Garrod's Croonian Lectures (1908) and the charter 'Inborn Errors of Metabolism': albinism, alkaptonuria, cystinuria, and pentosuria at age 100 in 2008

Bacterial quality of urinary tract in patients with alkaptonuria

BACKGROUND

The aim of the current study was to determine whether there is an association between alkaptonuria (AKU) and urinary tract infection (UTI) by exploring the bacterial quality of the urinary tract, as most of the patients with AKU present with frequent occurrence of urinary tract symptoms such as incomplete emptying of urinary bladder, dysuria and nocturia.

METHODS

Study samples were collected from 22 participants; 9 from patients with AKU, 9 from individuals who were AKU carriers, and 4 people served as control. Confirmation of AKU diagnosis was established by the ferric chloride test and quantitative determination of urinary homogentisic acid (HGA) levels.

RESULTS

In the ferric chloride test, the urine samples of AKU patients showed a characteristic black ring upon addition of few drops of ferric chloride solution. During urinary HGA determination, patients with AKU had increased levels of urinary HGA as compared to carriers and controls. The following 10 bacterial species were isolated from the urinary tract of AKU patients, carriers and controls: Sphingomonas paucimobilis, Escherichia coli, Francisella tularensis, Staphylococcus hominis, Staphylococcus haemolyticus, Leuconostoc mesenteroides, Dermacoccus nishinomiyaensis, Kytococcus sedentarius, Serratia fonticola and Granulicatella adiacens. The presence of S. paucimobilis was found in three male patients, and one female each from the carrier and control groups. Almost all study samples were positive for D. nishinomiyaensis and K. sedentarius. S. fonticola and G. adiacens were found only in AKU carrier females.

CONCLUSIONS

The results deduced that males show symptoms of arthritis early and more severely than females and by this it appears that there is an association between these symptoms and the percentage of bacterial infection in males that requires more accurate diagnosis and treatment to clarify such relationship. In the current study, males (patients, carriers, and controls) were more likely to have bacterial infections than females (64% vs. 36%). The 16 and 2 bacterial isolates, detected in 7 males and 2 females AKU patients, respectively, revealed that male AKU patients had a 2.3-fold greater rate of bacterial infection than female AKU patients. Therefore, further studies are warranted to investigate if there's any relationship between higher incidence of bacterial infections and development of AKU-related clinical symptoms in the male population.

The Awesome Power of Human Genetics of Infectious Disease

Since the identification of sickle cell trait as a heritable form of resistance to malaria, candidate gene studies, linkage analysis paired with sequencing, and genome-wide association (GWA) studies have revealed many examples of genetic resistance and susceptibility to infectious diseases. GWA studies enabled the identification of many common variants associated with small shifts in susceptibility to infectious diseases. This is exemplified by multiple loci associated with leprosy, malaria, HIV, tuberculosis, and coronavirus disease 2019 (COVID-19), which illuminate genetic architecture and implicate pathways underlying pathophysiology. Despite these successes, most of the heritability of infectious diseases remains to be explained. As the field advances, current limitations may be overcome by applying methodological innovations such as cellular GWA studies and phenome-wide association (PheWA) studies as well as by improving methodological rigor with more precise case definitions, deeper phenotyping, increased cohort diversity, and functional validation of candidate loci in the laboratory or human challenge studies.

Estimating heritability of glycaemic response to metformin using nationwide electronic health records and population-sized pedigree

Background

Variability of response to medication is a well-known phenomenon, determined by both environmental and genetic factors. Understanding the heritable component of the response to medication is of great interest but challenging due to several reasons, including small study cohorts and computational limitations.

Methods

Here, we study the heritability of variation in the glycaemic response to metformin, first-line therapeutic agent for type 2 diabetes (T2D), by leveraging 18 years of electronic health records (EHR) data from Israel’s largest healthcare service provider, consisting of over five million patients of diverse ethnicities and socio-economic background. Our cohort consists of 80,788 T2D patients treated with metformin, with an accumulated number of 1,611,591 HbA1C measurements and 4,581,097 metformin prescriptions. We estimate the explained variance of glycated hemoglobin (HbA1c%) reduction due to inheritance by constructing a six-generation population-size pedigree from national registries and linking it to medical health records.

Results

Using Linear Mixed Model-based framework, a common-practice method for heritability estimation, we calculate a heritability measure of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${h}^{2}=12.6 \%$$\end{document}h2=12.6% (95% CI, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$6.1 \%\! -\!19.1 \%$$\end{document}6.1%−19.1%) for absolute reduction of HbA1c% after metformin treatment in the entire cohort, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${h}^{2}=21.0 \%$$\end{document}h2=21.0% (95% CI, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$7.8 \%\! -\!34.4 \%$$\end{document}7.8%−34.4%) for males and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${h}^{2}=22.9 \%$$\end{document}h2=22.9% (95% CI, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$10.0 \%\! -\!35.7 \%$$\end{document}10.0%−35.7%) in females. Results remain unchanged after adjusting for pre-treatment HbA1c%, and in proportional reduction of HbA1c%.

Conclusions

To the best of our knowledge, our work is the first to estimate heritability of drug response using solely EHR data combining a pedigree-based kinship matrix. We demonstrate that while response to metformin treatment has a heritable component, most of the variation is likely due to other factors, further motivating non-genetic analyses aimed at unraveling metformin’s action mechanism.

Individuals in a population might respond differently to the same medication and this phenomenon is commonly attributed to either genes or the environment. Here, we studied the familial aspects of the response to metformin, a medication used in the treatment of type 2 diabetes. We combined information from 18 years of medical records identifying newly treated patients with type 2 diabetes with information about how the trait was inherited within their families. We calculated a metric that tells us how well differences in people’s genes account for differences in their traits, and demonstrate that although the difference in response to metformin is in part explained by the genes people with type 2 diabetes inherit, most of it is not explained by genes. This finding contributes to a better understanding of differences in metformin response and might help inform treatment in future.

Kalka and Gavrieli et al. assessed the heritability of variation in the glycaemic response to metformin by leveraging electronic health records data gathered from a large cohort of patients with diabetes and combining it with pedigree information. The authors show that although the variability in this response has a heritable component, most of it is likely non-genetic.

Developments in evidence creation for treatments of inborn errors of metabolism

Inborn errors of metabolism (IEM) represent the first group of genetic disorders, amenable to causal therapies. In addition to traditional medical diet and cofactor treatments, new treatment strategies such as enzyme replacement and small molecule therapies, solid organ transplantation, and cell-and gene-based therapies have become available. Inherent to the rare nature of the single conditions, generating high-quality evidence for these treatments in clinical trials and under real-world conditions has been challenging. Guidelines developed with standardized methodologies have contributed to improve the practice of care and long-term clinical outcomes. Adaptive trial designs allow for changes in sample size, group allocation and trial duration as the trial proceeds. n-of-1 studies may be used in small sample sized when participants are clinically heterogeneous. Multicenter observational and registry-based clinical trials are promoted via international research networks. Core outcome and standard data element sets will enhance comparative analysis of clinical trials and observational studies. Patient-centered outcome-research as well as patient-led research initiatives will further accelerate the development of therapies for IEM.

Genetic mechanisms of neurodevelopmental disorders

Neurodevelopmental disorders encompass a broad range of conditions, which include autism, epilepsy, and intellectual disability. These disorders are relatively common and have associated clinical and genetic heterogeneity. Technology has driven much of our understanding of these diseases and their genetic underlying mechanisms, particularly highlighted by the study of large cohorts with comparative genomic hybridization and the more recent implementation of next-generation sequencing (NGS). The mapping of copy number variants throughout the genome has highlighted the recurrent, highly penetrant, de novo variation in syndromic forms of neurodevelopmental disease. NGS of affected individuals and their parents led to a dramatic shift in our understanding as these studies showed that a significant proportion of affected individuals carry rare, de novo variants within single genes that explain their disease presentation. Deep sequencing studies further implicate mosaicism as another mechanism of disease. However, it has also become clear that while rare variants explain a significant proportion of sporadic neurodevelopmental disease, rare variation still does not fully account for the familial clustering and high heritability observed. Common variants, including those within these known disease genes, are also shown to contribute significantly to overall risk. There is also increasing awareness of the important contribution of epigenetic factors and gene-environment interactions.

Alkaptonuria – Many questions answered, further challenges beckon

Alkaptonuria is an iconic rare inherited inborn error of metabolism affecting the tyrosine metabolic pathway, resulting in the accumulation of homogentisic acid in the circulation, and significant excretion in urine. Dating as far back as 1500 BC in the Egyptian mummy Harwa, homogentisic acid was shown to be central to the pathophysiology of alkaptonuria through its deposition in collagenous tissues in a process termed ochronosis. Clinical manifestations occurring as a consequence of this are typically observed from the third decade of life, are lifelong and significantly affect the quality of life. In large supportive and palliative treatment measures are available to patients, including analgesia, physiotherapy and joint replacement. Studying the natural history of alkaptonuria, in a murine model and human subjects, has provided key insights into the biochemical and molecular mechanisms underlying the pathophysiology associated with the disease, and has enabled a better understanding of the common disease osteoarthritis. In the last decade, a major focus has been on an unlicensed disease-modifying therapy called nitisinone. This has been shown to be highly efficacious in reducing homogentisic acid, and it is hoped this will halt ochronosis, thus limiting the clinical complications associated with the disease. A well-documented metabolic consequence of nitisinone therapy is hypertyrosinaemia, the clinical implications of which are uncertain. Recent metabolomic studies have helped understand the wider metabolic consequences of nitisinone therapy.

Pharmacogenetics and drug metabolism: historical perspective and appraisal

The events leading up to the discovery of genetically controlled polymorphic metabolism of xenobiotics and pharmaceutical chemicals are briefly summarised with the salient historical features being emphasised. Especial attention has been given to seminal works in the then emerging field.The evolving knowledge of such polymorphic metabolism and its role in the quest for personalised medicine and the individualisation of patient drug therapy are appraised. Opinion is offered as to whether or not the full potential has been exploited and if the practical application of this information may be regarded as a success or failure within the present clinical arena.

Substrate reduction therapy for inborn errors of metabolism

Inborn errors of metabolism (IEM) represent a growing group of monogenic disorders each associated with inherited defects in a metabolic enzyme or regulatory protein, leading to biochemical abnormalities arising from a metabolic block. Despite the well-established genetic linkage, pathophysiology and clinical manifestations for many IEMs, there remains a lack of transformative therapy. The available treatment and management options for a few IEMs are often ineffective or expensive, incurring a significant burden to individual, family, and society. The lack of IEM therapies, in large part, relates to the conceptual challenge that IEMs are loss-of-function defects arising from the defective enzyme, rendering pharmacologic rescue difficult. An emerging approach that holds promise and is the subject of a flurry of pre-/clinical applications, is substrate reduction therapy (SRT). SRT addresses a common IEM phenotype associated with toxic accumulation of substrate from the defective enzyme, by inhibiting the formation of the substrate instead of directly repairing the defective enzyme. This minireview will summarize recent highlights towards the development of emerging SRT, with focussed attention towards repurposing of currently approved drugs, approaches to validate novel targets and screen for hit molecules, as well as emerging advances in gene silencing as a therapeutic modality.

Inherited Metabolic Disorders: Implications for the Obstetrician-Gynecologist

Importance

Inherited metabolic disorders, or inborn errors of metabolism, can result in significant morbidity and mortality. Advances in genetic testing, including newborn screening and prenatal carrier screening, continue to increase awareness and highlight the importance of these conditions. Increasingly, women born with these conditions are surviving to adulthood, and many become pregnant. The practicing obstetrician-gynecologist should be familiar with the most common and the most relevant inherited metabolic disorders affecting women.

Objective

The objective of this review is to define inherited metabolic disorders that have relevance to the obstetrician-gynecologist. We discuss the diagnosis, presentation, epidemiology, and special concerns to the obstetrician-gynecologist managing patients affected by these conditions.

Evidence Acquisition

A MEDLINE search of "inherited metabolic disorders" and "inborn errors of metabolism" and specific conditions reported in the review was performed.

Results

The evidence cited in this review includes 8 case reports or case series, 4 text books, 1 systematic review, 1 American College of Obstetricians and Gynecologists committee opinion, and 18 additional peer-reviewed journal articles that were original research or expert opinion summaries.

Conclusions and Relevance

Inherited metabolic disorders manifest in diverse ways that have clinical implications for the obstetrician-gynecologist. Knowledge of these disorders and their pathophysiology and genetic basis can improve care provided for women affected by this diverse group of conditions. It is critical to assemble a multidisciplinary team of providers to optimize care for patients with inherited metabolic disorders.

A rare presentation of alkaptonuria: Extensive prostatic calculi with highlight of stones found in a unique paraprostatic urethral diverticulum

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AKU has a very low prevalence. This case sums of the two rarest entities of alkaptonuria and stones in a paraprostatic diverticulum also this case highlights the role endoscopic management of prostatolithiasis in alkaptonuria patient and the role of MRI in diagnosis of para prostatic diverticulum.

Introduction

We present a case of Alkaptonuria (AKU) presented with severe lower urinary tract symptoms (LUTS) secondary to extensive prostatic calculi deposited in the para prostatic diverticulum. Prostatic calculi are seen in chronic prostatitis, chronic pelvic pain syndrome and benign prostate hyperplasia; however, in patients with AKU, prostatic calculi and/or calcifications are more extensive. A para prostatic diverticulum is a rare entity in males; however, it should be considered in patients with AKU based on this case report.

Diagnosis, therapeutic interventions, and outcomes

A patient with AKU presented with extensive prostatic calculi that were deposited in para prostatic diverticulum, urethra and urinary bladder. The stones were successfully managed endoscopically.

Discussion

Paraprostatic diverticula or urethral diverticula are rare entities. They may be congenital or acquired due to recurrent Urinary Tract Infections (UTIs) or distal urethral obstruction. The distal obstruction of the urethra secondary to stones was the most likely etiology of the paraprostatic diverticulum in our case. The possible mechanisms behind stone formation in our case were chronic stasis and urinary infection within a urethral diverticulum proximal to the urethral obstruction.

Conclusion

This case sums a rare case of AKU and paraprostatic diverticular stones; in addition, it highlights the role endoscopic management of prostatolithiasis in AKU patient.

Remaining Challenges in the Treatment of Tyrosinemia from the Clinician's Viewpoint

This chapter provides a clinical perspective on the challenges that stand between current clinical practice and a cure for hepatorenal tyrosinemia (HT1). HT1 has been transformed in the last 50 years from an aggressive often undiagnosed childhood disease causing liver failure or liver cancer, with infant death in most patients, to a condition that is detectable at birth, and for which treatment with nitisinone (NTBC) and diet can prevent detectable liver or kidney abnormalities. What challenges remain? The properties of the affected metabolic pathway and the broad spectrum of severity seen in untreated patients are incompletely understood but potentially important for patients. Available treatments have potential complications, including liver transplantation (risks of surgery and of immunosuppression to prevent rejection), nitisinone and diet therapy (hypertyrosinemia, corneal opacities, nutritional imbalances and possibly developmental delay). The detection of liver cancer is imperfect and laborious. The effects of tyrosinemia during pregnancy are little-known. Although animal models of HT1 are becoming standard research tools in cell replacement and gene modification therapy, these techniques are not currently applicable to HT1 itself. Treatment adherence is variable, causing concern about long term outcome for some patients. Around the world, there are great disparities in the diagnosis and treatment of HT1. Most affected individuals are born in places where newborn screening for HT1 is not performed and where appropriate treatment is not available. We hope that this list will help to focus on some of these remaining obstacles to a cure for HT1.

Untargeted metabolomic analysis for the clinical screening of inborn errors of metabolism

Global metabolic profiling currently achievable by untargeted mass spectrometry-based metabolomic platforms has great potential to advance our understanding of human disease states, including potential utility in the detection of novel and known inborn errors of metabolism (IEMs). There are few studies of the technical reproducibility, data analysis methods, and overall diagnostic capabilities when this technology is applied to clinical specimens for the diagnosis of IEMs. We explored the clinical utility of a metabolomic workflow capable of routinely generating semi-quantitative z-score values for ~900 unique compounds, including ~500 named human analytes, in a single analysis of human plasma. We tested the technical reproducibility of this platform and applied it to the retrospective diagnosis of 190 individual plasma samples, 120 of which were collected from patients with a confirmed IEM. Our results demonstrate high intra-assay precision and linear detection for the majority compounds tested. Individual metabolomic profiles provided excellent sensitivity and specificity for the detection of a wide range of metabolic disorders and identified novel biomarkers for some diseases. With this platform, it is possible to use one test to screen for dozens of IEMs that might otherwise require ordering multiple unique biochemical tests. However, this test may yield false negative results for certain disorders that would be detected by a more well-established quantitative test and in its current state should be considered a supplementary test. Our findings describe a novel approach to metabolomic analysis of clinical specimens and demonstrate the clinical utility of this technology for prospective screening of IEMs.

Progress toward improved therapies for inborn errors of metabolism

Because of their prevalence, severity and lack of effective treatments, inborn errors of metabolism need novel and more effective therapeutic approaches. The opportunity for an early treatment coming from expanded newborn screening has made this need even more urgent. To meet this demand, a growing number of novel treatments are entering in the phase of clinical development. Strategies to overcome the detrimental consequences of the enzyme deficiencies responsible for inborn errors of metabolism have been focused on multiple fronts at the levels of the gene, RNA, protein and whole cell. These strategies have been accomplished using a wide spectrum of approaches ranging from small molecules to enzyme replacement therapy, cell and gene therapy. The applications of new technologies in the field of inborn errors of metabolism, such as genome editing, RNA interference and cell reprogramming, along with progress in pre-existing strategies, such as gene therapy or cell transplantation, have tremendous potential for clinical translation.

Alkaptonuria, more than just a mere disease

Alkaptonuria (AKU) is considered a rare autosomal recessive condition that results in an accumulation of homogentisic acid in body tissues and causes long-term clinical, neurological and psychological complications. We present a comprehensive evaluation of an atypical 46-year-old Caucasian male who developed all clinical diagnostic symptoms of AKU (ochronotic pigmentations, dark urine and clinical arthritis of major joints including spine) by 25 years of age, well before the typical age mentioned in many reviews. First signs of ochronotic ear pigmentations unexpectedly started appearing as early as 12 years of age. A long “disease-free” period typical in classical AKU patient was also absent. This case report highlights the importance of considering psychological issues in AKU patients. The patient showed symptoms of dysthymia reporting social isolation, diminished interest in pleasurable activities, feeling of worthlessness and irritability as major psychological issues. Early ochronotic pigmentation, advanced spinal myelopathy and arthropathy of major joints suggests aggressive course of the disease. Our patient underwent bilateral shoulder replacement due to AKU-induced arthropathy resulting in restoration of some range of motions. AKU is not fully understood and we recommend treating it as a multidimensional disease with simultaneous physiological, neurological and psychological effects. Early diagnosis, understanding of disease prognosis and emphasis on psychological health is needed to improve the quality of life of AKU patients.

Two novel mutations in the homogentisate-1,2-dioxygenase gene identified in Chinese Han Child with Alkaptonuria

Alkaptonuria (AKU) is an autosomal recessive disorder of tyrosine metabolism, which is caused by a defect in the enzyme homogentisate 1,2-dioxygenase (HGD) with subsequent accumulation of homogentisic acid. Presently, more than 100 HGD mutations have been identified as the cause of the inborn error of metabolism across different populations worldwide. However, the HGD mutation is very rarely reported in Asia, especially China. In this study, we present mutational analyses of HGD gene in one Chinese Han child with AKU, which had been identified by gas chromatography-mass spectrometry detection of organic acids in urine samples. PCR and DNA sequencing of the entire coding region as well as exon-intron boundaries of HGD have been performed. Two novel mutations were identified in the HGD gene in this AKU case, a frameshift mutation of c.115delG in exon 3 and the splicing mutation of IVS5+3 A>C, a donor splice site of the exon 5 and exon-intron junction. The identification of these mutations in this study further expands the spectrum of known HGD gene mutations and contributes to prenatal molecular diagnosis of AKU.

Genetics of the human metabolome, what is next?

Increases in throughput and decreases in costs have facilitated large scale metabolomics studies, the simultaneous measurement of large numbers of biochemical components in biological samples. Initial large scale studies focused on biomarker discovery for disease or disease progression and helped to understand biochemical pathways underlying disease. The first population-based studies that combined metabolomics and genome wide association studies (mGWAS) have increased our understanding of the (genetic) regulation of biochemical conversions. Measurements of metabolites as intermediate phenotypes are a potentially very powerful approach to uncover how genetic variation affects disease susceptibility and progression. However, we still face many hurdles in the interpretation of mGWAS data. Due to the composite nature of many metabolites, single enzymes may affect the levels of multiple metabolites and, conversely, levels of single metabolites may be affected by multiple enzymes. Here, we will provide a global review of the current status of mGWAS. We will specifically discuss the application of prior biological knowledge present in databases to the interpretation of mGWAS results and discuss the potential of mathematical models. As the technology continuously improves to detect metabolites and to measure genetic variation, it is clear that comprehensive systems biology based approaches are required to further our insight in the association between genes, metabolites and disease. This article is part of a Special Issue entitled: From Genome to Function.

Alkaptonuria

Alkaptonuria (AKU) is a rare disorder of autosomal recessive inheritance. It is caused by a mutation in a gene that results in the accumulation of homogentisic acid (HGA). Characteristically, the excess HGA means sufferers pass dark urine, which upon standing turns black. This is a feature present from birth. Over time patients develop other manifestations of AKU, due to deposition of HGA in collagenous tissues, namely ochronosis and ochronotic osteoarthropathy.   Although this condition does not reduce life expectancy, it significantly affects quality of life. The natural history of this condition is becoming better understood, despite gaps in knowledge. Clinical assessment of the condition has also improved along with the development of a potentially disease-modifying therapy. Furthermore, recent developments in AKU research have led to new understanding of the disease, and further study of the AKU arthropathy has the potential to influence therapy in the management of osteoarthritis.

Ochronotic osteoarthropathy in a mouse model of alkaptonuria, and its inhibition by nitisinone

BACKGROUND

Alkaptonuria (AKU) is a rare metabolic disease caused by deficiency of homogentisate 1,2 dioxygenase, an enzyme involved in tyrosine catabolism, resulting in increased circulating homogentisic acid (HGA). Over time HGA is progressively deposited as a polymer (termed ochronotic pigment) in collagenous tissues, especially the cartilages of weight bearing joints, leading to severe joint disease.

OBJECTIVES

To characterise blood biochemistry and arthropathy in the AKU mouse model (Hgd-/-). To examine the therapeutic effect of long-term treatment with nitisinone, a potent inhibitor of the enzyme that produces HGA.

METHODS

Lifetime levels of plasma HGA from AKU mice were measured by high-performance liquid chromatography (HPLC). Histological sections of the knee joint were examined for pigmentation. The effect of nitisinone treatment in both tissues was examined.

RESULTS

Mean (±SE) plasma HGA levels were 3- to 4-fold higher (0.148±0.019 mM) than those recorded in human AKU. Chondrocyte pigmentation within the articular cartilage was first observed at 15 weeks, and found to increase steadily with mouse age. Nitisinone treatment reduced plasma HGA in AKU mice throughout their lifetime, and completely prevented pigment deposition.

CONCLUSIONS

The AKU mouse was established as a model of both the plasma biochemistry of AKU and its associated arthropathy. Early-stage treatment of AKU patients with nitisinone could prevent the development of associated joint arthropathies. The cellular pathology of ochronosis in AKU mice is identical to that observed in early human ochronosis and thus is a model in which the early stages of joint pathology can be studied and novel interventions evaluated.

Lower urinary tract symptoms and prostatic calculi: A rare presentation of alkaptonuria

Alkaptonuria is a rare tyrosine metabolic disorder. A deficiency of homogentisic acid oxidase leads to accumulation of homogentisic acid in the body. Dark-colored urine, cutaneous pigmentations and musculoskeletal deformities are characteristic features. Storage and voiding lower urinary tract symptoms due to prostatic calculi is a rare presentation.

Shoulder arthroplasty in alkaptonuric arthropathy: a clinical case report and literature review

Alkaptonuria is a rare hereditary metabolic disease of autosomal recessive inheritance, resulting from deficiency of the enzyme homogentisic acid oxidase. The term "alkaptonuria" was first used in 1859 by Boedeker to describe a patient's urinary reducing compound, and in 1866, Virchow coined the term "ochronosis" due to typical yellow pigmentation. Deposition of this pigment in articular cartilage leads to ochronotic arthropathy, the most incapacitating complication of alkaptonuria. We report a rare case of shoulder ochronotic arthritis, treated with total shoulder arthroplasty, achieving a successful long-term clinical and radiological outcomes.

The role of calcified cartilage and subchondral bone in the initiation and progression of ochronotic arthropathy in alkaptonuria

OBJECTIVE

Alkaptonuria is a genetic disorder of tyrosine metabolism, resulting in elevated circulating concentrations of homogentisic acid. Homogentisic acid is deposited as a polymer, termed ochronotic pigment, in collagenous tissues, especially cartilages of weight-bearing joints, leading to a severe osteoarthropathy. We undertook this study to investigate the initiation and progression of ochronosis from the earliest detection of pigment through complete joint failure.

METHODS

Nine joint samples with varying severities of ochronosis were obtained from alkaptonuria patients undergoing surgery and compared to joint samples obtained from osteoarthritis (OA) patients. Samples were analyzed by light and fluorescence microscopy, 3-dimensional scanning electron microscopy (SEM), and the quantitative backscattered electron mode of SEM. Cartilage samples were mechanically tested by compression to determine Young's modulus of pigmented, nonpigmented, and OA cartilage samples.

RESULTS

In alkaptonuria samples with the least advanced ochronosis, pigment was observed intracellularly and in the territorial matrix of individual chondrocytes at the boundary of the subchondral bone and calcified cartilage. In more advanced ochronosis, pigmentation was widespread throughout the hyaline cartilage in either granular composition or as blanket pigmentation in which there is complete and homogenous pigmentation of cartilage matrix. Once hyaline cartilage was extensively pigmented, there was aggressive osteoclastic resorption of the subchondral plate. Pigmented cartilage became impacted on less highly mineralized trabeculae and embedded in the marrow space. Pigmented cartilage samples were much stiffer than nonpigmented or OA cartilage as revealed by a significant difference in Young's modulus.

CONCLUSION

Using alkaptonuria cartilage specimens with a wide spectrum of pigmentation, we have characterized the progression of ochronosis. Intact cartilage appears to be resistant to pigmentation but becomes susceptible following focal changes in calcified cartilage. Ochronosis spreads throughout the cartilage, altering the mechanical properties. In advanced ochronosis, there is aggressive resorption of the underlying calcified cartilage leading to an extraordinary phenotype in which there is complete loss of the subchondral plate. These findings should contribute to better understanding of cartilage-subchondral interactions in arthropathies.

Garrod's fourth inborn error of metabolism solved by the identification of mutations causing pentosuria

Pentosuria is one of four conditions hypothesized by Archibald Garrod in 1908 to be inborn errors of metabolism. Mutations responsible for the other three conditions (albinism, alkaptonuria, and cystinuria) have been identified, but the mutations responsible for pentosuria remained unknown. Pentosuria, which affects almost exclusively individuals of Ashkenazi Jewish ancestry, is characterized by high levels of the pentose sugar L-xylulose in blood and urine and deficiency of the enzyme L-xylulose reductase. The condition is autosomal-recessive and completely clinically benign, but in the early and mid-20th century attracted attention because it was often confused with diabetes mellitus and inappropriately treated with insulin. Persons with pentosuria were identified from records of Margaret Lasker, who studied the condition in the 1930s to 1960s. In the DCXR gene encoding L-xylulose reductase, we identified two mutations, DCXR c.583ΔC and DCXR c.52(+1)G > A, each predicted to lead to loss of enzyme activity. Of nine unrelated living pentosuric subjects, six were homozygous for DCXR c.583ΔC, one was homozygous for DCXR c.52(+1)G > A, and two were compound heterozygous for the two mutant alleles. L-xylulose reductase was not detectable in protein lysates from subjects' cells and high levels of xylulose were detected in their sera, confirming the relationship between the DCXR genotypes and the pentosuric phenotype. The combined frequency of the two mutant DCXR alleles in 1,067 Ashkenazi Jewish controls was 0.0173, suggesting a pentosuria frequency of approximately one in 3,300 in this population. Haplotype analysis indicated that the DCXR c.52(+1)G > A mutation arose more recently than the DCXR c.583ΔC mutation.

Succinic semialdehyde dehydrogenase: biochemical-molecular-clinical disease mechanisms, redox regulation, and functional significance

Succinic semialdehyde dehydrogenase (SSADH; aldehyde dehydrogenase 5a1, ALDH5A1; E.C. 1.2.1.24; OMIM 610045, 271980) deficiency is a rare heritable disorder that disrupts the metabolism of the inhibitory neurotransmitter 4-aminobutyric acid (GABA). Identified in conjunction with increased urinary excretion of the GABA analog gamma-hydroxybutyric acid (GHB), numerous patients have been identified worldwide and the autosomal-recessive disorder has been modeled in mice. The phenotype is one of nonprogressive neurological dysfunction in which seizures may be prominently displayed. The murine model is a reasonable phenocopy of the human disorder, yet the severity of the seizure disorder in the mouse exceeds that observed in SSADH-deficient patients. Abnormalities in GABAergic and GHBergic neurotransmission, documented in patients and mice, form a component of disease pathophysiology, although numerous other disturbances (metabolite accumulations, myelin abnormalities, oxidant stress, neurosteroid depletion, altered bioenergetics, etc.) are also likely to be involved in developing the disease phenotype. Most recently, the demonstration of a redox control system in the SSADH protein active site has provided new insights into the regulation of SSADH by the cellular oxidation/reduction potential. The current review summarizes some 30 years of research on this protein and disease, addressing pathological mechanisms in human and mouse at the protein, metabolic, molecular, and whole-animal level.

Novel mutations in the homogentisate 1,2 dioxygenase gene identified in Jordanian patients with alkaptonuria

This study was conducted to identify mutations in the homogentisate 1,2 dioxygenase gene (HGD) in alkaptonuria patients among Jordanian population. Blood samples were collected from four alkaptonuria patients, four carriers, and two healthy volunteers. DNA was isolated from peripheral blood. All 14 exons of the HGD gene were amplified using the polymerase chain reaction (PCR) technique. The PCR products were then purified and analyzed by sequencing. Five mutations were identified in our samples. Four of them were novel C1273A, T1046G, 551-552insG, T533G and had not been previously reported, and one mutation T847C has been described before. The types of mutations identified were two missense mutations, one splice site mutation, one frameshift mutation, and one polymorphism. We present the first molecular study of the HGD gene in Jordanian alkaptonuria patients. This study provides valuable information about the molecular basis of alkaptonuria in Jordanian population.

Nine cases of Alkaptonuria in one family in southern Jordan

Alkaptonuria is a rare autosomal recessive metabolic disorder characterized by a deficiency of homogentisate 1,2-dioxygenase (HGO) in the liver. This results in excretion of large quantities of homogentisic acid (HGA) (also called alkapton) in the urine and a slowly progressive deposition of homogentisic acid and its oxidative product in connective tissues. Clinical characteristic features of alkaptonuria are darkening of urine, bluish-dark pigmentation of connective tissues (ochronosis) and arthritis of large joints and spine. Cardiovascular and genitourinary systems may also be affected. In this report, we present the initial results of screening family members with history of alkaptonuria in southern region of Jordan. We present 9 cases of alkaptonuria (two males and seven females) in one Jordanian family. The history, signs and symptoms, diagnostic techniques and treatment options of alkaptonuria are reviewed in this article.

Application of liquid chromatography-tandem mass spectrometry (LC-MS/MS) in screening of high risk children with inherited metabolic diseases in northern China

OBJECTIVE

To investigate the morbidity and distribution of 35 inherited metabolic diseases in high risk children by LC-MS/MS in northern China.

METHODS

The dry blood on filter papers, collected from 2760 children clinically suspected to have inherited metabolic diseases from more than sixty hospitals in north China, was tested by LC-MS/MS. The specimen was extracted out of the dry blood on filter paper, derivatized before being injected into LCMS/MS. The LC-MS/MS methodology used in the study was transferred from Pediatrix Medical Group (1301 Concord Terrace, Sunrise, FL 33323), validated in our lab and further compared with United States CDC standard. The positive results were further confirmed by gas chromatography-mass, other laboratory tests and clinical symptoms.

RESULTS

249 of the 2760 children (9%) were diagnosed with one or more of twenty-one disorders. Out of 249 patients, there are 41 (16.5%) fatty acid disorders, 71 (28.5%) amino acid diseases, and 137 (55%) organic acidemias. 48 of the 249 patients (19.3%) were neonates, including 11 (22.9%) with fatty acid disorders, 15 (31.3%) with amino acid diseases, and 22 (45.8%) with organic acidemias. 201 of the 249 patients were elder than 28 days, and was composed of 30 (14.9%) with fatty acid disorders, 56 (27.9%) with amino acid diseases, 115 (57.2%) with organic acidemias.

CONCLUSIONS

The LC-MS/MS technology can be used to detect over 30 inherited metabolic disorders for Chinese pediatric clinic in a single collection of blood. The morbidity of IMD (9%) is relatively high among high risk children, thus we highly suggest that we shall provide initial screening of over 30 IMDs for the high risk children in China using the technology of LC-MS/MS.