Inherited metabolic disorders

Overview

Inherited metabolic disorders are medical conditions caused by changes in specific genes that affect metabolism. Different gene changes cause different types of inherited metabolic disorders. These gene changes are most commonly passed down from both parents. But sometimes the gene change comes only from one parent, most often from the mother. These disorders also are called inborn errors of metabolism.

Metabolism is the complex set of chemical reactions that your body uses to maintain life. These include:

• Making energy. Special enzymes break down food or certain chemicals so your body can use them right away for fuel or store them for later use.
• Making or getting rid of substances. Certain chemical processes make substances your body needs. Other chemical processes break down substances that your body no longer needs.

When these processes don't work properly, a metabolic disorder occurs. It may be due to an enzyme that's too low or missing or to another problem. Inherited metabolic disorders fall into different groups. They're grouped by the substance affected and whether it builds up too much because it can't be broken down or it's too low or missing.

Symptoms

There are hundreds of inherited metabolic disorders caused by different genes. Symptoms depend on the type of disorder and how severe it is.

Examples of inherited metabolic disorders include:

• Familial hypercholesterolemia.
• Gaucher disease.
• Hunter syndrome.
• Krabbe disease.
• Maple syrup urine disease.
• Metachromatic leukodystrophy.
• Mitochondrial encephalopathy, lactic acidosis, stroke-like episodes (MELAS).
• Niemann-Pick.
• Phenylketonuria (PKU).
• Porphyria.
• Tay-Sachs disease.
• Wilson's disease.

When to see a doctor

If you have concerns about your child's growth and development or your own health, talk to your doctor or other healthcare professional.

Causes

Inherited metabolic disorders are caused by changes in specific genes that affect metabolism. Different gene changes cause different types of inherited metabolic disorders. These gene changes are most commonly passed down from both parents. But sometimes the gene change comes only from one parent, most often from the mother. There are hundreds of inherited metabolic disorders caused by different genes.

Risk factors

The risk of an inherited metabolic disorder is higher if one or both parents have the gene change that can cause the condition. In some cases, future parents may decide to have carrier testing before pregnancy. This test can identify some gene changes in parents that may raise the risk that future children will have certain types of inherited metabolic disorders.

Diagnosis

Some inherited metabolic disorders may be diagnosed before birth. Others can be diagnosed by routine newborn screening tests done at birth. Others are identified only after a child or adult shows symptoms of a disorder.

To find out if you or your child has an inherited metabolic disorder, you may have:

• Physical exam. You may have a physical exam and talk about your or your child's symptoms and medical history. You also may be asked about any family history.
• Tests. Blood and urine tests check to see how the metabolism is working. Sometimes other types of tests may be recommended.

• Genetic testing. Genetic testing can identify the type of inherited metabolic disorder you or your child has. If one person in the family has an inherited metabolic disorder, specialists often recommend genetic testing and counseling for other family members as well.

  In some cases, future parents may choose to have carrier testing before pregnancy, also called preconception screening. This test can identify some gene changes in parents that may increase the risk that future children will have certain types of inherited metabolic disorders.

• Genetic counseling. Genetic counseling can include discussion of newborn screening or other genetic testing. Counseling also can include information on the risk of an inherited metabolic disorder for future children.
• Specialist exams. Certain inherited metabolic disorders may increase the risk of other conditions, such as heart, vision or hearing problems. You may be referred to other specialists as needed.

Treatment

Treatment depends on the type of inherited metabolic disorder and how severe it is. Because there are so many types of inherited metabolic disorders, treatment can vary a great deal. A few examples of treatments include special diets, enzyme replacement, vitamin therapy, medicines and liver transplants. Sometimes care begins with a stay in the hospital. For some types of inherited metabolic disorders, there are no treatments currently available.

Inherited metabolic disorders are rare and complex. Depending on the type and severity of the disorder and your or your child's age, you may see several experts in inherited metabolic disorders. These may include specialists in:

• Medical genetics.
• Nutrition.
• Pediatrics and developmental pediatrics.
• Nervous system.
• Endocrine and metabolic disorders.
• Heart and blood vessels.
• Ear, nose and throat (ENT).
• Eyes and vision.
• Digestive system.
• Kidneys.

Life-long care with regular healthcare visits is important to take care of problems early and adjust treatment as needed.