Efficacy and safety of allopurinol in patients with hypoxanthine-guanine phosphoribosyltransferase deficiency

Management of hypertension addressing hyperuricaemia: introduction of nano-based approaches

Uric acid (UA) levels in blood serum have been associated with hypertension, indicating a potential causal relationship between high serum UA levels and the progression of hypertension. Therefore, the reduction of serum UA level is considered a potential strategy for lowering and mitigating blood pressure. If an individual is at risk of developing or already manifesting elevated blood pressure, this intervention could be an integral part of a comprehensive treatment plan. By addressing hyperuricaemia, practitioners may subsidize the optimization of blood pressure regulation, which illustrates the importance of addressing UA levels as a valuable strategy within the broader context of hypertension management. In this analysis, we outlined the operational principles of effective xanthine oxidase inhibitors for the treatment of hyperuricaemia and hypertension, along with an exploration of the contribution of nanotechnology to this field.

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.

Allopurinol Disrupts Purine Metabolism to Increase Damage in Experimental Colitis

Inflammatory bowel disease (IBD) is marked by a state of chronic energy deficiency that limits gut tissue wound healing. This energy shortfall is partially due to microbiota dysbiosis, resulting in the loss of microbiota-derived metabolites, which the epithelium relies on for energy procurement. The role of microbiota-sourced purines, such as hypoxanthine, as substrates salvaged by the colonic epithelium for nucleotide biogenesis and energy balance, has recently been appreciated for homeostasis and wound healing. Allopurinol, a synthetic hypoxanthine isomer commonly prescribed to treat excess uric acid in the blood, inhibits the degradation of hypoxanthine by xanthine oxidase, but also inhibits purine salvage. Although the use of allopurinol is common, studies regarding how allopurinol influences the gastrointestinal tract during colitis are largely nonexistent. In this work, a series of in vitro and in vivo experiments were performed to dissect the relationship between allopurinol, allopurinol metabolites, and colonic epithelial metabolism and function in health and during disease. Of particular significance, the in vivo investigation identified that a therapeutically relevant allopurinol dose shifts adenylate and creatine metabolism, leading to AMPK dysregulation and disrupted proliferation to attenuate wound healing and increased tissue damage in murine experimental colitis. Collectively, these findings underscore the importance of purine salvage on cellular metabolism and gut health in the context of IBD and provide insight regarding the use of allopurinol in patients with IBD.

PAICS as a potential target for cancer therapy linking purine biosynthesis to cancer progression

Tumor cells are required to undergo metabolic reprogramming for rapid development and progression, and one of the metabolic characteristics of cancer cells is the excessive synthesis and utilization of nucleotides. Abnormally increased nucleotides and their metabolites not only directly accelerate tumor cell progression but also indirectly act on stromal cells in the tumor microenvironment (TME) via a paracrine manner to regulate tumor progression. Purine nucleotides are mainly produced via de novo nucleotide synthesis in tumor cells; therefore, intervening in their synthesis has emerged as a promising strategy in anti-tumor therapy. De novo purine synthesis is a 10-step reaction catalyzed by six enzymes to synthesize inosine 5-monophosphate (IMP) and subsequently synthesize AMP and GMP. Phosphoribosylaminoimidazole carboxylase/phosphori-bosylaminoimidazole succinocarboxamide synthetase (PAICS) is a bifunctional enzyme that catalyzes de novo purine synthesis. Aberrantly elevated PAICS expression in various tumors is associated with poor prognosis. Evidence suggests that PAICS and its catalytic product, N-succinylcarboxamide-5-aminoimidazole ribonucleotide (SAICAR), could inhibit tumor cell apoptosis and promote the growth, epithelial-mesenchymal transition (EMT), invasion, and metastasis by regulating signaling pathways such as pyruvate kinase M2 (PKM2), extracellular signal-related kinases 1 and 2 (ERK1/2), focal adhesion kinase (FAK) and so on. This review summarizes the structure, biological functions and the molecular mechanisms of PAICS in cancer development and discusses its potential to be a target for tumor therapy.

Inborn Errors of Purine Salvage and Catabolism

Cellular purine nucleotides derive mainly from de novo synthesis or nucleic acid turnover and, only marginally, from dietary intake. They are subjected to catabolism, eventually forming uric acid in humans, while bases and nucleosides may be converted back to nucleotides through the salvage pathways. Inborn errors of the purine salvage pathway and catabolism have been described by several researchers and are usually referred to as rare diseases. Since purine compounds play a fundamental role, it is not surprising that their dysmetabolism is accompanied by devastating symptoms. Nevertheless, some of these manifestations are unexpected and, so far, have no explanation or therapy. Herein, we describe several known inborn errors of purine metabolism, highlighting their unexplained pathological aspects. Our intent is to offer new points of view on this topic and suggest diagnostic tools that may possibly indicate to clinicians that the inborn errors of purine metabolism may not be very rare diseases after all.

Recurrent Xanthine Stones in a Young Patient with Lesch-Nyhan Syndrome

Background: Lesch-Nyhan syndrome results from a rare X-linked inborn error of metabolism leading to a total body accumulation of uric acid. Clinical manifestations include self-mutilating behavior, poor muscle control, intellectual disability, gout, and kidney disease. Unfortunately, life expectancy is limited to the second or third decade of life because of symptoms associated with hyperuricemia, particularly renal failure. Patients with this condition frequently necessitate urologic intervention as the buildup of lithogenic substances predispose individuals to the development of kidney and bladder stones. Case Presentation: We present the case of a 23-year-old white man with known Lesch-Nyhan syndrome and recurrent bilateral xanthine stones despite repeated urologic interventions. Conclusion: Therapy for Lesch-Nyhan syndrome consists of reduction of uric acid achieved through allopurinol. However, excess allopurinol dosing can lead to development of xanthine kidney and bladder stones. Thus, the treating clinician must maintain a delicate balance between managing hyperuricemia and avoiding xanthine urolithiasis.

Late diagnosis of Lesch-Nyhan disease complicated with end-stage renal disease and tophi burst: a case report

Background

Lesch–Nyhan disease (LND) is a rare X-linked recessive inborn error of purine metabolism. Late diagnosis of LND may cause significant morbidity. LND cases have never been reported in Indonesia.

Case report

A 15-year-old male who had been diagnosed with cerebral palsy was referred to our hospital due to renal failure requiring emergency dialysis. The patient presented with three classic manifestations of LND: increased uric acid levels, neurological disorders, and self-injurious behaviors. LND was suspected because of an abscess-like lump on the left ankle that was confirmed to be a tophus, which had burst and discharged thick masses containing blood, debris, and white crystal materials. The diagnosis of LND was confirmed by the presence of a deletion to exon 1 of the HPRT1 gene. The patient received oral allopurinol daily and treatment for end-stage renal disease (ESRD), which included regular dialysis and subcutaneous administration of erythropoietin. At a 2-month follow-up, he improved clinically with a 71% decrease in uric acid levels after regular dialysis and allopurinol treatment.

Conclusion

In developed countries, LND can be diagnosed as early as 3 days after birth. However, diagnosis in the present case was delayed due to the rarity of the disease and the limited number of facilities in Indonesia that offer genetic counseling. Late diagnosis of LND leads to ESRD and irreversible abnormalities. This is the first case of LND presenting with a unique clinical presentation of tophus burst reported in Indonesia.

Drug-Induced Urolithiasis in Pediatric Patients

Drug-induced nephrolithiasis is a rare condition in children. The involved drugs may be divided into two different categories according to the mechanism involved in calculi formation. The first one includes poorly soluble drugs that favor the crystallization and calculi formation. The second category includes drugs that enhance calculi formation through their metabolic effects. The diagnosis of these specific calculi depends on a detailed medical history, associated comorbidities and the patient's history of drug consumption. There are several risk factors associated with drug-induced stones, such as high dose of consumed drugs and long duration of treatment. Moreover, there are some specific risk factors, including urinary pH and the amount of fluid consumed by children. There are limited data regarding pediatric lithogenic drugs, and hence, our aim was to perform a comprehensive review of the literature to summarize these drugs and identify the possible mechanisms involved in calculi formation and discuss the management and preventive measures for these calculi.

Hyperuricemia in Children and Adolescents: Present Knowledge and Future Directions

Recent evidence suggests that hyperuricemia is an important condition in children and adolescents, particularly in association with noncommunicable diseases. This review aims to summarize our current understanding of this condition in pediatric patients. An analysis of serum uric acid reference values in a healthy population indicates that they increase gradually with age until adolescence, with differences between the sexes arising at about 12 years of age. This information should be taken into consideration when defining hyperuricemia in studies. Gout is extremely rare in children and adolescents, and most patients with gout have an underlying disease. The major causes of hyperuricemia are chronic conditions, including Down syndrome, metabolic or genetic disease, and congenital heart disease, and acute conditions, including gastroenteritis, bronchial asthma (hypoxia), malignant disorders, and drug side effects. The mechanisms underlying the associations between these diseases and hyperuricemia are discussed, together with recent genetic information. Obesity is a major cause of hyperuricemia in otherwise healthy children and adolescents. Obesity is often accompanied by metabolic syndrome; hyperuricemia in obese children and adolescents is associated with the components of metabolic syndrome and noncommunicable diseases, including hypertension, insulin resistance, dyslipidemia, and chronic kidney disease. Finally, strategies for the treatment of hyperuricemia, including lifestyle intervention and drug administration, are presented.

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.

Diatom Allantoin Synthase Provides Structural Insights into Natural Fusion Protein Therapeutics

Humans have lost the ability to convert urate into the more soluble allantoin with the evolutionary inactivation of three enzymes of the uricolytic pathway. Restoration of this function through enzyme replacement therapy can treat severe hyperuricemia and Lesch-Nyhan disease. Through a genomic exploration of natural gene fusions, we found that plants and diatoms independently evolved a fusion protein (allantoin synthase) complementing two human pseudogenes. The 1.85-Å-resolution crystal structure of allantoin synthase from the diatom Phaeodactylum tricornutum provides a rationale for the domain combinations observed in the metabolic pathway, suggesting that quaternary structure is key to the evolutionary success of protein domain fusions. Polyethylene glycol (PEG) conjugation experiments indicate that a PEG-modified form of the natural fusion protein provides advantages over separate enzymes in terms of activity maintenance and manufacturing of the bioconjugate. These results suggest that the combination of different activities in a single molecular unit can simplify the production and chemical modification of recombinant proteins for multifunctional enzyme therapy.

Xanthine calculi in a patient with Lesch-Nyhan syndrome and factor V Leiden treated with allopurinol: case report

Background

Lesch-Nyhan syndrome is a rare inborn error of purine metabolism marked by a complete deficiency of the enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT). Inherited as an X-linked recessive genetic disorder that primarily affects males, patients with Lesch-Nyhan syndrome exhibit severe neurological impairments, including choreoathetosis, ballismus, cognitive dysfunction, and self-injurious behavior. Uric acid levels are usually abnormally high, leading to kidney and bladder stones which often necessitate urological intervention. Factor V Leiden is an autosomal dominant disorder of blood clotting associated with hypercoagulability, thrombophilia, and renal disease.

Case presentation

We present the first reported case of xanthine calculi in a patient with Lesch-Nyhan syndrome and Factor V Leiden who was treated with allopurinol. A renal ultrasound and CT scan demonstrated bilateral staghorn calculi in the kidneys as well as nephrocalcinosis. Two years earlier the patient underwent cystoscopy with bilateral ureteroscopy and laser lithotripsy, and he was stone free afterwards. The patient subsequently underwent bilateral percutaneous nephrolithotomy (PCNL) and was stone free following the procedure. Patients with endogenous overproduction of uric acid who are being treated with allopurinol have a higher chance of developing xanthine stones.

Conclusions

Pediatricians treating these children should be aware of these rare conditions and promptly manage the potential complications that may require medical or surgical intervention.

Drug-Induced Kidney Stones and Crystalline Nephropathy: Pathophysiology, Prevention and Treatment

Drug-induced calculi represent 1-2% of all renal calculi. The drugs reported to produce calculi may be divided into two groups. The first one includes poorly soluble drugs with high urine excretion that favour crystallisation in the urine. Among them, drugs used for the treatment of patients with human immunodeficiency, namely atazanavir and other protease inhibitors, and sulphadiazine used for the treatment of cerebral toxoplasmosis, are the most frequent causes. Besides these drugs, about 20 other molecules may induce nephrolithiasis, such as ceftriaxone or ephedrine-containing preparations in subjects receiving high doses or long-term treatment. Calculi analysis by physical methods including infrared spectroscopy or X-ray diffraction is needed to demonstrate the presence of the drug or its metabolites within the calculi. Some drugs may also provoke heavy intra-tubular crystal precipitation causing acute renal failure. Here, the identification of crystalluria or crystals within the kidney tissue in the case of renal biopsy is of major diagnostic value. The second group includes drugs that provoke the formation of urinary calculi as a consequence of their metabolic effects on urinary pH and/or the excretion of calcium, phosphate, oxalate, citrate, uric acid or other purines. Among such metabolically induced calculi are those formed in patients taking uncontrolled calcium/vitamin D supplements, or being treated with carbonic anhydrase inhibitors such as acetazolamide or topiramate. Here, diagnosis relies on a careful clinical inquiry to differentiate between common calculi and metabolically induced calculi, of which the incidence is probably underestimated. Specific patient-dependent risk factors also exist in relation to urine pH, volume of diuresis and other factors, thus providing a basis for preventive or curative measures against stone formation.

A Trivalent Enzymatic System for Uricolytic Therapy of HPRT Deficiency and Lesch-Nyhan Disease

PURPOSE

Because of the evolutionary loss of the uricolytic pathway, humans accumulate poorly soluble urate as the final product of purine catabolism. Restoration of uricolysis through enzyme therapy is a promising treatment for severe hyperuricemia caused by deficiency of hypoxanthine-guanine phosphoribosyltransferase (HPRT). To this end, we studied the effect of PEG conjugation on the activity and stability of the enzymatic complement required for conversion of urate into the more soluble (S)-allantoin.

METHODS

We produced in recombinant form three zebrafish enzymes required in the uricolytic pathway. We carried out a systematic study of the effect of PEGylation on the function and stability of the three enzymes by varying PEG length, chemistry and degree of conjugation. We assayed in vitro the uricolytic activity of the PEGylated enzymatic triad.

RESULTS

We defined conditions that allow PEGylated enzymes to retain native-like enzymatic activity even after lyophilization or prolonged storage. A combination of the three enzymes in an appropriate ratio allowed efficient conversion of urate to (S)-allantoin with no accumulation of intermediate metabolites.

CONCLUSIONS

Pharmaceutical restoration of the uricolytic pathway is a viable approach for the treatment of severe hyperuricemia.

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.

Nephrocalcinosis and Renal Failure in Lesch-Nyhan Syndrome: Report of Two Familial Cases and Review of the Literature

Lesch-Nyhan syndrome is an X-linked recessive inborn error of purine metabolism, due to deficiency of the enzyme HPRT (hypoxanthine-guanine phosphoribosyl transferase) and underlying HPRT gene mutations (over 300 mutations identified up to date). It is characterized by a wide range of neurological symptoms and signs (mainly a combination of spastic diplegia with choreoathetosis and an overall psychomotor redardation). Herein, we report of two cousins with Lesch-Nyhan syndrome and a confirmed novel HPRT gene mutation: c.65T>C, who both developed nephrocalcinosis and renal failure, findings not been previously published in children with HPRT deficiency.

Generation of Hprt-disrupted rat through mouse←rat ES chimeras

We established rat embryonic stem (ES) cell lines from a double transgenic rat line which harbours CAG-GFP for ubiquitous expression of GFP in somatic cells and Acr3-EGFP for expression in sperm (green body and green sperm: GBGS rat). By injecting the GBGS rat ES cells into mouse blastocysts and transplanting them into pseudopregnant mice, rat spermatozoa were produced in mouse←rat ES chimeras. Rat spermatozoa from the chimeric testis were able to fertilize eggs by testicular sperm extraction combined with intracytoplasmic sperm injection (TESE-ICSI). In the present paper, we disrupted rat hypoxanthine-guanine phosphoribosyl transferase (Hprt) gene in ES cells and produced a Hprt-disrupted rat line using the mouse←rat ES chimera system. The mouse←rat ES chimera system demonstrated the dual advantages of space conservation and a clear indication of germ line transmission in knockout rat production.

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).

Partial HPRT Deficiency with a Novel Mutation of the HPRT Gene in Combination with Four Previously Reported Variants Associated with Hyperuricemia

A 15-year-old boy was referred to our department due to gout. The laboratory findings showed hyperuricemia with a decreased erythrocyte hypoxanthine phosphoribosyl transferase (HPRT) activity. The HPRT cDNA sequence was revealed to be 206A>T, which has not been previously reported. In addition, direct sequencing of genomic DNA showed the patient to possess four variants reported to be associated with hyperuricemia. This is the first case report of partial HPRT deficiency due to a novel HPRT mutation accompanied by variants associated with hyperuricemia. Combination treatment consisting of benzbromarone and febuxostat had a significant effect in reducing the urate level in our patient.

Inborn errors of purine metabolism: clinical update and therapies

Inborn errors of purine metabolism exhibit broad neurological, immunological, haematological and renal manifestations. Limited awareness of the phenotypic spectrum, the recent descriptions of newer disorders and considerable genetic heterogeneity, have contributed to long diagnostic odysseys for affected individuals. These enzymes are widely but not ubiquitously distributed in human tissues and are crucial for synthesis of essential nucleotides, such as ATP, which form the basis of DNA and RNA, oxidative phosphorylation, signal transduction and a range of molecular synthetic processes. Depletion of nucleotides or accumulation of toxic intermediates contributes to the pathogenesis of these disorders. Maintenance of cellular nucleotides depends on the three aspects of metabolism of purines (and related pyrimidines): de novo synthesis, catabolism and recycling of these metabolites. At present, treatments for the clinically significant defects of the purine pathway are restricted: purine 5'-nucleotidase deficiency with uridine; familial juvenile hyperuricaemic nephropathy (FJHN), adenine phosphoribosyl transferase (APRT) deficiency, hypoxanthine phosphoribosyl transferase (HPRT) deficiency and phosphoribosyl-pyrophosphate synthetase superactivity (PRPS) with allopurinol; adenosine deaminase (ADA) and purine nucleoside phosphorylase (PNP) deficiencies have been treated by bone marrow transplantation (BMT), and ADA deficiency with enzyme replacement with polyethylene glycol (PEG)-ADA, or erythrocyte-encapsulated ADA; myeloadenylate deaminase (MADA) and adenylosuccinate lyase (ADSL) deficiencies have had trials of oral ribose; PRPS, HPRT and adenosine kinase (ADK) deficiencies with S-adenosylmethionine; and molybdenum cofactor deficiency of complementation group A (MOCODA) with cyclic pyranopterin monophosphate (cPMP). In this review we describe the known inborn errors of purine metabolism, their phenotypic presentations, established diagnostic methodology and recognised treatment options.

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.

Normal uricemia in Lesch-Nyhan syndrome and the association with pulmonary embolism in a young child-a case report and literature review

Deficiency of hypoxanthine phosphoribosyltransferase activity is a rare inborn error of purine metabolism with subsequent uric acid overproduction and neurologic presentations. The diagnosis of Lesch-Nyhan syndrome (LNS) is frequently delayed until self-mutilation becomes evident. We report the case of a boy aged 1 year and 10 months who was diagnosed with profound global developmental delay, persistent chorea, and compulsive self-mutilation since the age of 1 year. Serial serum uric acid levels showed normal uric acid level, and the spot urine uric acid/creatinine ratio was >2. The hypoxanthine phosphoribosyltransferase cDNA showed the deletion of exon 6, and the boy was subsequently diagnosed to have LNS. He also had respiratory distress due to pulmonary embolism documented by chest computed tomography scan. This report highlights the need to determine the uric acid/creatinine ratio caused by increased renal clearance in LNS in young children. The presence of pulmonary embolism is unusual and may be the consequence of prolonged immobilization.

Update on the phenotypic spectrum of Lesch-Nyhan disease and its attenuated variants

Congenital deficiency of the enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT) results in a spectrum of clinical phenotypes. All of these phenotypes are associated with marked overproduction of uric acid and related problems such as hyperuricemia, urate nephrolithiasis, tophi, and gout. The mildest phenotypes include only problems related to overproduction of uric acid. The most severe phenotype is known as Lesch-Nyhan disease, in which the phenotype also includes severe motor handicap, intellectual disability, and self-injurious behavior. In between these two extremes is a continuous spectrum of phenotypes with varying degrees of motor and cognitive handicap but no self-injurious behavior. The pathogenesis of overproduction of uric acid in HPRT deficiency is well-understood, and treatments are available to control it. The pathogenesis of the neurobehavioral problems is less well-understood, and effective treatments for them are lacking.

Genetic determinants of urolithiasis

Urolithiasis affects approximately 10% of individuals in Western societies by the seventh decade of life. The most common form, idiopathic calcium oxalate urolithiasis, results from the interaction of multiple genes and their interplay with dietary and environmental factors. To date, considerable progress has been made in identifying the metabolic risk factors that predispose to this complex trait, among which hypercalciuria predominates. The specific genetic and epigenetic factors involved in urolithiasis have remained less clear, partly owing to the candidate gene and linkage methods that have been available until now, being inherently low in their power of resolution and in assessing modest effects in complex traits. However, together with investigations of rare, Mendelian forms of urolithiasis associated with various metabolic risk factors, these methods have afforded insights into biological pathways that seem to underlie the development of stones in the urinary tract. Monogenic diseases account for a greater proportion of stone formers in children and adolescents than in adults. Early diagnosis of monogenic forms of urolithiasis is of importance owing to associated renal injury and other potentially treatable disease manifestations, but diagnosis is often delayed because of a lack of familiarity with these rare disorders. In this Review, we will discuss advances in the understanding of the genetics underlying polygenic and monogenic forms of urolithiasis.

2011 recommendations for the diagnosis and management of gout and hyperuricemia

Gout is a major health problem in the United States; it affects 8.3 million people, which is approximately 4% of the adult population. Gout is most often diagnosed and managed in primary care practices; thus, primary care physicians have a significant opportunity to improve patient outcomes. Following publication of the 2006 European League Against Rheumatism (EULAR) gout guidelines, significant new evidence has accumulated, and new treatments for patients with gout have become available. It is the objective of these 2011 recommendations to update the 2006 EULAR guidelines, paying special attention to the needs of primary care physicians. The revised 2011 recommendations are based on the Grading of Recommendations Assessment, Development, and Evaluation approach as an evidence-based strategy for rating quality of evidence and grading the strength of recommendation formulated for use in clinical practice. A total of 26 key recommendations, 10 for diagnosis and 16 for management, of patients with gout were evaluated, resulting in important updates for patient care. The presence of monosodium urate crystals and/or tophus and response to colchicine have the highest clinical diagnostic value. The key aspect of effective management of an acute gout attack is initiation of treatment within hours of symptom onset. Low-dose colchicine is better tolerated and is as effective as a high dose. When urate-lowering therapy (ULT) is indicated, the xanthine oxidase inhibitors allopurinol and febuxostat are the options of choice. Febuxostat can be prescribed at unchanged doses for patients with mild-to-moderate renal or hepatic impairment. The target of ULT should be a serum uric acid level that is ≤ 6 mg/dL. For patients with refractory and tophaceous gout, intravenous pegloticase is a new treatment option. This article is a summary of the 2011 clinical guidelines published in Postgraduate Medicine. This article provides a streamlined, accessible overview intended for quick review by primary care physicians, with the full guidelines being a resource for those seeking additional background information and expanded discussion.

Nephrolithiasis related to inborn metabolic diseases

Nephrolithiasis associated with inborn metabolic diseases is a very rare condition with some common characteristics: early onset of symptoms, family history, associated tubular impairment, bilateral, multiple and recurrent stones, and association with nephrocalcinosis. The prognosis of such diseases may lead to life threatening conditions, not only because of unabated kidney damage but also because of progressive extra-renal involvement, either in a systemic form (e.g. primary hyperoxaluria type 1, requiring combined liver and kidney transplantation), or in a neurological form (Lesch-Nyhan syndrome leading to auto-mutilation and disability, phosphoribosyl pyrophosphate synthetase superactivity, which is associated with mental retardation). Patients with other inborn metabolic diseases present only with recurrent stone formation, such as cystinuria, adenine phosphoribosyl-transferase deficiency, xanthine deficiency. Finally, nephrolithiasis may be secondarily part of some other metabolic diseases, such as glycogen storage disease type 1 or inborn errors of metabolism leading to Fanconi syndrome (nephropathic cystinosis, tyrosinaemia type 1, fructose intolerance, Wilson disease, respiratory chain disorders, etc.). The diagnosis is based on highly specific investigations, including crystal identification, biochemical analyses and DNA study. The treatment of nephrolithiasis requires hydration as well as specific measures. Compliance is a major issue regarding the progression of renal damage, but the overall outcome mainly depends on extra-renal involvement in relation to the metabolic defect.

Hypoxanthine-guanine phosophoribosyltransferase (HPRT) deficiency: Lesch-Nyhan syndrome

Deficiency of hypoxanthine-guanine phosphoribosyltransferase (HPRT) activity is an inborn error of purine metabolism associated with uric acid overproduction and a continuum spectrum of neurological manifestations depending on the degree of the enzymatic deficiency. The prevalence is estimated at 1/380,000 live births in Canada, and 1/235,000 live births in Spain. Uric acid overproduction is present inall HPRT-deficient patients and is associated with lithiasis and gout. Neurological manifestations include severe action dystonia, choreoathetosis, ballismus, cognitive and attention deficit, and self-injurious behaviour. The most severe forms are known as Lesch-Nyhan syndrome (patients are normal at birth and diagnosis can be accomplished when psychomotor delay becomes apparent). Partial HPRT-deficient patients present these symptoms with a different intensity, and in the least severe forms symptoms may be unapparent. Megaloblastic anaemia is also associated with the disease. Inheritance of HPRT deficiency is X-linked recessive, thus males are generally affected and heterozygous female are carriers (usually asymptomatic). Human HPRT is encoded by a single structural gene on the long arm of the X chromosome at Xq26. To date, more than 300 disease-associated mutations in the HPRT1 gene have been identified. The diagnosis is based on clinical and biochemical findings (hyperuricemia and hyperuricosuria associated with psychomotor delay), and enzymatic (HPRT activity determination in haemolysate, intact erythrocytes or fibroblasts) and molecular tests. Molecular diagnosis allows faster and more accurate carrier and prenatal diagnosis. Prenatal diagnosis can be performed with amniotic cells obtained by amniocentesis at about 15–18 weeks' gestation, or chorionic villus cells obtained at about 10–12 weeks' gestation. Uric acid overproduction can be managed by allopurinol treatment. Doses must be carefully adjusted to avoid xanthine lithiasis. The lack of precise understanding of the neurological dysfunction has precluded development of useful therapies. Spasticity, when present, and dystonia can be managed with benzodiazepines and gamma-aminobutyric acid inhibitors such as baclofen. Physical rehabilitation, including management of dysarthria and dysphagia, special devices to enable hand control, appropriate walking aids, and a programme of posture management to prevent deformities are recommended. Self-injurious behaviour must be managed by a combination of physical restraints, behavioural and pharmaceutical treatments.