Some features of X-linked recessive inheritance are:
- only males are affected
- there is no variation in expression, the disorder always follows a typical course
- heterozygous females are clinically unaffected but carry the mutant gene
- only rarely will a female manifest the signs of an X-linked disease; this is usually due to atypical lyonization, a new mutation in the other X chromosome, a carrier with Turner's syndrome, or X-autosome translocation
- milder signs of X-linked disorders may evolve in the female due to normal lyonization
Approximately 290 X-linked recessive conditions are known, the following are the most frequently encountered:
- red-green colour blindness
- non-specific X-linked mental retardation
- Duchenne muscular dystrophy
- Becker muscular dystrophy
- Haemophilia A (factor VIII)
- Haemophilia B (factor IX)
- X-linked ichythyosis
- X-linked agammaglobulinaemia