Overview of Hereditary Metabolic Disorders

Your body breaks down food you eat into simple chemical building blocks. Then your body uses those building blocks to make other substances your body needs to grow and repair itself. This whole process is called metabolism.

Metabolism is carried out by chemical substances called enzymes. Enzymes are made by cells in your body. Your body makes thousands of different enzymes. Each enzyme carries out only one specific chemical reaction—either breaking down or building a certain substance.

A metabolic disorder happens when your body doesn't make enough of one of the enzymes needed for metabolism. That usually happens because you inherit a defective gene for that enzyme from a parent before you're born. Not having enough of an enzyme causes problems depending on what that enzyme was supposed to do.

• If the enzyme was supposed to break down a certain chemical, that substance builds up in your body

• If the enzyme was supposed to build a certain chemical, then your body doesn't have enough of that substance. Also the chemical building blocks for that substance build up in your body because there's no enzyme to put them together.

Having too little or too much of most chemical substances can cause problems in how your body functions.

• There are hundreds of different hereditary metabolic disorders, but most are rare

• The only way to have a hereditary metabolic disorder is to be born with it

• The disorders may cause symptoms at birth or not until later in infancy

• Babies with a hereditary metabolic disorder may become very sick or even die

• Doctors test for hereditary metabolic disorders during pregnancy if anyone in the parents' families has one of the disorders

• All newborn babies are tested for certain hereditary metabolic disorders

You have 2 genes for each enzyme, one from each of your parents. To have a hereditary metabolic disorder, you need to inherit a defective gene from both your parents. That's because a normal gene from one parent can usually make enough enzyme to keep you from getting sick.

Because there are hundreds of metabolic disorders, there are many different symptoms. However, very often newborn babies have symptoms such as:

• Not eating well

• Throwing up a lot

• Appearing weak and tired

• Having seizures

Later in infancy, babies may not grow and develop normally.

Doctors may test for hereditary metabolic disorders at different times, including:

• Before birth (prenatal testing)

• Right after birth (newborn screening)

• During infancy

Prenatal testing includes checking for genetic disorders with:

• Amniocentesis—doctors take a small sample of the fluid that surrounds the baby when you're pregnant (amniotic fluid)

• Chorionic villus sampling—doctors take a small sample of the organ that grows on the inside of your uterus (womb) when you're pregnant (placenta)

Newborn screening tests use a small drop of your baby's blood to test for hereditary metabolic disorders.

Sometimes doctors may suspect a disorder when examining a child. Then they'll do:

• Blood tests

• Urine tests

If any of these tests show signs of a hereditary metabolic disorder, doctors then do other tests. The tests may include genetic testing and sometimes a biopsy. For a biopsy, doctors take out a small piece of your child’s tissue to look at under a microscope.

Treatment depends on the type of disorder. Many metabolic disorders don't have a specific treatment. Doctors may treat your child with:

• A special diet

• Medicine

• Bone marrow or stem cell transplant

• Dialysis, to get rid of built-up substances in your blood

• Vitamin supplements