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Recessive Inheritance

Sometimes, both parents need to have a faulty gene in order for defects to be passed on to a child. This is referred to as recessive inheritance. Both Tays-Sachs disease and Cystic Fibrosis are recessively inherited birth defects.

X-Linked

X-linked birth defects are passed from mothers to sons. This is because these genetic defects affect only the X-chromosome. Unlike girls, boys only have one X chromosome; if this X-chromosome is defective, the boy will be born with a genetic defect.

Common Hereditary Birth Defects

Some hereditary birth defects are more common than others. However, the chances of your child having a hereditary birth defect depends upon your own family history.

• Tay-Sachs Disease: Tay-Sachs disease affects your baby's central nervous system, causing seizures, blindness, and dementia. Common in Ashkenazi Jews, the disease is typically fatal. If both parents carry the defective gene, there is a 25% chance your baby will be born with the disease.
• Muscular Dystrophy: Muscular dystrophy is a degenerative muscle disease that causes muscle weakness. Duchenne and Becke's muscular dystrophy is inherited from the mother, with a 50% chance of a son developing the disease.
• Sickle Cell Anemia: Sickle cell anemia is a disorder of the red blood cells, causing fatigue, pain, and other health complications. It is commonly found in people of African American and Latin American descent. Sickle cell anemia is a recessive disorder: if both parents carry the gene, there is a 25% chance of having a child with the disease.
• Fragile X Syndrome: Fragile X syndrome can cause hyperactivity, mental development disorders, and autism. It typically affects more boys than girls, and causes the development of a long face, flat feet, and flexible joints. Fragile X is caused by a repeated DNA sequence, which can be passed down by the father or mother.

Diagnosing Hereditary Birth Defects

It is sometimes possible to diagnose hereditary birth defects before birth. Prenatal testing can successfully identify some genetic birth defects, including:

• Down's Syndrome
• congenital heart defects

Babies are also screened for many of the more common birth defects, including Tay-Sachs and Sickle Cell anemia. Unfortunately, not all birth defects are tested for, so if you have a family history for a specific birth defect, be sure to ask for the proper testing.

Some hereditary birth defects do not appear immediately after birth. Some can take up to 30 years (or more) to manifest. This can make diagnosis difficult and could prolong necessary treatment.

Preventing Hereditary Birth Defects

Hereditary birth defects can be prevented through knowledge and action.

Know Your Medical History

Before you get pregnant, it is important to outline your own medical history as well as that of your partner. You should also inquire about the medical history of the rest of you family. Because hereditary disorders are passed down through families, you may be able to tell if your family is affected by a defective gene.

See a Genetic Counselor

If you are at risk, speak with a genetic counselor. Genetic counselors are knowledgeable about various birth defects and how they are passed down. A genetic counselor will be able to assess your risk of having a baby with a genetic birth defect. She will also be able to make suggestions as to how you should proceed with pregnancy.