Infants inherit genetic diseases from parents who are "carriers" of diseases. This occurs because people have two copies of every gene, and many genetic diseases require two abnormal genes to have an effect. People with one mutated gene are called carriers. Other diseases result from chromosomes (large pieces of DNA) not separating properly in sperm or egg cells.
Down Syndrome
As the Genetics Home Reference explains, Down syndrome is a genetic disease caused by the patient having an extra twenty-first chromosome (three copies of chromosome 21 instead of the usual two). This disease affects, on average, one out of every 740 newborns, though the risk of having a baby with Down syndrome increases as the mother's age advances. Patients with Down syndrome typically experience mental retardation, which can range from mild to severe. Many patients also have low muscle tone and a characteristic facial appearance.
Trisomy 13
Trisomy 13 is another genetic disease that results from the infant having an extra chromosome; in this case, the patient has three copies of chromosome 13. According to the Children's Hospital of Wisconsin, children with trisomy 13 often have their two cerebral hemispheres fused, facial deformities (including clefting) as well as congenital heart defects. This condition affects between 1 in 2200 and 1 in 7600 live births, and ninety percent of affected children die within six months.
Fragile X
Fragile X, according to Medline, proves the most common inherited form of mental retardation. Patients with this disease have a defect in a gene that makes a protein that proves critical for the development of the brain. This mutation, which causes the body to make little or no copies of this protein, causes abnormal brain development. Depending on the type of mutation and how much of the protein exists, patients may have severe or virtually unnoticeable mental defects. Patients may also have problems with emotions or social behavior as well as difficulties with language.
Tay-Sachs
According to the National Institute of Neurological Disorders and Stroke (NINDS), Tay-Sachs disease is a genetic condition caused by buildup of a compound called Ganglioside Gm2. This fatty molecule builds up and causes toxicity to cells in the brain, including neurons. Infants who have this disorder initially appear normal but after a few months the ganglioside builds up in their brain, rendering them deaf, blind and unable to swallow. This condition also causes patients to develop a characteristic "cherry-red" spot in their eyes.
