LESSON 12: Genetic Diseases

• achondroplasia (dwarfism) - phenotypes primarily genetically determined
• mental retardation in persons with phenylketonuria - phenotypes require genetic and environmental factors
• lead poisoning - result primarily from the environment or chance
• Types of Genetic Disorders

  1. chromosomes and chromosome abnormalities
  2. single gene (monogenic) disorders
  3. polygenic disorders
• hereditary mutation - mistake that is present in the DNA of virtually all body cells

  • also called germline mutations because the gene change exists in the reproductive cells and can be passed from generation to generation
• Down Syndrome - caused by non-disjunction of the 21st chromosome

  • the individual has a trisomy (3-21st chromosomes)
• Klinefelter’s Syndrome - disorder occurring due to non-disjunction of the X chromosome

  • the egg may contribute the extra X chromosome (XXY)
• XXY Individuals Characteristics

  • males with breast tissue development
  • little body hair
  • infertility
  • mental retardation may or may not be present
• Turner’s Syndrome (45, X) - associated with underdeveloped ovaries, short stature, webbed and is only in women

  • bull neck and broad chest
  • sterile, lack expected secondary sexual characteristics
  • mental retardation typically not evident
• Sickle Cell Anemia - an inherited, chronic disease in which the red blood cells, normally disc-shaped, become crescent-shaped
• sickle cell pain crises - blood clots that give rise to recurrent painful episodes
• sickle cell anemia - normocytic or normochromic

  • most commonly found in African American populations
  • discovered over 80 years ago
• Cystic Fibrosis - monogenic; caused by a deletion of only 3 bases on chromosome 7

  • fluid in lungs, potential respiratory failure
  • overproduction of mucucs
  • common among Caucasians - 1 in 20 are carriers
• Tay-Sach’s Disease - monogenic, autosomal recessive; deficiency in hexoaminidase A

  • central nervous system degrades, ultimately causing death
  • most common among people of Jewish, Eastern europe descent
• Muscular Dystrophy - muscles of the body get weaker and weaker and slowly stop working because of a lack of a certain protein

  • can be passed on by one or both parents depending on the form of MD, therefore, it is autosomal dominant and recessive
• Hemophilia - the “royal” disease; oldest known hereditary bleeding disorder

  • caused by a recessive gene on the X chromosome
  • there are about 20,000 hemophilia patients in the United States
  • severity is related to the amount of the clotting factor in the blood
  • about 70% of affected individuals have less than one percent of the normal amount
• Huntington‘s Disease - inherited degenerative brain disorder which results in an eventual loss of both mental and physical control

  • also known as Huntington’s Chorea
• chorea - “dance-like” movements
• Huntington’s Disease - an autosomal dominant neurodegenerative disorder first clinically described by Huntington in 1872

  • rare, with death rates of 1.6 per million, and is most common among white Europeans
  • initial symptoms occur in those aged 30-50 (can strike in the 20s where suicide is often result)
  • death comes on average 12 years after the onset
• Huntington’s Disease - scientists have discovered that the abnormal protein produced by the Huntington’s disease gene which contains an elongated stretch of amino acids called glutamines, binds more tightly to HAP-1 (huntington-associated protein 1) than the normal protein does
• Phenylketonuria - people with PKU cannot consume any product that contains aspartame

  • a metabolic disorder that results when the PKU gene is inherited from both parents (autosomal dominant)
  • caused by a deficiency of an enzyme (PAH) which is necessary for proper metabolism of an amino acid called phenylalanine