What is the likelihood of a child inheriting factor V (5) Leiden from their mother?

Inheritance Risk of Factor V Leiden from Mother to Child

If a mother has Factor V Leiden, each child has a 50% chance of inheriting the mutation if she is heterozygous (one copy), or 100% chance if she is homozygous (two copies). 1, 2

Understanding the Inheritance Pattern

Factor V Leiden follows an autosomal dominant inheritance pattern, meaning only one copy of the mutated gene is needed to increase thrombotic risk. 1, 2

For Heterozygous Mothers (Most Common Scenario)

• Each pregnancy carries a 50% (1 in 2) chance that the child will inherit the mutation 1
• The mother passes either her normal Factor V gene or her Factor V Leiden mutation to each child independently 2
• Approximately 5% of Caucasian Americans are heterozygous carriers, making this the most likely scenario 1

For Homozygous Mothers (Rare Scenario)

• Each child will inherit Factor V Leiden with 100% certainty 1
• Homozygosity is extremely rare, occurring in only 65 per 100,000 non-Hispanic white individuals 1
• These mothers have two copies of the mutation and can only pass the mutated gene 2

Important Clinical Considerations

Father's Status Matters

• If the father also carries Factor V Leiden (heterozygous), the child has a 25% chance of being homozygous, 50% chance of being heterozygous, and 25% chance of having no mutation 1
• If both parents are heterozygous carriers, each child independently has these same probabilities 2

Genetic Counseling Recommendations

The American College of Medical Genetics emphasizes that patients testing positive should understand that test results have implications about risk in other family members. 1

• Family members should be counseled about their risks and options and considered for testing depending on the overall clinical situation 1
• The laboratory report should explicitly state the risk that other relatives may have the mutation 1

Clinical Implications for Offspring

Children who inherit Factor V Leiden face specific risks:

• Heterozygotes have approximately 10% lifetime risk of venous thromboembolism (VTE) 3
• Homozygotes have over 80% lifetime risk of VTE 3
• The mutation increases VTE risk 4- to 7-fold in heterozygotes and 9- to 80-fold in homozygotes compared to the general population 1

When to Consider Testing Children

Testing should be considered for at-risk family members on an individual basis, particularly when:

• There is a strong family history of thrombotic disease 3
• The child develops thrombosis at a young age 3
• High-risk clinical situations arise (surgery, pregnancy, oral contraceptive use) 1, 3

In the absence of evidence that early diagnosis reduces morbidity or mortality, routine screening of asymptomatic children is not recommended 2