X chromosome
Hemophilia transmission is linked to the X chromosome.
Heredity in hemophilia
How hemophilia is transmitted, why the disease mainly affects boys and why genetic counseling is so important.
Genetic counseling
Helps the family understand risks and options for future pregnancies.
New cases
Some cases appear without family history, through new mutations.
Hemophilia is linked to the X chromosome; therefore the disease mainly affects boys, while girls may be asymptomatic carriers. The genetic information for factors VIII or IX is located on the X chromosome. A mutation on this chromosome prevents proper synthesis of the clotting factor.
Genetic transmission
- Father with hemophilia + healthy mother: all daughters are carriers and sons are healthy.
- Carrier mother + healthy father: daughters have a 50% chance of being carriers and sons have a 50% chance of having hemophilia.
- Sporadic cases: in about 30-40% of cases, the disease appears through new mutations, without family history.
Identifying carriers and genetic counseling are important for family planning and risk assessment in future pregnancies.