What Is Alkaptonuria?
Alkaptonuria is an inherited condition characterized by the accumulation of homogentisic acid in the body, causing urine to turn black when exposed to air. Homogentisic acid is a toxic substance. The accumulation of homogentisic acid occurs when the body cannot produce enough of an enzyme called the homogentisic dioxygenase. This enzyme is used to break down the toxic substance. When the body cannot produce enough homogentisic dioxygenase (HGD), the homogentisic acid builds up in the body, causing the bones and cartilage to get discolored and very brittle. This condition leads to osteoarthritis, and people also have their urine turning dark brown or black when exposed to the air. Alkaptonuria is known as black urine disease, AKU, or homogentisic acid oxidase deficiency.
What Are the Causes for Alkaptonuria?
Alkaptonuria is an inherited condition that is inherited in an autosomal recessive pattern, meaning that both parents should carry the gene mutation to pass it on to the child. It is caused by a mutation in the homogentisate 1,2 dioxygenase (HGD) gene. This HGD gene offers instructions for the production of the enzyme called the homogentisic dioxygenase. This enzyme breaks down the amino acids phenylalanine and tyrosine, the important building blocks of proteins. The enzyme's role in the process is impaired when there is a mutation or defect in the gene. As a result, the toxic substance homogentisic acid accumulates in the body. Excessive homogentisic acid and other compounds get deposited in the connective tissues causing the cartilage and the skin to darken. And over time, this accumulation of toxic substances in the joints can lead to arthritis. In addition, this homogentisic acid is excreted in the urine, making the urine change its color when exposed to air.
What Are the Symptoms of Alkaptonuria?
Over time the homogentisic acid gradually builds up in the tissues throughout the body. It can accumulate in any body part, including the cartilage, tendons, bones, nails, ears, and heart. It typically stains the tissues and causes various problems. Early signs of alkaptonuria can be seen during childhood, such as dark black stains on the child’s diaper, and the symptoms can become very obvious over age.
Bones And Joints: People with alkaptonuria develop joint problems when they reach their 20s or 30s. They start to experience lower back pain and stiffness, followed by knee, hip, and shoulder pain. Later over age, the bones and cartilages become brittle and break, resulting in joint or spinal damage.
Ears: There will be thickening and bluish-black discoloration of the ear cartilage. This condition is referred to as ochronosis. This is one hallmark sign of alkaptonuria in adults. And even the ear wax can be black or reddish-brown.
Eyes: Most people with alkaptonuria develop brown or gray spots on the whites of their eyes.
Skin And Nails: There can be discoloration of the skin, particularly the areas exposed to the sun and where the sweat glands are located, such as the cheeks, forehead, and armpits. The sweat can also be discolored and can also stain the clothes. Nails can also turn bluish.
Other Symptoms Include:
Deposits of homogentisic acid around the heart valves can cause the hardening of these valves. This hardening can turn the valves brittle and black. The blood vessels also stiffen and weaken over time.
The deposits of homogentisic acid can lead to the formation of kidney stones, bladder stones, and prostate stones.
How Do I Understand If My Condition Is Alkaptonuria?
Doctors usually diagnose the condition by the signs and symptoms reported by the patient. One primary symptom that helps diagnose this condition is changing urine color when exposed to air.
How Is Alkaptonuria Managed?
Alkaptonuria is a long-term and chronic condition, and there is no particular treatment for the condition. However, certain medications and treatment choices help to cope with the symptoms.
Diet: If alkaptonuria is diagnosed at an early stage during childhood, it is possible to slow down its progression by restricting the intake of protein in the diet. Reduced protein intake can reduce tyrosine and phenylalanine levels in the body. This reduced protein intake can also lower the side effects of the medications taken during the treatment.
Exercise: Exercises help improve some of the symptoms of alkaptonuria, such as joint stiffness and pain. Regular and routine exercises help build muscles and also help strengthen the joints. But you have to ensure that the exercises do not strain your joints. If you feel there is additional strain, then avoid such exercises that are putting stress on the joints. Besides this, exercises also help in lowering stress, weight loss, and posture improvement.
Nitisinone: Nitisinone is not approved for alkaptonuria, but currently, Nitisinone is recommended to treat this condition as it is known to reduce the levels of homogentisic acid in the body. At present, this is just an experimental treatment; the evidence of its effectiveness is still underway, and so far, there have been good promising results from this treatment.
Painkillers: Doctors may also recommend a few painkillers to manage pain.
Surgery: In certain cases of alkaptonuria, surgery can be suggested when the joints are damaged and require replacement or in instances when heart valves or blood vessels are hardened. Some of the commonly preferred surgical procedures include:
Emotional Help: Being diagnosed with chronic conditions like alkaptonuria can be emotionally stressful, but anxiety and depression can worsen the symptoms. So taking a doctor’s help is very important for mental health.
Certain symptoms can considerably affect the quality of life. However, people with alkaptonuria can lead a normal life, and life expectancy is fairly normal. In addition, taking appropriate treatment for their symptoms can help delay the complications from the conditions.
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