Inherited Metabolic Disorders

What are inherited metabolic disorders?

Inherited metabolic disorders affect your body’s ability to convert food into energy and remove waste and unhealthy substances. Some conditions can damage cell development and brain function. Inherited metabolic disorders are also known as hereditary metabolic disorders and inborn errors of metabolism.

Metabolism refers to chemical processes that occur in the body. Your body needs these processes to sustain life. Inherited metabolic disorders occur when abnormal chemical reactions interfere with these processes.

Some inherited metabolic disorders can be detected before birth, or at birth during a routine physical exam. Or symptoms may appear later.

How common are inherited metabolic disorders?

Doctors have identified hundreds of inherited metabolic disorders. Most of these conditions are very rare. Symptoms and treatments will vary greatly for these disorders and diseases.

What are some inherited metabolic disorders?

Among the hundreds of inherited metabolic disorders include:

• Lysosomal storage disorders: Waste products of metabolism are prevented from being broken down, resulting in the buildup of toxins in the body. These include Hurler syndrome, Gaucher disease and Tay-Sachs disease.
• Maple syrup urine disease: A buildup of amino acids results in nerve damage, with a byproduct of the urine having a syrupy smell.
• Glycogen storage diseases: Poor sugar storage causes low blood sugar.
• Mitochondrial diseases: A disorder of mitochondrial cells leads to involvement of many organ system including brain, muscle, liver kidneys etc.
• Peroxisomal disorders: Disorders similar to lysosomal storage disorders and lead to buildup of toxins.
• Metal metabolism disorders: Trace metals build to toxic levels. These include Wilson disease (toxic copper levels) and hemochromatosis (excess iron in the intestines).

What are the risk factors for inherited metabolic disorders?

People at higher risk for inherited metabolic disorders include those who have a family history of the condition.

What causes inherited metabolic disorders?

Defects in genes passed down from your parents cause inherited metabolic disorders. Gene changes can cause a deficiency in hormones or enzymes. These deficiencies cause abnormal chemical reactions that keep the metabolism from working properly.

What are the symptoms of inherited metabolic disorders?

The symptoms of inherited metabolic disorders vary depending on the condition. Some symptoms are mild, while others are debilitating. Some symptoms are:

• Developmental delay.
• Weight loss.
• Growth disorder.
• Seizures.
• Poor appetite and energy levels.
• Unusual odors (such as sweetness) in urine, sweat, breath.
• Pain in the abdomen.

How are inherited metabolic disorders diagnosed?

Doctors diagnose metabolic disorders with screening tests. Blood tests and a physical exam are standard parts of the diagnosis process. With so many inherited metabolic disorders, each kind of testing or screening will be different. The variety of diagnostic tools include:

• Special testing called metabolic testing may be ordered to look at the amino acid (basic building block of proteins), fat and glucose metabolism patterns, to help narrow down diagnosis. Genetic testing can now do this by looking at changes in the genes. These tests may be performed on white cells in the blood or on cells obtained from swabbing inside of the mouth. A genetic specialist can order and interpret these tests.
• Tests for many metabolic disorders can be done prenatally (before a baby is born). In a test called amniocentesis, a sample of amniotic fluid (the fluid surrounding the baby) is removed and examined for abnormalities. The newborn screen, done from a tiny prick on the baby’s heel to draw blood, may give an early warning of a potential metabolic problem.
• Tests for many metabolic disorders can be done prenatally (before a baby is born). In a test called amniocentesis, a sample of amniotic fluid (the fluid surrounding the baby) is removed and examined for abnormalities.
• Sometimes, symptoms of inherited metabolic disorders develop after birth. A doctor may detect these signs during a physical exam. They may include muscle weakness or eye problems.
• Some children may have problems with low glucose (sugar) in blood that lead to lethargy, excess sleepiness or even seizures.
• Some children with specific disorders have enlarged livers, or enlarged livers and spleens. Some may have changes in their facial appearances that may help with diagnosis. Occasionally, an examination of the inside of the eye may help narrow down the diagnosis.

How are inherited metabolic disorders managed or treated?

Treatment is limited because an inherited metabolic disorder is the result of a genetic defect and varies depending on the condition. Many treatments involve changing foods or drugs that can’t be metabolized properly. Some people can take enzyme or chemical replacements to help their metabolism return to close to normal function. Other treatments might be used to remove toxic metabolic byproducts. Gene therapies are all in experimental and early trial phases and aren’t available as routine therapies, but are promising for certain disorders.

What complications are associated with inherited metabolic disorders?

Metabolic disorders have different complications, depending on the condition. Various disorders can cause problems with energy, growth, waste removal from the body and other functions or even seizures.

Can inherited metabolic disorders be prevented?

People with inherited metabolic disorders who want to have children should talk to a genetic counselor. The counselor can help you learn about the risks of passing the condition on to your biological child.

What is the prognosis (outlook) for people with inherited metabolic disorders?

The outlook for people with inherited metabolic disorders varies depending on the condition. Some of the disorders can be life-threatening. But doctors help many people successfully manage the conditions so they can live active, healthy lives.

When should I call the provider?

If you are pregnant, ask your provider about prenatal and newborn screenings for your baby to identify inherited metabolic disorders.

What questions should I ask my provider?

If you have an inherited metabolic disorder, you may want to ask your provider:

• What kind of inherited metabolic disorder do I have?
• What is the outlook for this disorder?
• What does my treatment involve?
• Are there complications I should look out for?
• How will it affect my daily life?
• Is there a support group where I can find other people with this rare condition?

When can I go back to my regular activities?

For many people, inherited metabolic disorders do not interfere with daily activities. Your provider will help you understand when a condition may disrupt your regular activities and when it is safe to return to them.