Leber hereditary optic neuropathy
Determine if the pedigree chart shows an autosomal or X linked disease.
- If most of the males in the pedigree are affected, then the disorder is X-linked
- If it is a 50/50 ratio between men and women the disorder is autosomal.
Determine whether the disorder is dominant or recessive.
- If the disorder is dominant, one of the parents must have the disorder.
- If the disorder is recessive, neither parent has to have the disorder because they can be heterozygous.
- As in autosomal recessive inheritance, two copies of a disease allele on the X chromosome are required for an individual with two X chromosomes (a female) to be affected with an X-linked recessive disease.
- Since males are hemizygous for X-linked genes (they have only one X chromosome), any male with one copy of an X-linked recessive disease allele is affected.
- Females are usually carriers because they only have one copy of the disease allele. Affected males are related through carrier females.
- For a carrier female, with each pregnancy, there is a one in two (50%) chance her sons will inherit the disease allele and a one in two (50%) chance her daughters will be carriers.
- Affected males transmit the disease allele to all of their daughters, who are then carriers, but to none of their sons.
- Women are affected when they have two copies of the disease allele. All of their sons will be affected, and all of their daughters will be unaffected carriers.
ORGAN-BASED X-LINKED RECESSIVE DISEASES
• Alport syndrome (X-linked dominant disease)
• Bruton agammaglobulinemia
• Chronic granulomatous disease of childhood
• Duchenne muscular dystrophy
• Ehlers-Danlos syndrome (certain forms)
• Glucose-6-phosphatase deficiency
• Fragile X syndrome
• Hemophilia A
• Hemophilia B
• Hyper IgM syndrome
• Ocular albinism
• Wiskott-Aldrich syndrome