Acta Fac. Pharm. Univ. Comen. LXI, 2014 (1), p. 29–35
ISSN 1338-6786 (online) and ISSN 0301-2298 (print version)
DOI 10.2478/afpuc-2014-0001
ACTA FACULTATIS PHARMACEUTICAE UNIVERSITATIS COMENIANAE
ALKAPTONURIA AND OCHRONOSIS – EXPERIENCE FROM SLOVAKIA
ALKAPTONÚRIA A OCHRONÓZA – SKÚSENOSTI ZO SLOVENSKA
Original research article
Rovenský, J.1, Urbánek, T.1, Imrich, R.2
1
National Institute of Rheumatic Diseases, Piešťany, Slovak Republic
Center for Molecular Medicine, Institute of Experimental Endocrinology,
Slovak Academy of Sciences, Bratislava, Slovak Republic
2
/
Národný ústav reumatických chorôb, Piešťany, Slovenská republika
Centrum molekulárnej medicíny, Ústav experimentálnej endokrinológie, Slovenská akadémia vied, Bratislava, Slovenská republika
1
2
Received February 14, 2014, accepted April 2, 2014
Abstract
Alkaptonuria is a rare inherited genetic disorder of phenylalanine and tyrosine metabolism. This is an autosomal recessive condition that is caused due to a defect in the enzyme homogentisate 1,2-dioxygenase, which participates in the degradation of
tyrosine. As a result, homogentisic acid and its oxide accumulate in the blood and are excreted in urine in large amounts. The
polymer of homogentisic acid called alkapton impregnates bradotrophic tissues.
Slovak
abstract
Alakptonúria je zriedkavé hereditárne ochorenie, ktoré je spôsobené poruchou metabolizmu fenylalanínu a tyrozínu. Je to autozomálne recesívne ochorenie spôsobené defektom enzýmu 1,2-dioxygenázy, ktorá sa podieľa na degradácii tyrozínu. Výsledkom
je, že kyselina homogentisová a jej oxid sa akumulujú v krvi a sú vylučované močom. Polymér kyseliny homogentisovej, ktorý sa
nazýva alkaptón, impregnuje bradytropné tkanivá.
Keywords
Kľúčové
slová:
alkaptonuria; ochronosis; homogentisic acid in urine
alkaptonúria; ochronóza; kyselina homogentisová v moči
DEFINITION
Alkaptonuria is an inherited disorder of metabolism of aromatic amino acids phenylalanine and tyrosine that is caused
due to the lack of activity of the enzyme homogentisate
1,2-dioxygenase (HGD). The homogentisic acid is not metabolised – it accumulates in the body and is excreted into
urine. The polymer – the ochronotic pigment – impregnates
bradytrophic tissues.
CLINICAL SIGNS
Alkaptonuria is characterised by:
• homogentisic acid accumulation in the body
• presence of homogentisic acid in urine
• visible, functionally benign symptoms of eyes and ears
• debilitating changes in the locomotor system.
HISTORY
Scientists found alkaptonuria in the Egyptian mummy
Harwa dated to around 1500 BC. The name alkaptonuria
was first used in 1859 in a patient whose urine contained
a reducing compound (alkapton) later identified as the homogentisic acid. In 1902, Garrod postulated a hypothesis that
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© Acta Facultatis Pharmaceuticae Universitatis Comenianae
alkaptonuria is an inherited metabolic disease and that deficiency of the enzyme that metabolises homogentisic acid is a
result of a defective gene. This concept was later proved correct. His article about alkaptonuria was published in Lancet in
1902 (Garrod, 1902). At that time it was a bold statement when
one considers how little was known about enzymes, human
genetics and intermediary metabolism. His knowledge was
later summarised in his book Inborn Errors of Metabolism (Garrod, 1909). In 1958, the study by La Du et al. provided a biochemical evidence of the defect in alkaptonuria (La Du et al.,
1958). They demonstrated the absence of homogentisic acid
metabolising enzyme activity in liver homogenates from a
patient with alkaptonuria. He found that the defect is related
to one enzyme – 1,2-dioxygenase of the homogentisic acid.
He suggested that the people affected do not synthesise the
enzyme. The gene responsible for alkaptonuria was identified
in 1993 by Pollak et al. and it was localised to chromosome
3q2 (Pollak et al., 1993). In alkaptonuria, the homogentisic
acid is not broken down due to the lack of enzyme activity
that metabolises the homogentisic acid; it accumulates in
the body and is excreted in the urine. The homogentisic acid
builds an oxidised polymer in the body, which is stored in the
form of blue-black deposits in tissues (ochronosis).
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Acta Fac. Pharm. Univ. Comen. LXI, 2014 (1), p. 29–35
ALKAPTONURIA AND OCHRONOSIS – EXPERIENCE FROM SLOVAKIA
AETIOLOGY AND PATHOGENESIS
Phenylalanine and tyrosine are the simplest aromatic amino
acids derived from alanine. Phenylalanine is an essential amino acid that cannot be synthesised by our body. This is not
true for tyrosine. The body can synthesise tyrosine, but only
if there is sufficient amount of phenylalanine – a precursor of
tyrosine and the enzyme involved in the conversion of phenylalanine to tyrosine. Phenylalanine and tyrosine are closely
related; phenylalanine is converted to tyrosine in the liver and
to phenylpyruvate in the kidneys. Aromatic amino acids have
a common intermediary metabolism. The conversion of phenylalanine to tyrosine and further metabolism are controlled
by a complex enzymatic system. The failure to convert phenylalanine to tyrosine is known as phenylketonuria – one of
the most common recessive inborn diseases (approximately
1 affected in 10 000 newborns). Phenylketonuria is caused
by the lack of the enzyme phenylalanine hydroxylase, which
converts phenylalanine to tyrosine or its cofactor tetra­
hydrobiopterrine. Alkaptonuria arises as a result of the lack of
another enzyme – 1,2-dioxygenase of the homogentisic acid
(homogentisate 1,2-dioxygenase; HGD). This enzyme is a part
of the degradation pathway of aromatic amino acids phenylalanine and tyrosine. Homogentisate excreted in the urine
is then oxidised by oxygen in the air to brownish-black pigment – alkapton. Other symptoms later in life include ochronosis – pigmentation of the connective tissue (cartilage). The
mechanism of ochronosis is the oxidation of homogentisate
polyphenoloxidase resulting in the production of benzochinon acetate, which polymerises and binds to macromolecules
of the connective tissue. Exogenous ochronosis results from
prolonged treatment of ulcers with carbol and some other
chemicals. Endogenous ochronosis is due to alkaptonuria.
EPIDEMIOLOGY AND GENETIC ASPECTS
The observation of alkaptonuria inheritance described by
Garrod was studied closely by Hogben et al. (1932) who confirmed that alkaptonuria is inherited in an autosomal recessive manner. They found that about half of the affected individuals came from kin marriages.
The list of scientists who significantly contributed to the
knowledge of the clinical manifestations of alkaptonuria and
ochronosis includes Siťaj, Červeňanský, Urbánek, Hüttl and
others (Siťaj, 1947; Siťaj et al., 1956; Siťaj and Lagier, 1973;
Urbánek and Siťaj, 1955; Červeňanský et al., 1959; Hüttl et al.,
1966). In 1947, Siťaj diagnosed and described the first case of
alkaptonuria (Siťaj, 1947). Till 1953, Siťaj and his team collected a sample of 102 patients – members of 15 families – while
at that time approximately 100 cases were described in the
whole world, mostly isolated case reports. Between 1956 and
1960, they registered other affected families increasing the total number to 28 and the number of patients with alkaptonuria increased to 182, of whom 43 had ochronosis. Slovakia
and the Dominican Republic became known in the literature
30
as the countries where the highest incidence of alkaptonuria
(1 in 19 000 inhabitants) was found. The world prevalence is
one case in 250 000–1 000 000 inhabitants. Increased prevalence in Slovakia is explained by the fact that patients come
from mountainous areas where the population evolved as
genetic isolates with frequent marriages of parents related to
each other. However, it should be noted that the active way of
looking for patients, which has been a tradition in Slovakia for
more than 50 years and dates back to the first case described
by Siťaj, also contributed to the sample size.
Siťaj, Červeňanský and Urbánek described ochronosis, its
development in patients with alkaptonuria and the detailed clinical picture as well as manifestations in the joints
(Siťaj, 1947; Siťaj and Lagier, 1973; Urbánek and Siťaj, 1955;
Červeňanský et al., 1959). They published the results in a
monograph titled Alkaptonuria and ochronosis (1956), which
was the first in the world literature (Siťaj et al., 1956). Their
pioneering work is still being cited. Sršeň et al. from the research laboratory of clinical genetics in Martin followed up
on their epidemiological studies and continued in the genetic analysis of patients with alkaptonuria in Slovakia (Sršeň
and Neuwirth, 1974; Sršen, 1984; Sršeň et al., 1996; Sršeň et al.,
2002). Institutions participating in the molecular characterisation of mutations in the Slovak population include: Institute
of Molecular Physiology and Genetics SAS, Bratislava and
Faculty of Natural Sciences of Comenius University in Bratislava (Zaťková et al., 2000a; Zaťková et al., 2000b; Zaťková et
al., 2000c). Most of the observed families came from sites in
Slovakia studied by Siťaj et al. (Siťaj, 1947; Siťaj et al., 1956;
Siťaj and Lagier, 1973). Later work was continued by Rovenský
and coworkers (Rovenský and Urbánek, 2000; Rovenský and
Urbánek, 2003) and the genetic aspects by Bošák in cooperation with laboratories in Bratislava (Bošák, 2010; Zaťková et al.,
2000a; Zaťková et al., 2000b).
In 1958, La Du with co-workers found that the biochemical
essence of alkaptonuria is the lack of biological activity of the
enzyme HGD in the liver, thus confirming the original assumption of Garrod that it is a metabolic disorder (La Du, 1958).
HGD is an enzyme that is involved in the catabolism of phenylalanine and tyrosine. It has a molecular weight of 50 kDa
and consists of 445 amino acids. It is specific for homogentisic
acid and does not oxidase related substances such as gentisic acid and phenylacetic acid. The gene that encodes the
HGD enzyme was cloned in 1996, thereby opening the era
of molecular genetics of alkaptonuria (Granadino et al., 1997).
We now know that the HGD gene consists of 14 exons (coding parts of the gene) and 13 introns (non-coding part of the
gene). HGD gene has a tissue-specific expression, particularly
in the liver, kidneys, small and large intestine, prostate and
the brain (Fernandez-Canón, 1996). Increased activity in the
liver and kidneys has been attributed to metabolic activity of
these organs. In the brain, HGD probably participates in the
degradation of amino acids derived from neurotransmitters,
which often contain aromatic amino acids. The HGD gene
was localised on the long arm of chromosome number 3 in
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humans (3q) (Pollak et al., 1993; Janocha, et al., 1994). In the
following years, its location on the 3rd chromosome has been
further clarified to the locus 3q21-23 using the technique of
polymerase chain reaction and fluorescent in situ hybridisation (Bošák, 2010).
Molecular genetic studies of alkaptonuria yielded a surprising
finding that the defect of the HGD enzyme is not caused by a
single mutation, as originally expected, but by several mutations in coding and non-coding sequences of the HGD gene.
By 2000, more than 40 different mutations that cause alkaptonuria were identified in more than 100 patients from several countries around the world (Porfirio et al., 2000; Zaťková
et al., 2000). Currently, there are at least 67 known mutations.
Most mutations change the sense of the genetic information
(missense), which involves changing one nucleotide in the
DNA molecule. The most common mutation in Europe, which
represents about 20% of all mutations, is Met368Val (substitution of methionine instead of valine at position 368); in
the Dominican Republic, it is Cys120Trp; and in Slovakia, it is
IVS5 +1G→A (Bošák, 2010).
THE CLINICAL PICTURE
The first signs of alkaptonuria can even be seen in the newborn. Their urine darkens when exposed to the air and leaves
brownish black spots on their diapers. The spots are highlighted and cannot be washed away when alkaline soap is
used. The dark earwax is also a characteristic that can be seen
after birth. Dark urine and ear wax remained the only clinical
symptoms of alkaptonuria for many years. In the meantime,
a much more serious process takes place in the organism affected by this metabolic disorder. The ochronotic pigment is
produced by oxidative polymerisation of the homogentisic
acid; it accumulates in bradytrophic tissues and stains them
dark brown. In principle, it is a benign process, which goes on
unnoticed for a long time.
The first signs of deposition of the ochronotic pigment can be
detected accidentally during professional examination of the
anterior segment of the eye. The ochronotic pigmentation of
the ocular structures is present in approximately 70% of patients. In addition to the sclera, lumps of the ochronotic pigment can be found in the conjunctiva and cornea. Since similar pigmentation of the cornea is not present in other medical
conditions, this finding is regarded as pathognomonic for
alkaptonuric ochronosis. Skinsnes described a patient who
underwent enucleation of his only eye (the other one was lost
due to injury) due to a pigment stain in the sclera deemed as
melanosarcoma (Skinsnes, 1948). After an unrelated death of
the patient, however, the autopsy revealed that this was an
alkaptonuric ochronosis with ocular pigmentation. Pigment
spots on the sclera are mostly visible. They appear usually in
the third decade of life in two-thirds of patients with alkaptonuric ochronosis. In the advanced stage, they can be seen
with the naked eye. When found, chronic poisoning with
phenolic substances, arsenic and lead, Addison’s disease, and
blue sclerae in osteopsatyrosis should be excluded. The diagnosis of alkaptonuria is based on the characteristic findings in
urine. Alkaptonuria patients do not seek medical help due to
difficulties with viewing these spots – they are without subjective complications.
In parallel with the ocular manifestations, ochronotic changes can be found in the hearing organ. Colour changes of the
auricle are visible in the 10th to 15th year of life. Detailed histological examination of the temporal bone performed by
Brunner revealed accumulation of the ochronotic pigment
in the bone and its membranous parts (Brunner, 1929). The
changes taking place in the ears are slow and patients are
alerted to the blue-grey colour of the ear by their relatives.
On the cartilage, painless, hard, rough lumps can be seen
firmly connected with the basis and shining through the
delicate skin as dark-blue-violet colour. The first rough ridges
appear on the lower arm of the anthelix, and later throughout the anthelix, in the fossa triangularis, cavum conchae,
cymbal and the tragus. In advanced cases, sometimes auricle deformation can be found. The external auditory canal is
without changes, earwax is dark brown, drum is dark, dull,
often inverted, with an atypical reflex, with bluish tint, and
in most cases calcium incrustations are present. Patients may
also suffer from hearing loss type hypoacusis mixta with a
stronger involvement of the perceptive apparatus. Symptoms of alkaptonuria hearing organ are specific and often
lead to the diagnosis of this disease.
Also, changes in the skin typical of alkaptonuric ochronosis
include mainly brownish or bluish pigmentation of the skin
under the arm, in the face, neck and hands, and rarely on the
nails. Given their visibility, they may be relevant for the early
diagnosis of alkaptonuric ochronosis.
Ochronotic pigment is deposited also in the internal organs.
In the field of cardiovascular organs, it is the myocardium and
blood vessels. Statistically significant myocardial disorders
were not found, but earlier atherosclerotic changes in the
aorta were observed. Urolithiasis was found in more than half
of the patients and rare cases of nephropathy were seen.
From a clinical point of view, the most serious process takes
place in the joints and is called ochronotic arthropathy. Basically, it is a degenerative process with a known genesis and
with an increased risk of disability. The basic clinical manifestation of ochronotic arthropathy from the beginning is
related to the spine. The first subjective difficulties appear at
the end of the third decade of life. Gender is significant with
a predominance of men relative to women 2:1. Objective
findings include flattening of thoracic kyphosis and lumbar
lordosis, mild rigidity with a tendency to deterioration. Later,
in an advanced stage, the contours of the spine worsen with
irregular spinous processes and complete ankylosis of the entire lumbar and thoracic spine. The spine is rigid, irregular and
the contours do not change when bending forward. Cervical
spine maintains its mobility for a relatively long time despite
significant sciagraphic changes. In an advanced stage, dorsal
flexing and rotational movements become limited, while the
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head moves forward. As a result of degenerative changes to
the plates in the narrowing intervertebral space, body height
decreases up to 8 cm in 20 years.
Using X-ray of the spine, characteristic calcification of intervertebral discs can be diagnosed. Osteolytic and hyperplastic changes and secondary reactive bone formation can
be found on the vertebral bodies. Osteophytes are created,
sometimes even massive bone bridges of the type of ankylosing hyperostosis. Calcification of some peripheral bundles of
the connective rings may be similar to pseudosyndesmotic
bridges. Even in the early stages, hollow formations in the
plates are formed; this is called the vacuum phenomenon.
In the intervertebral joints, the gap is narrowed and reactive
subchondral sclerosis is present.
Sometimes, calcification is found in the ligaments between
the spinous processes. Occasionally, osteoporotic vertebral
fractures are found. On the other hand, thickening of bone
structure is not unusual. This resembles Paget osteitis.
While the spine is affected in all patients with ochronotic
arthropathy, peripheral joints are often, but not always, affected. Based on the analysis of 26 patients with ochronotic
arthropathy, it may be noted that small joints are spared and
large joints are affected in the following order: knee (64%),
shoulders (42.3%) and hips (34.6%).
The finding in the knee is basically of arthritic nature. It differs from genuine osteoarthrosis by an earlier start (average
of 39 years), faster progress and larger deformations. Hydrops
occurred in 30.4% of our patients. Based on a series of investigations, Hüttl et al. have found that the synovial effusion is of
a non-inflammatory, irritating and degenerative nature. The
effusion has a yellowish colour that remains unchanged even
after prolonged standing in air, suggesting a low concentration of homogentisic acid (Hüttl et al., 1966). From the nosographic point of view, it is important to find histiocytes with
brown-violet and blue-black cytoplasmic inclusions, which
can be assumed to be the phagocytosed ochronotic pigment.
The finding of histiocytes with pigment inclusions in the cytoplasm was described by Hüttl et al. for the first time in the
world literature (Hüttl et al., 1966). The X-ray image in ochronotic arthropathy shows similar changes as in osteoarthrosis,
and this is often asymmetric. The characteristic sign is the
formation of free calcified and ossificated pea sized or even
larger bodies of a diverse shape. These are signs of ochronotic
chondromatosis. Occasionally, narrow strips of calcified soft
tissue parts of the extremities are detected that resemble
Thieberg–Weissenbach syndrome. The main difference between genuine arthrosis and ochronosis of the knee is in a
more rapid progression and in advanced findings in relation
to the age of the patient with ochronosis.
In the shoulder joints in the early stages of ochronosis, there
are painful episodes of the type of humeroscapular periarthropathy that are probably related to the deposition of pigment and lime deposits tendons in the rotator. Gradually, the
mobility gets limited due to the retraction of the joint capsule,
destruction of the cartilage and the adjacent bone structures.
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X-ray image of the shoulder joints shows even at an early
stage signs of ossificating enthesopathy. Siťaj proves with an
analysis of 42 patients with ochronosis that the calcareous
deposits in the shoulder rotators are present in more than
25% of patients (Siťaj et al., 1956). In the next stage, around
the 50th year of life, patients develop degenerative changes
with exostosis on the bottom of the joint fossa, and later with
cystoid translucency, usures and destruction on the humerus
head. This finding is completely different from genuine osteoarthrosis and pathognomonic for ochronotic arthropathy of
the shoulder.
The hip joints are affected only in later stages of ochronosis
and approximately in a third of patients. The course is faster
than in coxarthrosis and results in an almost complete restriction of the mobility.
The X-ray examination shows a severe, in some patients,
destructive coxarthrosis. Červeňanský et al. describe ochronotic enthesopathy in the hip area and highlight the selective deposition of the ochronotic pigment in the tendons
(Červeňanský et al., 1959).
Similarity of alkaptonuric ochronosis with other diseases. The
metabolic disorders in ochronotic arthropathy of the spine
and large joints of the limbs include osteoporosis. It is assumed
that this is a secondary form of osteoporosis due to immobilisation of severely affected individuals. Barel et al. describe an
affected family with alkaptonuria, phenylketonuria and congenital cataract (Barel et al., 1960). Occasionally, alkaptonuria
occurs concurrently with psoriasis. In 1955, Urbánek and Siťaj
described a unique coincidence of alkaptonuric ochronosis
and Bechterev’s disease in a 51-year-old man (Urbánek and
Siťaj, 1955). The patient came from a family in which four of
five siblings had ochronotic arthropathy. Based on an analysis
of clinical and X-ray findings in the spine, it could be assumed
that ochronotic arthropathy and Bechterev’s disease interact.
In our patient, typical ochronotic changes were present, especially calcifications of the intervertebral discs, less marked
in comparison with other healthy patients with ochronosis in
advanced disease stages. It may be that the premature rigidity of the spine due to the Bechterev’s disease prevented agerelated development of ochronotic changes. On the other
hand, despite standard Bechterev’s disease symptoms (affected sacroiliac joints, paraspinal ligament ossification and
obliteration of intervertebral joints), the patient had disproportionately low pain throughout the course of the disease.
The long-term observation of a large number of patients with
ochronosis revealed that the relatively subtle pain is characteristic for ochronotic arthropathy (Siťaj et al., 1956).
Japanese authors Kihara et al. described the coexistence of
ochronosis and rheumatoid arthritis in a 64-year-old woman
(Kihara et al., 1994). Magnetic resonance imaging of intervertebral discs found the typical changes suggestive for ochronotic arthropathy. At the same time, symptoms of rheumatoid wrist arthritis were identified with positive rheumatoid
factor and nodules, which histologically were compatible
with the diagnosis of RA. The authors state at the end that the
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pre-existing ochronotic arthropathy could have masked the
manifestation of RA and made it quite difficult to diagnose.
The conclusion of these two case reports is that the process
of ochronosis slows down the development of inflammatory
symptoms of Bechterev’s disease and rheumatoid arthritis
and makes it more benign.
DIAGNOSIS
Diagnosis of alkaptonuria is based on the proof of homogentisic acid in urine. It does not occur in a healthy person. Laboratory evidence of homogentisic acid is based on its reducing
properties. In practise, the test using the Fehling’s solution,
which is used in diabetes, proved valuable. While diabetic
urine with Fehling’s solution brings brick-red clot, alkaptonuric urine changes the colour after the addition of the Fehling’s
solution to grey-black.
For screening, alkalinisation of the urine with 10% NaOH can
be used. After instillation of NaOH to the tube with the urine, a
dark ring is created and then the entire sample of urine darkens.
Earlier quantitative methods for determining homogentisic
acid in the urine used the ability of the acid to reduce silver,
phosphomolybdic acid or iodine. The drawback of these
methods was the fact that they may determine also other reducing compounds present in the urine. This bias appeared
in lower concentration of homogentisic acid in the urine of
patients with alkaptonuria. Certain marked improvement
brought the extraction of homogentisic acid into ether and
subsequent iodometric determination. In 1961, Seegmiller
et al. developed a spectrophotometric enzymatic determination of homogentisic acid in plasma and urine using the
purified homogentisic acid oxygenase, which enabled the
authors to specifically determine 1 µg of the acid (Seegmiller
et al., 1961). The oxidatively produced maleylacetic acid is determined spectrophotometrically at 330 nm. Electrophoretic
method of determining homogentisic acid was established
by Trnavská (1962). At present, the quantitative determination of the homogentisic acid in urine is based on liquid chromatography and capillary electrophoresis.
The diagnosis of ochronosis is based on finding pigment
spots on ocular structures, on the blue-grey discolouration of
the auricles and skin in the armpit and on the X-ray findings
in the calcified intervertebral discs. In the advanced stage of
the disease, irregularly protruding spinous processes of the
thoracic and lumbar spine are typical of ochronotic arthropathy and the finding of pigmented inclusions in the cells of the
synovial effusion is specific.
Differential diagnosis. The fresh urine of a patient with alkaptonuria has a normal pale yellow colour and after prolonged
standing in air or in contact with alkali media (soaps, etc.)
darkens to dark grey to black. This sign of alkaptonuria is specific and it will almost always distinguish it from some other
diseases associated with changes of urine colour. For example, the urine in the hereditary disease congenital erythropoietic porphyriai (m. Günther), which also begins shortly after
birth, has a very typical red colour. Similarly, inhaematuria or
haemoglobinuria urine has a pinkish red colour. The analysis
of the urinary sediment is of decisive importance for the diagnosis. In bilirubinuria, the urine has a reddish-brown colour
(like black beer) and in melanuria a dark brown colour. Urine
is always coloured when it is fresh, with the exception of alkaptonuria, when the urine darkens in contact with the air after
hours or immediately after the addition of alkali.
Ochronosis may be endogenous (on the basis of alkaptonuria)
and exogenous, caused by the contact with certain chemicals.
Several authors have described yellowish pigmentation of the
skin and cartilage caused by carbolic acid (phenol), which was
previously used to treat leg ulcers and other cases. This exogenous “karbolochronosis” was not associated with spondylosis
and arthropathy. More recently, exogenous ochronosis in the
skin and sclera associated with myxedema caused by longterm use of resorcinol was described. Anderson described
the pigmentation of the eye conjunctiva and cornea due to
working in the production of hydroquinone (Anderson, 1947).
The sclera was dark and spots on the cornea caused blindness.
Sugar and Waddell found a pigmentation of the sclera and
cartilage similar to ochronosis after long-term use of atebrin
(Sugar and Waddell, 1946). Skinsnes describes a case of incorrect melanosarcoma diagnosis in a patient with ochronosis
that led to a tragic outcome – enucleation of a single eye of
the patient (see above) (Skinsnes, 1948).
Differentiating ochronotic changes in the spine from other
spondylopathies is crucial to find calcified intervertebral discs,
which are pathognomonic for alkaptonuric ochronosis. Spondylopathies in chondrocalcinosis could cause certain problems in differential diagnosis, but this disease is characterised
by painful process with episodes of attacks of inflammatory
nature, by calcifications of small joints, especially at the wrists,
and the spondylopathy has an easier course with no tendency to ankylosis. In rare cases, a distinction from calcified
discs in hemochromatosis can be considered. When in doubt,
analysis of the urine for the presence of homogentisic acid is
decisive, as well as a comprehensive view of the patient and
evaluation of eye, ear and skin. Alkaptonuric ochronosis has
a characteristic polytope symptomatology that usually does
not cause greater differential difficulties. Rather, it is necessary to exclude other diseases that may require more urgent
intervention before the full clinical picture develops.
THERAPY
As yet, no causal treatment is available for alkaptonuria; therapeutic interventions essentially are in three directions:
-- reduction of the excretion of homogentisic acid into the
urine,
-- restriction of the onset of ochronosis,
-- therapeutic and preventive interventions to influence
ochronotic arthropathy.
In recent decades, various dietary interventions have been tried
to reduce the formation of homogentisic acid and its excretion
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into urine including vitamins, hormones and other substances
with uncertain and in some cases only a transient effect.
When it comes to limiting the production of the ochronotic
pigment and reducing the risk of ochronosis with its disastrous consequences especially on the musculoskeletal system,
a positive effect is attributed to vitamin C (Morava et al., 2003;
Turgay et al., 2009). Some studies, however, did not confirm
the positive effect of vitamin C and there is a lack of long-term
controlled clinical studies targeting this problem (Phornphutkul et al., 2002). Progress in therapy leads to a direct pharmacological reduction of the homogentisic acid. Theoretically, it
would be possible to use nitisinone, a triketone herbicide that
quickly and reversibly binds 4-hydro­xyphenylpyruvate dioxygenase, which catalyses the formation of homogentisic acid
from 4-hydroxyphenylpyruvate. This treatment has, however,
important adverse effects such as increased plasma concentrations of tyrosine and subsequent irritation of the cornea
(Suwannarat et al., 2005). Application of nitisinone in alkaptonuria has so far been experimental.
Alkaptonuria as a congenital metabolic disease is now well
defined. Gene therapy has moved from the phase of model
experiments to the phase of clinical application in humans
and one can hope that prospectively it will be introduced in
the therapy of alkaptonuria. The solution would be the replacement of the missing homogentisate dioxygenase, but
the application of recombinant homogentisate dioxygenase
requires more careful studies of the distribution of isomerase
and other enzymes following the metabolic pathway.
Therapeutic and preventive interventions aimed at influencing ochronotic arthropathy are essentially identical to those
used in the treatment of the degenerative disease of the spine
and limb joints. These include non-steroidal anti-rheumatic
drugs, physical therapy, rehabilitation with balneotherapy,
prevention of the creation of deformities and rheumosurgical interventions if needed. The follow-up of all newborn children diagnosed with alkaptonuria, their constant monitoring,
diet and life style guidance, proper selection of sports and
especially a suitable profession are very important.
In this regard, the research and practise of the workgroup
of Prof. Sršeň at the Medical faculty of the Comenius University in Martin are of particular importance. In children with
alkaptonuria, mild restriction of daily intake of proteins rich
in phenylalanine and tyrosine, as well as the application of
ascorbic acid supplemented with vitamins E, A and selenium
is recommended. In addition, the recommendations include
a daily regimen saving the sites predilected to be affected –
large joints and the spine with corresponding selection and
implementation of a profession.
Somatic gene therapy is progressing from the phase of experimental models to the stage of clinical application in humans
and one can only hope that treatment will be introduced for
alkaptonuria in the near future.
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