Which enzyme is defective in people with alkaptonuria

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 condition is very rare. The parents of a person with alkaptonuria will often only carry one copy of the faulty gene themselves, which means they will not have any signs or symptoms of the condition.

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. Read about living with pain. 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 affect quality of life. This enzyme helps break down the amino acids phenylalanine and tyrosine, which are important building blocks of proteins.

Mutations in the HGD gene impair the enzyme's role in this process. As a result, a substance called homogentisic acid, which is produced as phenylalanine and tyrosine are broken down, accumulates in the body. Excess homogentisic acid and related compounds are deposited in connective tissues , which causes cartilage and skin to darken. Over time, a buildup of this substance in the joints leads to arthritis.

Homogentisic acid is also excreted in urine, making the urine turn dark when exposed to air. This condition is inherited in an autosomal recessive pattern , which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Genetics Home Reference has merged with MedlinePlus. Learn more. The information on this site should not be used as a substitute for professional medical care or advice.

Contact a health care provider if you have questions about your health. From Genetics Home Reference. Description Alkaptonuria is an inherited condition that causes urine to turn black when exposed to air. According to an observational study in , couples, there was a 35 percent increase in the chance of birth defects in newborns if the father…. Krabbe disease is a rare and life threatening disorder of the nervous system.

Sturge-Weber syndrome is a rare neurological disorder present at birth. Learn about its symptoms, causes, diagnosis, and treatment. Health Conditions Discover Plan Connect. Medically reviewed by Alana Biggers, M. What are the symptoms of alkaptonuria? What causes alkaptonuria? How is alkaptonuria diagnosed?

How is alkaptonuria treated? What is the outlook for alkaptonuria? Read this next. Phthisis Bulbi. Medically reviewed by Ann Marie Griff, O. Heart Valve Disorders. Medically reviewed by Gerhard Whitworth, R.

Medically reviewed by Dr. Payal Kohli, M. What Is Caudal Regression Syndrome? Medically reviewed by Mia Armstrong, MD. Krabbe Disease. Medically reviewed by Heidi Moawad, M. Sturge-Weber Syndrome.