Radiological evolution of spinal disease in alkaptonuria and the effect of nitisinone

Objectives

Ochronotic spondyloarthropathy represents one of the main clinical manifestations of alkaptonuria (AKU); however, prospective data and description of the effect of nitisinone treatment are lacking.

Methods

Patients with AKU aged 25 years or older were randomly assigned to receive either oral nitisinone 10 mg/day (N=69) or no treatment (N=69). Spine radiographs were recorded yearly at baseline, 12, 24, 36 and 48 months, and the images were scored for the presence of intervertebral space narrowing, soft tissue calcifications, vacuum phenomena, osteophytes/hyperostosis and spinal fusion in the cervical, thoracic and lumbosacral segment at each of the time points.

Results

At baseline, narrowing of the intervertebral spaces, the presence of osteophytes/hyperostosis and calcifications were the three most frequent radiographic features in AKU. The rate of progression of the five main features during the 4 years, ranked from the highest to lowest was as follows: intervertebral spaces narrowing, calcifications, vacuum phenomena, osteophytes/hyperostosis and fusions. The rate of progression did not differ between the treated and untreated groups in any of the five radiographic parameters except for a slower rate of progression (sum of all five features) in the treatment group compared with the control group (0.45 (1.11) nitisinone vs 0.74 (1.11) controls, p=0.049) in the thoracic segment.

Conclusion

The present study shows a relatively slow but significant worsening of radiographic features in patients with AKU over 4 years. Our results demonstrate a modest beneficial effect of 10 mg/day of nitisinone on the slowly progressing spondylosis in AKU during the relatively limited follow-up time.

Trial registration number

NCT01916382.

A novel mutation in the homogentisate 1,2 dioxygenase gene identified in Chinese Hani pediatric patients with Alkaptonuria

BACKGROUND

Alkaptonuria (AKU) is a rare tyrosine metabolism disorder caused by homogentisate 1,2-dioxygenase (HGD) mutations and homogentisic acid (HGA) accumulation. In this study, we investigated the genotype-phenotype relationship in AKU patients with a novel HGD gene mutation from a Chinese Hani family.

METHODS

Routine clinical examination and laboratory evaluation were performed, urine alkalinization test and urinary gas chromatography-mass spectrometry were used to assess HGA. Gene sequencing was utilized to study the defining features of AKU. NetGene2-2.42 and BDGP software was used to predict protein structure online. Flow cytometry and RT-PCR were used to analyze HGD proteins and HGD mRNA, respectively.

RESULTS

Two pediatric patients fulfilled diagnostic criteria for AKU with eddish-brown or black diapers and urine HGA testing. Sequencing testing revealed that all members of this family had a novel samesense mutation c.15G>A at the edge of exon 1 of the HGD. By flow cytometry, the expression of HGD protein in the pediatric patients' peripheral blood mononuclear cells was barely expressed. NetGene2-2.42 and BDGP software showed that the mutation reduced the score of the 5' splice donor site and disrupted its normal splicing, and the RT-PCR product also demonstrated that the defect in the HGD protein was due to the lack of the first exon containing the start codon ATG after the mutation.

CONCLUSIONS

The novel mutation c.15G > A in HGD is associated with the AKU phenotype. It may affect the splicing of exon 1, leading to exon skipping, which impairs the structure and function of the protein.

Variant Analysis of Alkaptonuria Families with Significant Founder Effect in Jordan

Background

Metabolic disorder alkaptonuria is an autosomal recessive disorder caused by mutations in the HGD gene, and a deficiency HGD enzyme activity results in an accumulation of homogentisic acid (HGA), ochronosis, and destruction of connective tissue.

Methods

We clinically evaluated 18 alkaptonuria patients (age range, 3 to 60 years) from four unrelated families. Furthermore, 11 out of 18 alkaptonuria patients and 7 unaffected members were enrolled for molecular investigations by utilizing Sanger sequencing to identify variants of the 14 exons of HGD gene.

Results

We found that the seven patients from the 4 unrelated families carried a recurrent pathogenic missense variant (c.365C>T, p. Ala122Val) in exon 6 of HGD gene. The variant was fully segregated with the disease in affected family members while the other unaffected family members were heterozygous carriers for this variant. Additionally, the clinical features were fully predicted with alkaptonuria disorder.

Conclusion

In this study, we confirmed that the most common variants in Jordanian AKU patients was c.365C>T, p. Ala122Val in exon 6 of HGD gene. Additionally, we correlated the clinical and genetic features of AKU patients at various ages (3-60 years).

Founder effects of the homogentisate 1,2-dioxygenase (HGD) gene in a gypsy population and mutation spectrum in the gene among alkaptonuria patients from India

INTRODUCTION

Alkaptonuria (AKU) is a rare metabolic disease. The global incidence is 1:100,000 to 1:250,000. However, identification of a founder mutation in a gypsy population from India prompted us to study the prevalence of AKU in this population and to do molecular typing in referred cases of AKU from the rest of India.

OBJECTIVE

To determine the prevalence of AKU in the gypsy population predominantly residing in the seven districts of Tamil Nadu. To determine the molecular characteristic of AKU cases referred to our clinic from various parts of India.

METHOD

Urine spot test to detect homogentisic acid followed by quantitative estimation using high-performance liquid chromatography in 499 participants from the gypsy population and confirming the founder mutation in those with high levels by sequencing. Sequence the homogentisate 1,2-dioxygenase (HGD) gene to identify mutations and variants in 29 AKU non-gypsy cases.

RESULTS

The founder mutation was detected in homozygous state in 41/499 AKU-affected individuals of the gypsy community giving a high prevalence of 8.4%. Low back pain, knee pain, and eye and ear pigmentation were the most common symptoms and signs respectively. The commonest mutation identified in the non-gypsy AKU cases was p.Ala122Val.

CONCLUSION

High prevalence of AKU in the inbred gypsy population at 8.4% was detected confirming the founder effect. Urine screening provided a cost-effective method to detect the disease early. Mutation spectrum is varied in the rest of the Indian population. This study identified maximum number of mutations in exon 6 of the HGD gene. Key Points • High prevalence (8.4%) of alkaptonuria (AKU) in the gypsy population due to founder mutation in the HGD gene. • Inbreeding exemplifies the founder effects of this rare genetic disorder. • Urinary screening is a cost-effective method in this community for early detection of AKU and intervention. • The mutation spectrum causing AKU is diverse in the rest of the Indian population.

ARTHROPLASTY IN ALKAPTONURIC OCHRONOSIS

Ochronotic degenerative arthropathy occurs in patients with alkaptonuria. Alkaptonuria disorder is an extremely rare disease characterized by black pigmentation of various tissues (e.g., cartilage and connective tissue). Ochronotic arthropathy is a disabling disease that primarily affects the large joints. Like other metabolic diseases that involve the musculoskeletal system, care must be taken with regard to the quality of the affected bones, tendons and ligaments, and therefore the stability and survival of joint prosthesis. The following is a report of a 66-year-old man affected by several musculoskeletal manifestations of alkaptonuria with severe joints disruption, who was successfully treated with total left hip and total right knee replacements. Surgical, anesthesiological and postoperative management of these patients may require more vigilance due to the associated comorbidities of this disorder.

An Unusual Cause of Myelopathy: Ochronotic Spondyloarthropathy With Positive HLA B27

Ochronosis is a late developing complication of alkaptonuria, a black brownish pigment in the fibrous and cartilaginous tissues. Although most previous studies reported alkaptonuria and back pain due to ochronosis, thoracic myelopathy is an extremely rare complication. In this report, a paraparetic patient who has ochronotic spondiloarthropathy with the presence of HLA B27 antigen is described. He had low back and leg pain and morning stiffness for 5 yrs. Last year, these were followed by tingling, numbness, and weakness the in lower extremities and he was operated on with preliminary diagnosis of prolapsed disc herniation and cord compression. Surgery is suggested for disc herniations related to ochronotic spondyloarthropathy if it is necessary or neurologic symptoms are present. However, his pain and weakness have partially recovered after the operation. After medical and physical treatment, he showed clinically significant improvements. This case report demonstrates that the management of ochronosis needs a multidisciplinary approach with physiologic, neurologic, and psychologic effects and proper treatment may significantly improve functional outcomes in these patients.

Long-term result of arthroplasty in the treatment of a case of ochronotic arthropathy

Alkaptonuria is a rare metabolic disease caused by a partial or total deficiency of homogentisic acid oxidase, which results in excess homogentisic acid (HGA) levels. Homogentisic acid and its oxidation products can accumulate in hyaline cartilage, tendons, and ligaments. A 55-year-old male was admitted complaining of worsening chronic pain in his left knee. A radiographic evaluation showed tricompartmental end- stage osteoarthritis. A cemented total knee replacement was performed. At the 10-year follow-up, he had returned to full activity, had no knee pain, and was very satisfied with the outcome. No abnormality was observed in the femoral, tibial, or patellar components on radiography. We believe that total knee replacement is a good option in a patient with marked degenerative arthritis secondary to ochronotic arthritis.

Genetics of alkaptonuria – an overview

Alkaptonuria (AKU) is the first described inborn error of metabolism and a classical example of rare autosomal recessive disease. AKU patients carry homozygous or compound heterozygous mutations of the gene coding for enzyme homogentisate dioxygenase (HGD) involved in metabolism of tyrosine. The metabolic block in AKU causes accumulation of homogentisic acid (HGA) that, with advancing age of the patient, leads to severe and painful ochronotic arthropathy. HGD gene was mapped to chromosome 3q13.3 and is composed of 14 exons. In about 400 patients, 142 pathogenic variants were reported that are listed in HGD mutations database (http://hgddatabase.cvtisr.sk/). In this review, we summarise different aspects of AKU genetics and impact of the HGD variants on enzyme function.

Twelve novel HGD gene variants identified in 99 alkaptonuria patients: focus on 'black bone disease' in Italy

Alkaptonuria (AKU) is an autosomal recessive disorder caused by mutations in homogentisate-1,2-dioxygenase (HGD) gene leading to the deficiency of HGD enzyme activity. The DevelopAKUre project is underway to test nitisinone as a specific treatment to counteract this derangement of the phenylalanine-tyrosine catabolic pathway. We analysed DNA of 40 AKU patients enrolled for SONIA1, the first study in DevelopAKUre, and of 59 other AKU patients sent to our laboratory for molecular diagnostics. We identified 12 novel DNA variants: one was identified in patients from Brazil (c.557T>A), Slovakia (c.500C>T) and France (c.440T>C), three in patients from India (c.469+6T>C, c.650-85A>G, c.158G>A), and six in patients from Italy (c.742A>G, c.614G>A, c.1057A>C, c.752G>A, c.119A>C, c.926G>T). Thus, the total number of potential AKU-causing variants found in 380 patients reported in the HGD mutation database is now 129. Using mCSM and DUET, computational approaches based on the protein 3D structure, the novel missense variants are predicted to affect the activity of the enzyme by three mechanisms: decrease of stability of individual protomers, disruption of protomer-protomer interactions or modification of residues in the region of the active site. We also present an overview of AKU in Italy, where so far about 60 AKU cases are known and DNA analysis has been reported for 34 of them. In this rather small group, 26 different HGD variants affecting function were described, indicating rather high heterogeneity. Twelve of these variants seem to be specific for Italy.

Redox proteomics gives insights into the role of oxidative stress in alkaptonuria

Alkaptonuria (AKU) is an ultra-rare metabolic disorder of the catabolic pathway of tyrosine and phenylalanine that has been poorly characterized at molecular level. As a genetic disease, AKU is present at birth, but its most severe manifestations are delayed due to the deposition of a dark-brown pigment (ochronosis) in connective tissues. The reasons for such a delayed manifestation have not been clarified yet, though several lines of evidence suggest that the metabolite accumulated in AKU sufferers (homogentisic acid) is prone to auto-oxidation and induction of oxidative stress. The clarification of the pathophysiological molecular mechanisms of AKU would allow a better understanding of the disease, help find a cure for AKU and provide a model for more common rheumatic diseases. With this aim, we have shown how proteomics and redox proteomics might successfully overcome the difficulties of studying a rare disease such as AKU and the limitations of the hitherto adopted approaches.

On the ocular findings in ochronosis: a systematic review of literature

BACKGROUND

Ochronosis/Alkaptonuria is a tyrosine metabolism disorder where accumulation of homogentisic acid, in eye, skin, cartilage and several other connective tissues leads to a black pigmentation of the affected tissues. It is autosomal-recessive inherited in men with a frequency of 1-9/1,000,000. While it is clear that pigment deposits lead to joint destruction, renal stone formation and cardiac valvulopathy respectively, the significance of ocular findings is still unclear. We therefore aim to evaluate the frequency and clinical significance of ocular findings in ochronosis and discuss possible therapeutic options.

METHODS

Systematic review of literature via Medline and Web of Science. Only case reports in English, German, French, Spanish or Italian documenting detailed ophthalmologic examination were included.

RESULTS

Our search revealed 36 case reports including 40 patients. Average age at the onset of ocular signs was 40.6 years. The most frequent sign was symmetric brown sclera pigmentation present in 82.5 percent of the patients. "Oil-drops", brown pigment spots in the limbus are generally considered pathognomonic but were a little less frequent (75 percent). Vermiform pigment deposits at the level of the conjunctiva or increased conjunctival vessel diameter is also frequent. We found an increased incidence of central vein occlusion and elevated intraocular pressure going along with chamber angle hyperpigmentation. Another condition observed twice is rapid progressive astigmatism attributable to corneoscleral pigment accumulation.

CONCLUSION

Our observations suggest that ocular findings are of double relevance. First, characteristic ocular findings can anticipate the time of diagnosis and second, ocular findings may complicate to various conditions putting sight at risk. Opthalmologists and general physicians should be aware of both. Therapeutic options include protein restriction, administration of high dose vitamin C or nitisonone. Evidence for all of them is limited.

Total hip replacement for an ochronotic patient: A technical trick

Patient: Male, 46

Final Diagnosis: Akkaptonuria

Symptoms: Hip pain

Medication: —

Clinical Procedure: Total hip replacement

Specialty: Orthopedics and Traumatology

Identification of 11 Novel Homogentisate 1,2 Dioxygenase Variants in Alkaptonuria Patients and Establishment of a Novel LOVD-Based HGD Mutation Database

Enzymatic loss in alkaptonuria (AKU), an autosomal recessive disorder, is caused by mutations in the homogentisate 1,2 dioxygenase (HGD) gene, which decrease or completely inactivate the function of the HGD protein to metabolize homogentisic acid (HGA). AKU shows a very low prevalence (1:100,000-250,000) in most ethnic groups, but there are countries with much higher incidence, such as Slovakia and the Dominican Republic. In this work, we report 11 novel HGD mutations identified during analysis of 36 AKU patients and 41 family members from 27 families originating from 9 different countries, mainly from Slovakia and France. In Slovak patients, we identified two additional mutations, thus a total number of HGD mutations identified in this small country is 12. In order to record AKU-causing mutations and variants of the HGD gene, we have created a HGD mutation database that is open for future submissions and is available online ( http://hgddatabase.cvtisr.sk/ ). It is founded on the Leiden Open (source) Variation Database (LOVD) system and includes data from the original AKU database ( http://www.alkaptonuria.cib.csic.es ) and also all so far reported variants and AKU patients. Where available, HGD-haplotypes associated with the mutations are also presented. Currently, this database contains 148 unique variants, of which 115 are reported pathogenic mutations. It provides a valuable tool for information exchange in AKU research and care fields and certainly presents a useful data source for genotype-phenotype correlations and also for future clinical trials.

Endogenous ochronosis: case report and a systematic review of the literature

BACKGROUND

Endogenous ochronosis (EO) is a rare autosomal recessive disorder due to accumulation of oxidized and polymerized forms of homogentisic acid (HGA) in connective tissues, giving them a deep dark blue pigmentation.

AIM

Through a new Tunisian case of EO and a review of the literature, we aimed to define the epidemioclinical features of EO, its diagnostic criteria, and evolution.

METHODS

Three hundred and forty patients were enrolled through 54 articles and four abstracts.

CASE REPORT

A 35-year-old woman, born in consanguineous parents, presented with blue-grey patches of fingernails, first interdigital spaces, and ears with brown conjunctival pigmentation. Urine specimen turned dark on standing overnight. The diagnosis of EO was confirmed by urinary high levels of HGA. Investigations revealed radiologic signs of ochronotic arthropathy.

REVIEW OF THE LITERATURE

EO is ubiquitary. Its prevalence was estimated at almost 6.5 cases/year. The mean age at diagnosis was 55.9 years (M/F: 1.85). Onset symptoms mainly consisted in cutaneous signs. Ochronotic arthropathy was the most frequently reported manifestation. Treatment was mainly symptomatic.

DISCUSSION

EO is often revealed in adulthood mainly after the fourth decade. Urinary darkening is the first sign of the disease but is rarely reported as an onset sign. Skin signs are the alerting features. Ochronotic arthropathy is insidious but may be debilitating. No specific medical treatment of EO is available.

CONCLUSION

Cutaneous manifestations are the hallmarks of OE. As vital organ involvement has been reported, close monitoring and continuous surveillance is warranted.

Mutation spectrum of homogentisic acid oxidase (HGD) in alkaptonuria

Alkaptonuria (AKU) is a rare autosomal recessive metabolic disorder, characterized by accumulation of homogentisic acid, leading to darkened urine, pigmentation of connective tissue (ochronosis), joint and spine arthritis, and destruction of cardiac valves. AKU is due to mutations in the homogentisate dioxygenase gene (HGD) that converts homogentisic acid to maleylacetoacetic acid in the tyrosine catabolic pathway. Here we report a comprehensive mutation analysis of 93 patients enrolled in our study, as well as an extensive update of all previously published HGD mutations associated with AKU. Within our patient cohort, we identified 52 HGD variants, of which 22 were novel. This yields a total of 91 identified HGD variations associated with AKU to date, including 62 missense, 13 splice site, 10 frameshift, 5 nonsense, and 1 no-stop mutation. Most HGD variants reside in exons 3, 6, 8, and 13. We assessed the potential effect of all missense variations on protein function, using five bioinformatic tools specifically designed for interpretation of missense variants (SIFT, POLYPHEN, PANTHER, PMUT, and SNAP). We also analyzed the potential effect of splice-site variants using two different tools (BDGP and NetGene2). This study provides valuable resources for molecular analysis of alkaptonuria and expands our knowledge of the molecular basis of this disease.

Ochronosis as an unusual cause of valvular defect: a case report

Introduction

Alkaptonuria (also known as ochronosis) is a genetic disorder characterised by the accumulation of homogentisic acid deposits in connective tissue. In rare cases, ochronosis can cause valvular heart disease.

Case presentation

We present the case of a 68-year-old Caucasian man with alkaptonuria-associated degenerative valvular defects with aortic, mitral and tricuspid valve insufficiency. The patient did not have any cardiac complaints and was referred to our clinic for evaluation of a conspicuous new heart murmur.

Conclusion

This case report shows that early diagnosis of cardiovascular ochronosis gives us the opportunity to use conservative treatment to slow down the progression of valvular dysfunction.

A novel missense HGD gene mutation, K57N, in a patient with alkaptonuria

Alkaptonuria is a rare recessive disorder of phenylalanine/tyrosine metabolism due to a defect in the enzyme homogentisate 1,2-dioxygenase (HGD) caused by mutations in the HGD gene. We report the case of a 38 year-old male with known alkaptonuria who was referred to an adult metabolic clinic after initially presenting to an emergency department with renal colic and subsequently passing black ureteric calculi. He complained of severe debilitating lower back pain, worsening over the last few years. A CT scan revealed marked degenerative changes and severe narrowing of the disc spaces along the entire lumbar spine. Sequencing of the HGD gene revealed that he was a compound heterozygote for a previously described missense mutation in exon 13 (G360R) and a novel missense mutation in exon 3 (K57N). Lys(57) is conserved among species and mutation of this residue is predicted to affect HGD protein function by interfering with substrate traffic at the active site. In summary, we describe an alkaptonuric patient and report a novel missense HGD mutation, K57N.

R58fs mutation in the HGD gene in a family with alkaptonuria in the UAE

This study was conducted to determine the prevalence of alkaptonuria in the UAE population and to identify the genotype of affected individuals. In a 3 stage sampling technique 2981 pupils from Government schools in Al Ain and private schools in Dubai were selected to take part in the study, of whom 2857 provided urine samples. Urine collected was analysed for homogentisic acid by gas chromatography-mass spectrometry. Genomic DNA was isolated from the white blood cells of all family members of the affected case following standard established protocols. Specific PRC primers were designed to amplify all 14 exons of the HGD gene with the flanking intronic sequences including the splice site sequences. 2857 children returned a viable urine sample, of which one was highly positive for homogentisic acid. All 12 members of this girl's family were studied and one, a 22 year old brother, was found to excrete HGA. Another, a sister who had not provided a urine sample, was discovered by genetic testing. There were no complaints of joint pain or other symptoms in any member of this family. Parents were first cousins. We found a single nucleotide deletion c.342delA, located in exon 3, which resulted in a frameshift at amino acid position 58 (p.Arg58fs or p.R58fs). Alkaptonuria may be more common than it is thought to be with an allele prevalence estimated at 0.0107 (95% CI 0.000392-0.03473). The R58fs mutation is old, perhaps having occurred several thousand years ago, and has spread over a large geographical area.

Rapid detection methods for five HGO gene mutations causing alkaptonuria

Alkaptonuria (AKU) is an autosomal recessive disorder caused by the deficiency of homogentisate 1,2 dioxygenase (HGO) activity. The disease is characterized by homogentisic aciduria, ochronosis and ochronotic arthritis. AKU shows a very low prevalence (1:250 000), in most ethnic groups. Altogether 43 HGO mutations have been identified in approximately 100 patients. In Slovakia, however, the incidence of this disorder rises up to 1:19 000, and 10 different AKU mutations have been identified in this relatively small country. Here, we report detection methods developed for rapid identification of five HGO mutations. PCR primers were designed enabling detection of mutations IVS5 + 1G-->A, R58fs, and V300G by restriction digestion of amplification-created restriction sites (ACRS). Mutation G152fs is readily identified by heteroduplex analysis, and G161R by amplification refractory mutation system (ARMS) PCR.

Molecular analyses of the HGO gene mutations in Turkish alkaptonuria patients suggest that the R58fs mutation originated from central Asia and was spread throughout Europe and Anatolia by human migrations

Alkaptonuria (AKU) is a rare metabolic disorder of phenylalanine catabolism that is inherited as an autosomal recessive trait. AKU is caused by loss-of-function mutations in the homogentisate 1,2-dioxygenase (HGO) gene. The deficiency of homogentisate 1,2-dioxygenase activity causes homogentisic aciduria, ochronosis and arthritis. We present the first molecular study of the HGO gene in Turkish AKU patients. Seven unrelated AKU families from different regions in Turkey were analysed. Patients in three families were homozygous for the R58fs mutation; another three families were homozygous for the R225H mutation; and one family was homozygous for the G270R mutation. Analysis of nine intragenic HGO polymorphisms showed that the R58fs, R225H and G270R Turkish AKU mutations are associated with specific HGO haplotypes. The comparison with previously reported haplotypes associated with these mutations from other populations revealed that the R225H is a recurrent mutation in Turkey, whereas G270R most likely has a Slovak origin. Most interestingly, these analyses showed that the Turkish R58fs mutation shares an HGO haplotype with the R58fs mutation found in Finland, Slovakia and India, suggesting that R58fs is an old AKU mutation that probably originated in central Asia and spread throughout Europe and Anatolia during human migrations.

Natural history of alkaptonuria

BACKGROUND

Alkaptonuria, caused by mutations in the HGO gene and a deficiency of homogentisate 1,2-dioxygenase, results in an accumulation of homogentisic acid (HGA), ochronosis, and destruction of connective tissue. There is no effective therapy for this disorder, although nitisinone inhibits the enzyme that produces HGA. We performed a study to delineate the natural history of alkaptonuria.

METHODS

We evaluated 58 patients with alkaptonuria (age range, 4 to 80 years), using clinical, radiographic, biochemical, and molecular methods. A radiographic scoring system was devised to assess the severity of spinal and joint damage. Two patients were treated with nitisinone for 10 and 9 days, respectively.

RESULTS

Life-table analyses showed that joint replacement was performed at a mean age of 55 years and that renal stones developed at 64 years, cardiac-valve involvement at 54 years, and coronary-artery calcification at 59 years. Linear regression analysis indicated that the radiographic score for the severity of disease began increasing after the age of 30 years, with a more rapid increase in men than in women. Twenty-three new HGO mutations were identified. In a 51-year-old woman, urinary HGA excretion fell from 2.9 to 0.13 g per day after a 10-day course of nitisinone (7 days at a dose of 0.7 mg per day and 3 days at 2.8 mg per day). In a 59-year-old woman, urinary HGA fell from 6.4 g to 1.7 g per day after nine days of treatment with nitisinone (0.7 mg per day). Plasma tyrosine levels in these patients rose from approximately 1.1 mg per deciliter (60 micromol per liter) in both to approximately 12.8 mg per deciliter (700 micromol per liter) and 23.6 mg per deciliter (1300 micromol per liter), respectively, with no clinical signs or symptoms.

CONCLUSIONS

The reported data on the natural history of alkaptonuria provide a basis for the evaluation of long-term therapies. Although nitisinone can reduce HGA production in humans with homogentisate 1,2-dioxygenase deficiency, the long-term safety and efficacy of this treatment require further evaluation.

Exacerbation of the ochronosis of alkaptonuria due to renal insufficiency and improvement after renal transplantation

In alkaptonuria, homogentisate 1,2-dioxygenase deficiency causes tissue accumulation of homogentisic acid (HGA), followed by signs and symptoms of ochronosis. These include massive urinary excretion of HGA, arthritis and joint destruction, pigmentation of cartilage and connective tissue, and cardiac valve deterioration. We describe a 46-year-old man with alkaptonuria and diabetic renal failure whose plasma HGA concentration was twice that of any other alkaptonuria patient, and whose ochronosis progressed much more rapidly than that of his two alkaptonuric siblings. After renal transplantation, the plasma HGA normalized, and the daily urinary excretion of HGA decreased by 2-3g. This case illustrates the critical role of renal tubular secretion in eliminating HGA from the body, and suggests that renal transplantation in a uremic patient not only restores HGA excretion, but may also provide homogentisate 1,2-dioxygenase activity for the metabolism of HGA.

Alkaptonuria in Slovakia: thirty-two years of research on phenotype and genotype

Research on alkaptonuria (AKU; OMIM # 230500) in Slovakia started in 1968 by the Research Laboratory (later on the Institute) for Clinical Genetics at Martin. Its first stage was focused on clinical, biochemical, genetic and epidemiologic questions and on the reasons for the high prevalence of AKU in Slovakia. Based on a screening programme of now over 611,000 inhabitants (509,000 newborns) the world-wide highest incidence of AKU (1 in 19,000) was recorded, and a total of 208 patients (110 children) were registered. Extensive genealogical studies (sometimes over two centuries) resulted in the fusion of several "unrelated" nuclear families into larger pedigrees and enabled tracing most AKU ancestors to their original geographic localities, predominantly in remote mountain areas. A likely founder effect was detected among the shepherd population of the so-called Valachian colonization that resulted in a high degree of inbreeding and persisting genetic isolation. These epidemiologic data formed the basis for molecular studies in collaboration with the Würzburg group. The AKU locus was mapped to human chromosome 3q2 by orthology to the mouse locus aku. Following the cloning of the homogentisate-1,2 dioxygenase (HGD) genes from human and mouse, nine different mutations were identified in 21 AKU index patients. These include 4 missense, 2 splice-site, 2 single-base insertion and 1 deletion mutation. The most frequent mutations among the 42 AKU chromosomes of the index cases are c.648G > A (Gly161Arg; 42.9%), and c.1278insC (Pro370fs; 19.1%). To date, the genotypes of 29 patients and of 74 gene carriers from 21 families have been established. The highest prevalence and allelic heterogeneity were observed in the Kysuce district with five different mutations. Molecular epidemiology studies by haplotyping were carried out to uncover the original geographic localities of all AKU index chromosomes. This strongly suggests that several founders have contributed to the HGD gene mutation pool. While there is no straightforward explanation for the clustering of independent mutations, the genetic isolation in the past is likely to be responsible for the high prevalence of AKU in Slovakia.