These genes are found on the X-chromosome, so only men can have the condition because their Y-chromosome cannot override their single X-chromosome.
Women have two X-chromosomes, so if one of them has the mutated haemophilia genes, the other chromosome will override the effect of the genes, making them carriers of the condition.
For these women, their sons will have a 50 per cent chance of inheriting the condition from them.
While haemophilia is usually inherited, it is possible for someone to have the condition without getting faulty genes from his mother, as spontaneous mutations of the genes can occur, said KKH paediatric haematology-oncology consultant Joyce Lam.
Dr Koh Pei Lin, consultant in paediatric haematology-oncology at the National University Hospital, said gene therapy is a potential cure for haemophilia, but this is not yet available as experiments are ongoing.
There is currently no cure, but the condition can be treated with injections of the missing blood-clotting protein.
It is also important to track which joints are most prone to injury - like what the Vazs do with Dominic.
Dr Lam explained that this is because every bleed into a joint causes swelling and makes that particular joint more prone to future bleeds.
Repeated bleeds cause the protective cartilage to break down, and early arthritis sets in. Many haemophiliacs may need a joint replacement by the time they are in their 20s if their bleeding is not well controlled.
According to the Haemophilia Society of Singapore (HSS), there are over 200 haemophiliac patients here.
A spokesman for the Ministry of Health said there have been no deaths from haemophilia in the past five years.
Death can occur when there is severe bleeding or bleeding into vital organs such as the brain, said HSS president Dr Gan Kim Loon.
He added: "In the past, haemophiliacs did not live past 30 years of age.
"However, with today's medical advancement, adequate treatment such as preventive injections of the blood-clotting protein can enable a haemophiliac to engage in physical activities and enjoy a normal life expectancy."
This article was first published in The New Paper.