Musculoskeletal manifestations in Alkaptonuria: A cross-sectional study

This study aimed to determine the patient characteristics and clinical presentation of Alkaptonuria cases reported by the Biochemical Genetics Lab.An observational study was conducted at the Biochemical Genetics Lab. Alkaptonuria patients were diagnosed based on the homogentisic acid peak in urine and their demographics and clinical data collected from to 2013 to 2019. Clinical history related to joint diseases, ochronotic presentation, and urine darkening on standing was collected.During 7 years, 21 Alkaptonuria cases were reported from BGL; mean age 19.4 ± 24.5 years (range 0.2-66 years) and male to female ratio of 2:1. Of the total, only 9 were adults (mean age, 44 ± 12 years). Most adult patients had musculoskeletal involvement, with joint pain (n = 9) and ochronotic pigmentation (n = 6), whereas all patients presented with a history of urine darkening on standing (21/21 cases).The high prevalence of musculoskeletal involvement observed in patients with albuminuria is likely to be missed by physicians unless specifically tested for in such cases.

Nitisinone arrests ochronosis and decreases rate of progression of Alkaptonuria: Evaluation of the effect of nitisinone in the United Kingdom National Alkaptonuria Centre

QUESTION

Does Nitisinone prevent the clinical progression of the Alkaptonuria?

FINDINGS

In this observational study on 39 patients, 2 mg of daily nitisinone inhibited ochronosis and significantly slowed the progression of AKU over a three-year period.

MEANING

Nitisinone is a beneficial therapy in Alkaptonuria.

BACKGROUND

Nitisinone decreases homogentisic acid (HGA), but has not been shown to modify progression of Alkaptonuria (AKU).

METHODS

Thirty-nine AKU patients attended the National AKU Centre (NAC) in Liverpool for assessments and treatment. Nitisinone was commenced at V1 or baseline. Thirty nine, 34 and 22 AKU patients completed 1, 2 and 3 years of monitoring respectively (V2, V3 and V4) in the VAR group. Seventeen patients also attended a pre-baseline visit (V0) in the VAR group. Within the 39 patients, a subgroup of the same ten patients attended V0, V1, V2, V3 and V4 visits constituting the SAME Group. Severity of AKU was assessed by calculation of the AKU Severity Score Index (AKUSSI) allowing comparison between the pre-nitisinone and the nitisinone treatment phases.

RESULTS

The ALL (sum of clinical, joint and spine AKUSSI features) AKUSSI rate of change of scores/patient/month, in the SAME group, was significantly lower at two (0.32 ± 0.19) and three (0.15 ± 0.13) years post-nitisinone when compared to pre-nitisinone (0.65 ± 0.15) (p < .01 for both comparisons). Similarly, the ALL AKUSSI rate of change of scores/patient/month, in the VAR group, was significantly lower at one (0.16 ± 0.08) and three (0.19 ± 0.06) years post-nitisinone when compared to pre-nitisinone (0.59 ± 0.13) (p < .01 for both comparisons). Combined ear and ocular ochronosis rate of change of scores/patient/month was significantly lower at one, two and three year's post-nitisinone in both VAR and SAME groups compared with pre-nitisinone (p < .05).

CONCLUSION

This is the first indication that a 2 mg dose of nitisinone slows down the clinical progression of AKU. Combined ocular and ear ochronosis progression was arrested by nitisinone.

Old treatments for new insights and strategies: proposed management in adults and children with alkaptonuria

Alkaptonuria (AKU) is caused by deficiency of the enzyme homogentisate 1,2 dioxygenase. It results in an accumulation of homogentisate which oxidizes spontaneously to benzoquinone acetate, a highly oxidant compound, which polymerises to a melanin-like structure, in a process called ochronosis. Asymptomatic during childhood, this accumulation will lead from the second decade of life to a progressive and severe spondylo-arthopathy, associated with multisystem involvement: osteoporosis/fractures, stones (renal, prostatic, gall bladder, salivary glands), ruptures of tendons/muscle/ligaments, renal failure and aortic valve disease. The pathophysiological mechanisms of AKU remain poorly understood, but recent advances lead us to reconsider the treatment strategy in AKU patients. Besides the supporting therapies (pain killers, anti-inflammatory drugs, physiotherapy, joints replacements and others), specific therapies have been considered (anti-oxidant, low protein diet, nitisinone), but clinical studies have failed to prove efficiency on the rheumatological lesions of the disease. Here we propose a treatment strategy for children and adults with AKU, based on a review of the latest findings on AKU and lessons from other aminoacipathies, especially tyrosinemias.

Natural history of alkaptonuria revisited: analyses based on scoring systems

Increased circulating homogentisic acid in body fluids occurs in alkaptonuria (AKU) due to lack of enzyme homogentisate dioxygenase leading in turn to conversion of HGA to a pigmented melanin-like polymer, known as ochronosis. The tissue damage in AKU is due to ochronosis. A potential treatment, a drug called nitisinone, to decrease formation of HGA is available. However, deploying nitisinone effectively requires its administration at the most optimal time in the natural history. AKU has a long apparent latent period before overt ochronosis develops. The rate of change of ochronosis and its consequences over time following its recognition has not been fully described in any quantitative manner. Two potential tools are described that were used to quantitate disease burden in AKU. One tool describes scoring the clinical features that includes clinical assessments, investigations and questionnaires in 15 patients with AKU. The second tool describes a scoring system that only includes items obtained from questionnaires in 44 people with AKU. Analysis of the data reveals distinct phases of the disease, a pre-ochronotic phase and an ochronotic phase. The ochronotic phase appears to demonstrate an earlier slower progression followed by a rapidly progressive phase. The rate of change of the disease will have implications for monitoring the course of the disease as well as decide on the most appropriate time that treatment should be started for it to be effective either in prevention or arrest of the disease.

A quantitative assessment of alkaptonuria: testing the reliability of two disease severity scoring systems

Alkaptonuria (AKU) is due to excessive homogentisic acid accumulation in body fluids due to lack of enzyme homogentisate dioxygenase leading in turn to varied clinical manifestations mainly by a process of conversion of HGA to a polymeric melanin-like pigment known as ochronosis. A potential treatment, a drug called nitisinone, to decrease formation of HGA is available. However, successful demonstration of its efficacy in modifying the natural history of AKU requires an effective quantitative assessment tool. We have described two potential tools that could be used to quantitate disease burden in AKU. One tool describes scoring the clinical features that includes clinical assessments, investigations and questionnaires in 15 patients with AKU. The second tool describes a scoring system that only includes items obtained from questionnaires used in 44 people with AKU. Statistical analyses were carried out on the two patient datasets to assess the AKU tools; these included the calculation of Chronbach's alpha, multidimensional scaling and simple linear regression analysis. The conclusion was that there was good evidence that the tools could be adopted as AKU assessment tools, but perhaps with further refinement before being used in the practical setting of a clinical trial.

Alkaptonuria in France: past experience and lessons for the future

Alkaptonuria (AKU) is an autosomal recessive disorder due to homogentisate 1,2-dioxygenase (HGD) deficiency in the liver and characterized by a triad of signs, according to chronology of appearance: homogentisic aciduria (HGA) or alkaptonuria, ochronosis then ochronotic arthropathy. This inborn error of metabolism is caused by mutations in the HGD gene. In this work we report observations of 96 AKU French patients from 81 families collected in the literature since 1882 and from our personal contribution since 1986, giving an incidence of the disease of around 1:680,000 (96/64.10(6)). As expected for an autosomal recessive disorder the main findings of this study were: a slight predominance of males (51/93, 54,8%) over females (42/93, 45,2%), a strong predominance of sibships with one affected individual (68/81, 84,0%) over sibships with two (11/81, 13.6%) and three(2/81, 2.4%) affected individuals. AKU families are scaterred among the French territory suggesting that most cases occured in non-consanguineous unions. Consanguinity was only found in five families. Other peculiarities of this study were (a) ten of these families have both parents from a foreign geographical origin: Poland(3), Italy(3), Portugal(2), Ukraine(1) and India(1) and four families with only one foreign parent (Algeria, Armenia, Serbia, UK), (b) HGD mutations were found in 23 families, (c) four of theses 96 patients were seen by us respectively 28, 29, 39 and 45 years after their report in the literature and (d) seven patients present cardiac and/or renal complications.

Exogenous ochronosis. An update on clinical features, causative agents and treatment options

Exogenous ochronosis is clinically and histologically similar to its endogenous counterpart; however, it exhibits no systemic effects and is not an inherited disorder. It is characterized by an asymptomatic hyperpigmentation of the face, sides and back of the neck, back, and extensor surfaces of the extremities. The associated ochronotic discoloration most commonly results from use of products containing hydroquinone. It also occurs following use of antimalarials and products containing resorcinol, phenol, mercury or picric acid. The etiology of hydroquinone-induced hyperpigmentation in exogenous ochronosis remains speculative. The majority of patients with this condition are Black, but it has been reported to occur in Hispanics and Caucasians. Exogenous ochronosis is prevalent among South African Blacks, but is believed relatively uncommon within the US. The reasons for this phenomenon are not clear, but it could be a result of the use of skin care products containing resorcinol in combination with hydroquinone or the use of hydroquinone in a hydroalcoholic lotion. Treatment of this condition is difficult. The offending agent must be avoided, but improvement occurs only slowly. A number of topical agents have been studied as have dermabrasion and the use of lasers. Controlled studies in larger numbers of patients are require to determine the true efficacy of newer treatments.

Exogenous ochronosis: an epidemiological study

A survey was conducted to investigate the relationship between exogenous ochronosis and the use of skin lightening preparations amongst black individuals attending general outpatient departments in two South African hospitals. In the sample, 15% of males and 42% of females were found to have exogenous ochronosis. The prevalence amongst users of skin lighteners was 69%. The main demographic associations with ochronosis were an inverse relationship to education, and predominance of the female sex. Clinical and behavioural aspects were also recorded. Even products limited to 2% hydroquinone or less, and combined with a sunscreen, were found to cause ochronosis.

Exogenous ochronosis in the United States

Two middle-aged black women reported hyperpigmentation of the face after using bleaching creams containing hydroquinone. Both noted initial lightening of facial pigmentation followed by progressive darkening of the areas to which the cream was applied. After biopsy, they were found to have exogenous ochronosis. These are the fifth and sixth cases of exogenous ochronosis reported in the United States. In this article we review the literature and discuss the possible pathogenesis of exogenous ochronosis.

Ochronosis in black South Africans who used skin lighteners

Skin-lightening preparations containing hydroquinone are used extensively by black South Africans. In some instances these preparations produce severe and irreversible cutaneous damage. Clinically, the deleterious effects begin with darkening and coarsening of the skin, followed by a hyperpigmented papular condition. Histologically, there is increased basophilia of the collagen, followed by the formation of yellow fibers. These yellow fibers swell and break down to form an amorphous eosinophilic material. Electron microscopy shows that the changes arise from a breakdown of normal collagen.