Thursday, May 14, 2009

Heel Stick: Genetic Screening

The Heel Stick test is a genetic analysis performed on newborn babies to screen for potentially fatal genetic disorders.

Why do I need a Heel Stick test for my baby?

Although your living family may not have certain genetic disorders it is not out of the realm of possibility that a recessive gene may have become active in your child. The test can prevent permanent disability, mental retardation and in some cases death.

How are Heel Stick tests performed?

The Heel Stick test is done soon after you child is born, usually within the first 48 hours. Your baby’s heel is pricked and a few drops of blood are taken for analysis; the nurse collects nine or ten drops of blood and ships the sample to a lab to get tested. It is often wise to get your baby tested multiple times in order to produce the most accurate results.What disorders are tested for?

There are five categories of disorders that are screened:

Amino acid metabolism disorders
Babies with amino acid metabolism disorders, as the name suggests, have problems metabolizing certain amino acids. Babies born with amino acid metabolism disorders have missing or defective enzymes that metabolize proteins. The amino acids either are not broken down or the body cannot transport the amino acids into the cells. As a result, amino acids or nitrogen (a component of amino acids) build up in the body to toxic levels. Amino acid metabolism disorders include Phenylketonuria(PKU), Maple syrup urine disease (MSUD), Homocystinuria (HCY), Citrullinemia (CIT), Argininosuccinic academia (ASA), and Tyrosinemia type I (TYR I).

Organic Acid Metabolism Disorders

Babies with organic acid metabolism disorders cannot process certain branched amino acids. Babies born with this disorder do not produce the enzymes or have malfunctioning enzymes that do not break down these amino acids properly. As a result, organic acids build up to toxic level in the body. Some organic acid metabolism disorders that your baby might be screened for are Isovaleric academia (IVA), Glutaric acidemia type I (GA I), and Hydroxymethylglutaric aciduria or HMG-CoA lyase (HMG).

Fatty Acid Oxidation Disorders
Fatty acid oxidation refers to the way your body breaks down fat. Fat is broken down in several steps and requires a number of enzymes. If one of the enzymes in this process is not working properly the body cannot turn fat into energy for the body. The body’s main source of energy is glucose, but if there is no glucose available, your body turns to fat for energy. Babies with fatty acid oxidation disorders have malfunctioning enzymes so their bodies cannot turn fat into energy. Some examples of fatty acid oxidation disorders that your baby might be screened for are Long Chain 3-Hydroxyacyl-CoA Dehydrogenase Deficiency (LCHAD), Medium Chain Acyl-CoA Dehydrogenase Deficiency (MCAD), Short Chain Acyl-CoA Dehydrogenase Deficiency (SCAD), Trifunctional Protein Deficiency (TFP Deficiency), or Very Long Chain Acyl-CoA Dehydrogenase Deficiency (VLCAD).

Hemoglobinopathies and sickle cell disease
Hemoglobinopathies and sickle cell disease are disorders caused by abnormal hemoglogin, a protein in red blood cells that is responsible for transporting oxygen to the body. Babies with these hemoglobinopathies may have problems with red blood cell production resulting in anemia (shortage of red blood cells) or produce abnormally shaped red blood cells that cause problems in blood circulation and damage easily. These disorders include sickle cell anemia, Thalassemia, and Hb S/C disease.

Other disorders

Other disorders your baby might be screened for include Congenital hypothyroidism (a hormone deficiency that causes problems with growth and brain development), Biotinidase deficiency, Congenital adrenal hyperplasia (an endocrine disorder that affects hormone production from the adrenal gland), or Cystic Fibrosis (a life threatening disease that causes mucous secretions in the lungs to become thick causing severe respiratory problems).

If your baby tests positive during the Heel Stick screening you will need to bring your child in for additional testing. The tests are very sensitive so false positives are a common occurrence. You may need to consult a genetic specialist or pediatrician to entirely diagnose your child.

1 comment:

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