Genetic Diseases

• Autosomal Recessive Diseases– PKU (phenylketonuria) caused by a

recessive allele found on Chromosome 12• Causes accumulation of phenylalanine

in brain tissue causing mental retardation

• Early identification leads to modification of dietary intake– Part of the newborn screening program

– Tay-Sachs• Degenerative nervous tissue disease

leading to death in the first year of life– Part of the newborn screening program

Genetic Diseases

• Autosomal Dominant Diseases– Achondroplasia (dwarfism)

• Caused by a missense mutation• Most cases are caused by a new

mutation

– Huntington disease… nervous tissue dissease• Causes loss of muscle control

eventually leading to death in their late 30s

• No part of the prenatal testing

Genetic Diseases

• Codominant Diseases– Sickle cell diseases

• Caused by a single nucleotide substitution in the DNA

• Causes the red blood cells to form a crescent shape (sickle) when oxygen levels are low

• Gives protection against malaria in the heterozygous state

• The carrier is largely unaffected when healthy

– Cystic fibrosis• Most commonly caused by a missing codon in

the gene sequence causing the conformation of the protein to be affected.

• Affected individuals have trouble moving chloride through the cell membranes causing thick pulmonary secretions and digestive problems

• Very low penetrance in the heterozygous state.

Genetic Diseases

• Codominant Diseases (X-linked)– More common in males than females

• Females have 1 X randomly inactivated (called a Barr body)

– Colorblindness• 1 in 10 males• 1 in 100 females

– Hemophilia… clotting disorder– Duchenne Muscular Dystrophy

• Increasing loss of skeletal muscle control leading to eventual death

Genetic Diseases

• Chromosomal disorders– Nondisjunction… failure

of a chromosome to separate during Meiosis

– Trisomy 21 (Down)• 1 in 800 live birth• Common with

increased maternal age

– Turner XO – Kleinfelter’s Syndrome

XXY• Both often lead to

sterility