Each cell in the body contains 23 pairs of chromosomes. These carry the genes you inherit from your parents.
One of each pair of chromosomes is inherited from each parent, which means (with the exception of the sex chromosomes) there are two copies of each gene in each cell.
The gene involved in alkaptonuria is the HGD gene. This provides instructions for making an enzyme called homogentisate oxidase, which is needed to break down homogentisic acid.
You need to inherit two copies of the faulty HGD gene (one from each parent) to develop alkaptonuria. The chances of this are slim, which is why the disease is very rare – affecting just 1 in 250,000 to 500,000 people worldwide, and only around 64 people in total in the UK.
The parents of a person with alkaptonuria will often only carry one copy of the faulty gene themselves, which means they won't have any signs or symptoms of the condition.
How alkaptonuria is managed
Alkaptonuria is a lifelong condition – there's currently no specific treatment or cure.
However, a medicine called nitisinone has shown some promise, and painkillers and lifestyle changes may help you cope with the symptoms.
Nitisinone is not licensed for alkaptonuria – it's offered "off label" at the National Alkaptonuria Centre, the treatment centre for all alkaptonuria patients based at Royal Liverpool University Hospital.
Nitisinone reduces the level of homogentisic acid in the body. It's currently an experimental treatment, but research into its effectiveness is ongoing and there have been some promising results so far.
If the condition is diagnosed in childhood, it may be possible to slow its progression by restricting protein in the diet, as this may reduce levels of tyrosine and phenylalanine in your body.
A low-protein diet can also be useful in reducing the risk of potential side effects of nitisinone during adulthood. Your doctor or dietitian can advise you about this.
If alkaptonuria causes pain and stiffness, you may think exercise will make your symptoms worse. But regular gentle exercise can actually help by building muscle and strengthening your joints.
Exercise is also good for relieving stress, losing weight and improving your posture, all of which can ease your symptoms.
The AKU Society recommends avoiding exercise that puts additional strain on the joints, such as boxing, football and rugby, and trying gentle exercise such as yoga, swimming and pilates instead.
Your GP or a physiotherapist can help you come up with a suitable exercise plan to follow at home. It's important to follow this plan as there's a risk the wrong sort of exercise may damage your joints.
Speak to doctor about painkillers and other techniques to manage pain. You may want to try transcutaneous electrical nerve stimulation (TENS), where a machine is used to numb the nerve endings in your spinal cord and reduce pain. This treatment is usually arranged by a physiotherapist.
A diagnosis of alkaptonuria can be confusing and overwhelming at first. Like many people with a long-term health condition, those who find out they have alkaptonuria may feel anxious or depressed.
But there are people you can talk to who can help. Talk to your GP if you feel you need support to cope with your illness. You could also visit the AKU Society website, a charity offering support to patients, their families and carers.
Sometimes surgery may be necessary if joints are damaged and need replacing, or if heart valves or vessels have hardened.
People with alkaptonuria have a normal life expectancy. However, they will usually experience severe symptoms, such as pain and loss of movement in the joints, which considerably impact on quality of life.
Working and carrying out strenuous physical activity will usually become very difficult, and eventually you may need mobility aids such as a wheelchair to get around.
Visit the AKU Society website for more information and support.
Information about you
If you or your child has alkaptonuria, your clinical team will pass information about you/your child on to the National Congenital Anomaly and Rare Diseases Registration Service (NCARDRS).
This helps scientists look for better ways to prevent and treat this condition. You can opt out of the register at any time.