Genetic Disorders

What is Genetics?

The study of how traits are passed from parent to child through genes and chromosomes is called genetics. Each cell in your body has pairs of genes and chromosomes that control your physical makeup. Genetic disorders are problems in the genes or chromosomes of a fetus. These disorders may be inherited or they may occur without a family history.

All cells in the body have 46 chromosomes. A man’s sperm and a woman’s egg have 23 chromosomes each. When joined they form the 46 chromosomes of the the cell that will become the fetus.

Each chromosome carries many genes that come in pairs half from the father and half from the mother. Some traits come from a single gene while other traits are the result of many pairs of genes working together.

A gene or a genetic disorder is either dominant or recessive. Dominant genes traits cancel out recessive genes traits. For a recessive gene trait to appear, the gene that carries it must be inherited from both parents.

Types of Genetic Disorders

Dominant Disorders
Dominant Disorders may be passed down from parent to child by one dominant gene. A child has a 1-in-2 chance of inheriting the disorder if one parent has the gene. Examples of dominant disorders are Huntinton’s disease, an inherited nerve disorder that causes loss of control of movements and mental function and Polydactyly, a condition in which a person has extra fingers or toes.

Recessive Disorders
Recessive Disorders can only be passed on if both parents carry the gene. Parents may carry the recessive gene for certain disorders without having the disorder but can still pass it on to their children. If both parents carry the disorder gene, children of those parents have a 1-in-4 chance of having the disorder. Examples of inherited recessive disorders are Sickle Cell disease, a disorder in which red blood cells have a crescent shape causing chronic anemia and episodes of pain, Tay-Sachs disease, a birth defect that causes mental retardation, blindness, seizures, and death, and Cystic Fibrosis, a disorder that causes problems in digestion and breathing.

X-Linked Disorder
X-Linked Disorder are inherited disorders linked to the female X chromosome. In most X-linked disorders, the abnormal gene is recessive. Women may be carriers without having the disorder. Daughter become carriers but sons have a 1-in-2 chance of inheriting the disorder. Sons only inherit one X chromosome which comes from their mother. They do not inherit a second X chromosome with a normal gene to cancel out the abnormal one. Carrier testing may be done to show if you are a carrier of an X-linked disorder. Two examples of inherited X-linked disorders are hemophilia, an disorder in which the blood lacks substance that helps it clot and Duchenne Muscular Dystrophy, a disease that weakens muscles first of the limbs, and trunk, but slowly affects all voluntary muscles usually resulting in death. A third example is Fragile X Syndrome, a disorder that causes mental retardation.

Chromosomal Disorders
Chromosomal Disorders are disorders caused by a missing, damaged, or extra chromosome. Most children with these disorders have physical or mental defects. Examples are Down Syndrome, a disorder resulting from an extra copy of the 21st chromosome in which mental retardation, abnormal features of the fac, and medical problems occur and Trisomy 18, a disorder resulting from an extra copy of the 18th chromosome causing serious physical and mental development. Most infants with Trisomy 18 die within the first year of life.

Multifactorial Disorders
Multifactorial Disorders are disorders that come from a mix of factors. The cause is unknown. A few if detected during pregnancy can be corrected with surgery. An example is Abdonimal Wall Defect, a defect where the muscle and skin that cover the wall of the abdomen are missing and the bowel is either enclosed in a clear sac or sticks out through a hole in the abdominal wall. Other examples are Cleft palate, a disorder where a gap or space occurs in the roof of the mouth, Clubfoot, a disorder where the foot is misshaped and twisted out of position, and Neural Tube Defect, a disorder where there is an incomplete closure of the fetal spine that can result in spina bifida or anencephaly.