels in the urine of patients with LND and its variants (hypoxanthine-guanine phosphoribosyltransferase [HGprt]-related neurological dysfunction and HGprt-related hyperuricemia), and the ratio of AICAr/AICA is significantly increased in patients with neurological problems (LND and HGprt-related neurological dysfunction). Moreover, AICAr is present in the cerebrospinal fluid of patients with LND, but not in control individuals. We hypothesize that purine alterations detected in LND fibroblasts may also occur in the brain of patients with LND.

HPRT-related hyperuricemia with a novel p.V35M mutation in HPRT1 presenting familial juvenile gout

Unlike complete deficiency of hypoxanthine phosphoribosyltransferase (HPRT) (i.e., Lesch-Nyhan syndrome), partial HPRT deficiency causes HPRT-related hyperuricemia without neurological symptoms. Herein, we describe a 22-year-old man without neurological symptoms that presented gout, hyperuricemia (serum urate level, 12.2 mg/dL), multiple renal microcalculi, and a family history of juvenile gout that was exhibited by his brother and grandfather. Genetic testing revealed a novel missense mutation, c.103G>A (p.V35M), in the HPRT1 gene, and biochemical testing (conducted using the patient's erythrocytes) showed that the patient retained only 12.4% HPRT enzymatic activity compared to that exhibited by a healthy control subject. We thus diagnosed the patient with HPRT-related hyperuricemia caused by partial HPRT deficiency. After his serum urate level was controlled via treatment with febuxostat, his gout did not recur. Thus, this study emphasizes that HPRT deficiency should be considered as a potential cause of familial juvenile gout, even in the absence of neurological symptoms.

The Dystonias

PURPOSE OF REVIEW

This article provides a summary of the state of the art in the diagnosis, classification, etiologies, and treatment of dystonia.

RECENT FINDINGS

Although many different clinical manifestations of dystonia have been recognized for decades, it is only in the past 5 years that a broadly accepted approach has emerged for classifying them into specific subgroups. The new classification system aids clinical recognition and diagnosis by focusing on key clinical features that help distinguish the many subtypes. In the past few years, major advances have been made in the discovery of new genes as well as advances in our understanding of the biological processes involved. These advances have led to major changes in strategies for diagnosis of the inherited dystonias. An emerging trend is to move away from heavy reliance on the phenotype to target diagnostic testing toward a broader approach that involves large gene panels or whole exome sequencing.

SUMMARY

The dystonias are a large family of phenotypically and etiologically diverse disorders. The diagnosis of these disorders depends on clinical recognition of characteristic clinical features. Symptomatic treatments are useful for all forms of dystonia and include oral medications, botulinum toxins, and surgical procedures. Determination of etiology is becoming increasingly important because the number of disorders is growing and more specific and sometimes disease-modifying therapies now exist.

Phenotypic and molecular spectrum of Korean patients with Lesch-Nyhan syndrome and attenuated clinical variants

Lesch-Nyhan syndrome (LNS) is an X-linked recessive disorder caused by mutations in the HPRT1 gene. The clinical features and mutation spectrum of 26 Korean LNS patients from 23 unrelated families were retrospectively reviewed. The HPRT1 gene was analyzed by direct sequencing of genomic DNA. The median age at diagnosis was 2.3 years (range, 4 months-22.6 years) and the initial presenting features included developmental delay, orange colored urine, and self-injurious behaviors. Most patients were wheelchair-bound and suffered from urinary complications and neurologic problems such as self-mutilation and developmental delay. Twenty different mutations in HPRT1 were identified among 23 independent pedigrees, including six novel mutations. The most common mutation type was truncating mutations including nonsense and frameshift mutations (45%). Large deletions in the HPRT1 gene were identified in exon 1, exons 5-6, exons 1-9, and at chr X:134,459,540-134,467,241 (7702 bp) including the 5'-untranslated region, exon 1, and a portion of intron 1. In conclusion, this study describes the phenotypic spectrum of LNS and has identified 20 mutations from 23 Korean families, including six novel mutations in Korean patients with LNS.

Naming Genes for Dystonia: DYT-z or Ditzy?

Dystonias are a clinically and etiologically diverse group of disorders. Numerous genes have now been associated with different dystonia syndromes, and multiple strategies have been proposed for how these genes should be lumped and split into meaningful categories. The traditional approach has been based on the Human Genome Organization’s plan for naming genetic loci for all disorders. For dystonia this involves a DYT prefix followed by a number (e.g., DYT1, DYT2, DYT3, etc.). A more recently proposed approach involves assigning multiple prefixes according to the main elements of the phenotype (e.g., DYT, PARK, CHOR, TREM, etc.) followed by the name of the responsible gene. This article describes these nomenclature systems and summarizes some of their limitations. We focus on dystonia as an example, although the concepts may be applied to all movement disorders.

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.

Understanding the structure-function relationship of HPRT1 missense mutations in association with Lesch-Nyhan disease and HPRT1-related gout by in silico mutational analysis

The nucleotide salvage pathway is used to recycle degraded nucleotides (purines and pyrimidines); one of the enzymes that helps to recycle purines is hypoxanthine guanine phosphoribosyl transferase 1 (HGPRT1). Therefore, defects in this enzyme lead to the accumulation of DNA and nucleotide lesions and hence replication errors and genetic disorders. Missense mutations in hypoxanthine phosphoribosyl transferase 1 (HPRT1) are associated with deficiencies such as Lesch-Nyhan disease and chronic gout, which have manifestations such as arthritis, neurodegeneration, and cognitive disorders. In the present study, we collected 88 non-synonymous single nucleotide polymorphisms (nsSNPs) from the UniProt, dbSNP, ExAC, and ClinVar databases. We used a series of sequence-based and structure-based in silico tools to prioritize and characterize the most pathogenic and stabilizing or destabilizing nsSNPs. Moreover, to obtain the structural impact of the pathogenic mutations, we mapped the mutations to the crystal structure of the HPRT protein. We further subjected these mutant proteins to a 50 ns molecular dynamics simulation (MDS). The MDS trajectory showed that all mutant proteins altered the structural conformation and dynamic behavior of the HPRT protein and corroborated its association with LND and gout. This study provides essential information regarding the use of HPRT protein mutants as potential targets for therapeutic development.

Inhibiting PNP for the therapy of hyperuricemia in Lesch-Nyhan disease: Preliminary in vitro studies with analogues of immucillin-G

Lesch-Nyhan disease (LND) is a rare X-linked genetic disorder, with complete hypoxanthine-guanine phosphoribosyltransferase (HGPRT) deficiency, uric acid (UA), hypoxanthine and xanthine accumulation, and a devastating neurologic syndrome. UA excess, causing renal failure, is commonly decreased by xanthine oxidoreductase (XOR) inhibitors, such as allopurinol, yielding a xanthine and hypoxanthine increase. Xanthine accumulation may result in renal stones, while hypoxanthine excess seems involved in the neurological disorder. Inhibition of purine nucleoside phosphorylase (PNP) represents a different strategy for lowering urate. PNP catalyzes the cleavage of purine ribo- and d-ribo-nucleosides into ribose/deoxyribose phosphate and free bases, starting catabolism to uric acid. Clinical trials demonstrated that PNP inhibitors, initially developed as anticancer drugs, lowered UA in some gouty patients, in association or not with allopurinol. The present study tested the reliability of an analogue of immucillin-G (C1a), a PNP inhibitor, as a therapy for urate, hypoxanthine, and xanthine excess in LND patients by blocking hypoxanthine production upstream. The therapeutic aim is to limit the administration of XOR inhibitors to LND patients by supplying the PNP inhibitor in low doses, avoiding d-nucleoside toxicity. We report studies conducted in primary cultures of skin fibroblasts from controls and LND patients grown in the presence of the PNP inhibitor. Cell viability, oxypurine release in culture medium, and endocellular nucleotide pattern have been monitored in different growth conditions (inhibitor concentration, time, added inosine). Our results demonstrate effective PNP inhibition by low inhibitor concentration, with reduced hypoxanthine release, and no appreciable toxicity in control or patient cells, suggesting a new therapeutic strategy for LND hyperuricemia.

Macrocytic anemia in Lesch-Nyhan disease and its variants

Purpose

Lesch-Nyhan disease (LND) is an inherited metabolic disorder characterized by overproduction of uric acid and neurobehavioral abnormalities. The purpose of this study is to describe macrocytic erythrocytes as another common aspect of the phenotype.

Methods

Results of 257 complete blood counts (CBC) from a total of 65 patients over a 23-year period were collected from two reference centers where many patients are seen regularly.

Results

Macrocytic erythrocytes occurred in 81–92% of subjects with LND or its neurological variants. After excluding cases with iron deficiency because it might pseudo-normalize erythrocyte volumes, macrocytosis occurred in 97% of subjects. Macrocytic erythrocytes were sometimes accompanied by mild anemia, and rarely by severe anemia.

Conclusions

These results establish macrocytic erythrocytes as very common aspect of the clinical phenotype of LND and its neurological variants. Macrocytosis is so characteristic that its absence should prompt suspicion for some secondary process, such as iron deficiency. Because macrocytosis is uncommon in normal children, it can also be used as a clue for early diagnosis in children with neurodevelopmental delay. Better recognition of this characteristic feature of the disorder will also help to prevent unnecessary diagnostic testing and unnecessary attempts to treat it with folate or B12 supplements.

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.

Cognition in childhood dystonia: a systematic review

AIM

Cognitive impairments have been established as part of the non-motor phenomenology of adult dystonia. In childhood dystonia, the extent of cognitive impairments is less clear. This systematic review aims to present an overview of the existing literature to elucidate the cognitive profile of primary and secondary childhood dystonia.

METHOD

Studies focusing on cognition in childhood dystonia were searched in MEDLINE and PsychInfo up to October 2017. We included studies on idiopathic and genetic forms of dystonia as well as dystonia secondary to cerebral palsy and inborn errors of metabolism.

RESULTS

Thirty-four studies of the initial 527 were included. Studies for primary dystonia showed intact cognition and IQ, but mild working memory and processing speed deficits. Studies on secondary dystonia showed more pronounced cognitive deficits and lower IQ scores with frequent intellectual disability. Data are missing for attention, language, and executive functioning.

INTERPRETATION

This systematic review shows possible cognitive impairments in childhood dystonia. The severity of cognitive impairment seems to intensify with increasing neurological abnormalities. However, the available data on cognition in childhood dystonia are very limited and not all domains have been investigated yet. This underlines the need for future research using standardized neuropsychological procedures in this group.

WHAT THIS PAPER ADDS

There is limited data on cognition in childhood dystonia. Primary dystonia showed intact cognition and IQ, but mild working memory and processing speed deficits. Secondary dystonia showed more pronounced deficits and lower IQ, with frequent intellectual disability. There is a strong need for case-control studies assessing cognition using standardized neuropsychological tests.

Unapparent hypoxanthine-guanine phosphoribosyltransferase deficiency

Complete deficiency of hypoxanthine-guanine phosphoribosyltransferase (HPRT) activity causes Lesch Nyhan disease (LND), characterized by hyperuricemia, severe action dystonia, choreoathetosis, ballismus, cognitive and attention deficit and self-injurious behavior. Partial HPRT deficiency is present in patients with Lesch-Nyhan variant (LNV), who present with HPRT-related gout and a variable degree of neurological involvement. The diagnosis of HPRT deficiency relies on clinical, biochemical, enzymatic and molecular data. Patients with HPRT deficiency present low or undetectable HPRT activity in hemolysates, with increased adenine phosphoribosyltransferase (APRT) activity. We present a 9-year-old boy who experienced an episode of macroscopic hematuria with dysuria and left flank pain. He presented hyperuricemia and hyperuricosuria. HPRT and APRT activities were both normal in hemolysate; however, HPRT activity assayed in intact erythrocytes was 50% of control levels. A new missense point mutation c.424 A>G (T142A) was found in the HPRT1 gene. The apparent Michaelis constant (Km) for 5-phosphoribosyl-pyrophosphate assayed in patient hemolysate was 20-fold of control levels. In conclusion, we report a patient with HPRT deficiency who presented with both normal HPRT and APRT activity in hemolysate, in which the enzyme activity determined in intact erythrocytes was of diagnostic utility.

Severe Respiratory Acidosis in Status Epilepticus as a Possible Etiology of Sudden Death in Lesch-Nyhan Disease: A Case Report and Review of the Literature

INTRODUCTION

Lesch-Nyhan disease (LND) is an X-linked disorder of purine metabolism, associated with self-mutilation, dystonia, and chorea. Seizures are uncommon in LND. Patients with LND are at risk for sudden and unexpected death. The etiology of this is unknown, but appears to occur from a respiratory process. We propose that respiratory failure secondary to subclinical seizure may lead to sudden death in these patients.

CASE

We report a case of an 11-year-old boy with LND who had two episodes of nocturnal gasping. The second event was immediately followed by a 10 min generalized seizure. Upon arrival at the hospital, an arterial blood gas test revealed a severe respiratory acidosis. Following aggressive treatment of his seizures, this patient did well, and was discharged home on oxcarbazepine with rectal diazepam. No further seizures have been noted in 1 year of follow-up.

CONCLUSIONS

In this case report and review, we hypothesize that sudden death from respiratory failure in Lesch-Nyhan disease may in some cases be due to seizure-induced respiratory failure, akin to sudden unexpected death in epilepsy (SUDEP). We suggest screening for paroxysmal respiratory events; consideration of electroencephalography for patients with LND presenting in respiratory distress or failure; and consideration of more aggressive treatment of seizures in these patients. Brief Summary:We present an 11-year-old boy with Lesch-Nyhan disease (LND) who developed respiratory failure and severe respiratory acidosis from his first known seizure, which evolved to subclinical status epilepticus. We propose that patients with LND have a predisposition to respiratory failure and sudden death, which in some cases may be provoked by seizure (sudden unexpected death in epilepsy, or SUDEP).

Novel mutation in HPRT1 causing a splicing error with multiple variations

Lesch-Nyhan disease (LND) is a rare X-linked recessive disorder caused by deficiency of the purine salvage enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT), encoded by the HPRT1. To date, nearly all types of mutations have been reported in the whole gene; however, duplication mutations are rare. We here report the case of a 9-month-old boy with LND. He showed developmental delay, athetosis, and dystonic posture from early infancy, but no self-injurious behaviors. Hyperuricemia was detected, and his HPRT enzyme activity in erythrocytes was completely deficient. A novel duplication mutation (c.372dupT, c.372_374 TTT > c.372_375 TTTT) was identified in exon 4 of the HPRT1, which causes aberrant splicing. This is the third case of a duplication mutation in the HPRT1 that causes splicing error.

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.

The Effect of S-Adenosylmethionine on Self-Mutilation in a Patient with Lesch-Nyhan Disease

BACKGROUND

Lesch-Nyhan disease (LND) is an X-chromosomal disorder of purine metabolism characterized by hyperuricemia, dystonia, and self-mutilation, leading to an extremely high burden of disease in affected patients and families. Although allopurinol therapy can control hyperuricemia, it has no effect on self-mutilation and neurological symptoms. Single reports describe a beneficial effect of S-adenosylmethionine (SAM) on the neurological symptoms, which motivated us to evaluate this alternative treatment.

METHODS

We performed a double-blind placebo-controlled trial to analyze the effects of SAM on self-mutilation attempts in a male patient affected by LND. The trial lasted for 282 days and comprised three alternating verum and placebo periods of 50 days each. The mother of the patient recorded attempts of self-mutilation during the entire trial.

RESULTS

While verum and placebo were both well tolerated, a total of 1,762 events of self-mutilation were recorded, of which 1,281 events were in the placebo period and 481 in the verum period. The daily mean of events was 8.6 with placebo and 4.5 with SAM corresponding to a 50 % decrease in self-mutilation events under SAM treatment (p < 0.05).

CONCLUSION

The results of this double-blind placebo-controlled single-case trial suggest that SAM can have a beneficial effect on self-mutilation in patients with LND, possibly by replenishing the purine pool in affected brain cells.

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.

Potential mechanisms for low uric acid in Parkinson disease

Several epidemiologic studies have described an association between low serum uric acid (UA) and Parkinson disease (PD). Uric acid is a known antioxidant, and one proposed mechanism of neurodegeneration in PD is oxidative damage of dopamine neurons. However, other complex metabolic pathways may contribute. The purpose of this study is to elucidate potential mechanisms of low serum UA in PD. Subjects who met diagnostic criteria for definite or probable PD (n = 20) and controls (n = 20) aged 55-80 years were recruited. Twenty-four hour urine samples were collected from all participants, and both uric acid and allantoin were measured and corrected for body mass index (BMI). Urinary metabolites were compared using a twoway ANOVA with diagnosis and sex as the explanatory variables. There were no significant differences between PD and controls for total UA (p = 0.60), UA corrected for BMI (p = 0.37), or in the interaction of diagnosis and sex on UA (p = 0.24). Similarly, there were no significant differences between PD and controls for allantoin (p = 0.47), allantoin corrected for BMI (p = 0.57), or in the interaction of diagnosis and sex on allantoin (p = 0.78). Allantoin/UA ratios also did not significantly differ by diagnosis (p = 0.99). Our results imply that low serum UA in PD may be due to an intrinsic mechanism that alters the homeostatic set point for serum UA in PD, and may contribute to relatively lower protection against oxidative damage. These findings provide indirect support for neuroprotection trials aimed at raising serum UA.

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.

Protracted late infantile ceroid lipofuscinosis due to TPP1 mutations: Clinical, molecular and biochemical characterization in three sibs

OBJECTIVE

This work investigated the molecular cause responsible for a late-onset parkinsonism-dystonia phenotype in three Italian siblings, and clinically characterize this condition.

METHODS

Extensive neurophysiological and neuroradiological exams were performed on the three sibs. Most frequent late-onset metabolic diseases were ruled out through laboratory and biochemical analyses. A whole exome sequencing (WES) approach was used to identify the molecular cause underlying this condition.

RESULTS AND CONCLUSIONS

Peculiar neurologic phenotype was characterized by dystonia-parkinsonism, cognitive impairment, gait ataxia and apraxia, pyramidal signs. WES analysis allowed the identification of a compound heterozygosity for two nucleotide substitutions (c.1340G>A, p.R447H; c.790C>T, p.Q264X) affecting the TPP1 gene in the three affected siblings. Biochemical analyses demonstrated abrogated TPP1 catalytic activity in primary skin fibroblasts, but revealed residual activity in leukocytes. Our findings document that late infantile neuronal ceroid lipofuscinosis (CLN2), which is caused by TPP1 gene mutations, should be considered in the differential diagnosis of autosomal recessive dystonia-parkinsonism syndromes. The availability of enzyme replacement therapy and other therapeutic approaches for ceroid lipofuscinoses emphasizes the value of reaching an early diagnosis in patients with atypical and milder presentation of these disorders.

Nucleotide salvage deficiencies, DNA damage and neurodegeneration

Nucleotide balance is critically important not only in replicating cells but also in quiescent cells. This is especially true in the nervous system, where there is a high demand for adenosine triphosphate (ATP) produced from mitochondria. Mitochondria are particularly prone to oxidative stress-associated DNA damage because nucleotide imbalance can lead to mitochondrial depletion due to low replication fidelity. Failure to maintain nucleotide balance due to genetic defects can result in infantile death; however there is great variability in clinical presentation for particular diseases. This review compares genetic diseases that result from defects in specific nucleotide salvage enzymes and a signaling kinase that activates nucleotide salvage after DNA damage exposure. These diseases include Lesch-Nyhan syndrome, mitochondrial depletion syndromes, and ataxia telangiectasia. Although treatment options are available to palliate symptoms of these diseases, there is no cure. The conclusions drawn from this review include the critical role of guanine nucleotides in preventing neurodegeneration, the limitations of animals as disease models, and the need to further understand nucleotide imbalances in treatment regimens. Such knowledge will hopefully guide future studies into clinical therapies for genetic diseases.

Hypoxanthine guanine phosphoribosyltransferase (HPRT) deficiencies: HPRT1 mutations in new Japanese families and PRPP concentration

Mutation of hypoxanthine guanine phosphoribosyltransferase (HPRT) gives rise to Lesch-Nyhan syndrome, which is characterized by hyperuricemia, severe motor disability, and self-injurious behavior, or HPRT-related gout with hyperuricemia. Four mutations were detected in two Lesch-Nyhan families and two families with partial deficiency since our last report. A new mutation of G to TT (c.456delGinsTT) resulting in a frameshift (p.Q152Hfs*3) in exon 3 has been identified in one Lesch-Nyhan family. In the other Lesch-Nyhan family, a new point mutation in intron 7 (c.532+5G>T) causing splicing error (exon 7 excluded, p.L163Cfs*4) was detected. In the two partial deficiency cases with hyperuricemia, two missense mutations of p.D20V (c.59A>T) and p.H60R (c.179A>G) were found. An increase of erythrocyte PRPP concentration was observed in the respective phenotypes and seems to be correlated with disease severity.

HPRT deficiency in Spain: what have we learned in the past 30 years (1984-2013)?

Since 1984, we have diagnosed at the La Paz University Hospital, Madrid, Spain, 41 patients with hypoxanthine phosphoribosyltransferase (HPRT) activity deficiency. These patients belonged to 34 families. We have also performed molecular and enzymatic diagnosis in three patients from India, one from Belgium, and three from Colombia. About 1/3 of these patients were followed up at La Paz University Hospital at least every year. This fact has allowed us to examine the complete spectrum of HPRT deficiency as well as to perform a more accurate diagnosis and treatment. In the present review, we also summarized our studies on the basis of physiopathology of the neurological manifestation of Lesch Nyhan disease (LND).

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.