Genetics: From basics to common diseases

Genetics: From basics to common diseases

# Autosomal Dominant Inheritance

Characteristics:

• Pedigree chart is vertical

• Equal incidence in males and females

• Usually seen in heterozygous genotype

Common diseases:

• Achondroplasia:

• Caused by mutation on chromosome 4

• Manifestations: dwarfism, short limbs, large head, flat nose, prominent forehead, curved spine, normal IQ

• Codominance: lethal in neonates

# Autosomal Recessive Inheritance

Characteristics:

• Enzyme gene

• Equal incidence in males and females

• Pedigree chart is horizontal, not continuous

Common diseases:

• Sickle cell anemia:

• Caused by mutation in the HBB gene, codon 6, replacing A with T, replacing glutamic acid with valine

• Symptoms: anemia, pain, fatigue, shortness of breath, cold hands and feet, pale skin

# X-linked Dominant Inheritance

Characteristics:

• Higher incidence in females than males

• Pedigree chart is vertical, diagonal inheritance: father->daughter, mother -> son

Common diseases:

• Hypophosphatemic rickets:

• Caused by mutation in the PHEX gene on the X chromosome

• Consequences: decreased phosphate absorption in the kidneys, hypophosphatemia, impaired osteoblast activity

# X-linked Recessive Inheritance

Characteristics:

• Disease is more common in males than females

• Pedigree chart is horizontal, generation gap, diagonal inheritance

Common diseases:

• Hemophilia A:

• Caused by mutation in the FVIII gene that encodes coagulation factor VIII on the X chromosome

• Consequences: decreased activity of antihemophilic globulin protein, or decreased production of this protein

# Diseases related to genetic imprinting

• Prader-Willi or Angelman syndrome: deletion of 15q11-15q13, affecting intellectual and physical development.

• Lack of gene from father causes Prader-Willi syndrome: uncontrolled eating, always feeling hungry.

• Lack of gene from mother causes Angelman syndrome: constant laughter, happy facial expressions and excited gestures

# Common diseases of repeat expansion mutations

• Fragile X syndrome: CGG repeats (>= 200)

• Huntington’s disease: CAG repeats (>=40)

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