All you need to know about single gene disorders in babies

Single gene disorders are kinds of abnormalities that happen when a single gene gets mutated during the embryo stage.  Single gene disorders are normally genetic and passed down from a family member. There are many different types of single gene disorders.

Individually, they are usually rare but overall they affect 2% of the population over a lifetime. Learn about the most common single gene disorders in Singapore and what can be done about them.

Common single gene disorders

There are many diseases that are caused by single gene disorders it can hard to keep up with all of them. Many of the regular health problems that people have to deal with everyday can be caused by single gene disorders. They are very common and can affect anyone regardless of race, colour or gender.

In Singapore, the most common single gene defect is that of thalassaemia. Thalasseamia is a genetic blood disorder where your red blood cells not formed correctly and thus not able to carry oxygen.

According to Dr Angeline Lai, Head and Senior Consultant, Genetics Service, Department of Paediatrics, KK Women’s and Children’s Hospital (KKH): “About 5% of our local population, or 1 in 20 persons, is a carrier for thalassaemia.”

Some of the other common diseases caused by a single gene defect include:

Leukaemia – Leukaemia is a cancer of the white blood cells (WBCs). It accounts for about 40% of all childhood cancers in Singapore (about 70-80 new diagnosis yearly).  There have been significant advances in the therapy of childhood leukaemias in Singapore that 60-80% of these children are now long-term survivors and are probably cured.

Retinoblastoma – It is a childhood cancer arising from immature retinal cells in one or both eyes and typically seen between the ages of six months to three years in all races and both genders equally. In general, the incidence is one in 10,000 – 20,000 births, resulting in an average of 2 to 3 new cases every year in Singapore

Muscular Dystrophy (MD) –  a group of muscle diseases characterised by the development of muscle weakness, wasting and contractures, that are usually progressive and sometimes life threatening. MD diseases often manifest in childhood, although some may begin in adulthood. In children, the most common is Duchenne MD, a severe muscle disease which usually only affect boys. The disease occurs in one out of every 3,000 newborn male children.

Cystic fibrosis – an inherited condition that affects the cells responsible for producing mucus. Cystic fibrosis causes the mucus to become too thick, which in turn, blocks up airways. It is a life-threatening disorder that can cause severe damage to vital organs like the the lungs and the gut, resulting in chest infections, poor digestion and absorption.

Haemophilia A –  a bleeding disorder where there is a deficiency of a clotting factor in the blood. This results in a form of bleeding tendency. Thus, the haemophilia patient often suffers from easy bruising and bleeding into muscles and joints. Because of the genetic pattern of inheritance, the disorder generally affects males only. In Singapore, about 200 people are patients of haemophilia.

Why does single gene disorder happen?

Most genetic disorders are due to ancient mutations that first happened a long time ago. Modern science has yet to understand and pinpoint exactly what is the exact cause of these mutations, but because it only involves a single gene, we have made significant progress to detect which babies are more likely to be at risk of having single gene disorders.

Most of us are walking around with between 5 and 10 recessive gene mutations. We don’t get sick because we only have 1 copy of the mutated gene and are just carriers. But, if we make a baby with someone who is also a carrier of that mutation, there’s a 25 % chance the child will get the mutation from both parents and officially have the disorder. That’s the case in illnesses like thalasemmia and cystic fibrosis. There are other genetic disorders in which a child only needs to inherit the genetic mutation from 1 parent.

These gene disorders have no pattern and no preference on which babies they attack. The best protection a parent can offer their baby is opt for early screening, preventative care and prepare a good treatment plan with doctors to offer the best care possible for their baby.

Detecting single gene disorders early

The majority of single gene disorders can only be detected after a baby is born, but there are a few single gene disorders that can be detected beforehand during pregnancy. Early detection of these disorders is key to treating the problem and finding answers about how they form.

There are many gene tests and prenatal screenings that can be done in Singapore to help look for abnormalities in your unborn baby. While some parents may be nervous to take part in these tests, they can be crucial for preventative care and give them ample time to prepare for any needed treatments for the baby.

Genetic screening methods may include the following:

Multiple marker test – This is a blood test that’s used to check your baby’s risk of having problems with the brain and spinal cord (called neural-tube defects) and chromosomal abnormalities, such as Down syndrome. This procedure is done at about between 15 – 20 weeks.

MaterniT21 Plus test – This  is a noninvasive prenatal test (or NIPT) that detects fetal chromosomal abnormalities; from common (trisomies 21, 18 and 13) to the more rare (fetal sex aneuploidies, trisomies 16 and 22, and select microdeletions). This test can be performed as early as 10 weeks’ gestation.

Chorionic villus sampling (CVS) – Chorionic villus sampling involves obtaining some cells from the placenta for testing. This is done during the 10 – 12 weeks of pregnancy.

Fetal blood sampling – Fetal blood sampling involves obtaining a small amount of fetal blood from the umbilical cord for testing. This procedure is done at about 18 – 20 weeks of pregnancy.

Amniocentesis – Amniocentesis involves withdrawing a small amount of the amniotic fluid  surrounding the fetus for testing. This is done by inserting a thin hollow needle through the mother’s abdomen into the uterus. This procedure is done at about 16 – 20 weeks of pregnancy.