Notes on Chromosomal Abnormalities and Genetic Disorders

Chromosomal Abnormalities

• Down syndrome

  • Description: An extra chromosome (trisomy 21) leads to mild to severe mental retardation and physical abnormalities.
  • Treatment: Requires surgery for physical issues, early intervention, infant stimulation, and special learning programs. Hormone therapy can also be effective.
  • Incidence: 1 in 1,900 births at age 20, 1 in 300 births at age 35, 1 in 30 births at age 45, 1 in 600 male births.

• Klinefelter syndrome (XXY)

  • Description: An extra X chromosome can result in physical abnormalities.
  • Treatment: Special education and therapy may be necessary; hormone therapy in childhood can help. More common in males.
  • Incidence: 1 in 2,500 female births.

• Fragile X syndrome

  • Description: An abnormality in the X chromosome can cause mental retardation, learning disabilities, and short attention span.
  • Treatment: Special education and speech therapy are beneficial.
  • Incidence: Not specified but predominantly affects males.

• Turner syndrome (XO)

  • Description: A missing X chromosome in females leads to mental retardation and sexual underdevelopment.
  • Treatment: Hormone therapy during childhood and puberty can assist development.
  • Incidence: More common in females, specific incidence not provided.

• XYY syndrome

  • Description: An extra Y chromosome may result in above-average height without additional issues.
  • Treatment: No special treatment is required.
  • Incidence: 1 in 1,000 male births.

Genetic Disorders Related to Other Conditions

• Cystic fibrosis

  • Description: A glandular dysfunction affects mucus production, impairing breathing and digestion, leading to a shortened life span.
  • Treatment: Physical therapy, oxygen therapy, synthetic enzymes, and antibiotics. Most individuals live to middle age.
  • Incidence: 1 in 2,000 births.

• Diabetes

  • Description: The body fails to produce sufficient insulin, causing abnormal sugar metabolism.
  • Treatment: Insulin therapy is crucial; early onset can be fatal without treatment.
  • Incidence: 1 in 2,500 births.

• Hemophilia

  • Description: A condition that causes delays in blood clotting, resulting in internal and external bleeding.
  • Treatment: Blood transfusions/injections can help reduce or prevent damage.
  • Incidence: 1 in 10,000 males.

• Huntington disease

  • Description: Central nervous system degeneration causes muscle coordination issues and mental deterioration.
  • Treatment: No cure; management of symptoms with medications. Symptoms arise around age 35; death usually occurs within 10 to 20 years after onset.
  • Incidence: Not specified.

• Phenylketonuria (PKU)

  • Description: A metabolic disorder leading to mental retardation if untreated.
  • Treatment: A special diet can maintain average intelligence and a normal lifespan.
  • Incidence: 1 in 10,000 to 1 in 20,000 births.

• Sickle-cell anemia

  • Description: A blood disorder that limits oxygen supply and can result in joint swelling, heart, and kidney failure.
  • Treatment: Penicillin, pain management medication, and blood transfusions are common.
  • Incidence: 1 in 400 African American children (less common in other ethnic groups).

• Spina bifida

  • Description: A neural tube disorder leading to brain and spine abnormalities.
  • Treatment: Corrective surgery at birth, orthopedic devices, and various therapies are recommended.
  • Incidence: 2 in 1,000 births.

• Tay-Sachs disease

  • Description: A genetic disorder where lipid accumulation in the nervous system leads to mental and physical decline.
  • Treatment: Medication and diet help manage the condition, but death is likely by age 5.
  • Incidence: 1 in 30 American Jews are carriers; general incidence not specified.