5 Things You Need to Know about X-Linked Genetic Disorders

Inheritance patterns for genetic disorders generally fall into four categories:

· Autosomal dominant inheritance

· Autosomal recessive inheritance

· Semi-dominant inheritance

· X-linked inheritance

In this article, we examine X-linked genetic disorders and the importance of preconception carrier screening in detecting genetic conditions.

1. X-linked genetic disorders affect males and females differently

We inherit two copies each of virtually all of our genes: one from each parent. The only exception to this comes in the form of X and Y chromosomes. They are the chromosomes that dictate our gender.

A female inherits two X chromosomes: one from each parent. On the other hand, a male inherits an X chromosome from his mother and a Y chromosome from his father.

Genetic diseases are caused by mutations in one or more of our genes. The human body is very resourceful. If one gene copy features abnormalities and the other one is healthy, the body will simply revert to the healthy gene copy. The person will carry the gene mutation and may pass it on, but they will not have the disorder. Due to this principle, females can carry an X-linked genetic disorder without being affected by it.

However, males have no healthy X chromosome to fall back on because they only inherit one copy. When males inherit an X-linked genetic mutation, they inherit the associated disorder.

Females can be born with an X-linked genetic disorder, although to do so each parent would need to pass on the same gene mutation, so this is much more rare.

2. Red-green color blindness is an X-linked genetic disorder

This relatively common genetic condition causes individuals to experience difficulty in differentiating between the colors red and green due to absent or mutated retinal photoreceptors. There are four main types of red-green color blindness:

· Protanopia

· Deuteranopia

· Protanomaly

· Deuteranomaly

Deuteranomaly, which is the most common form of red-green color blindness, affects approximately 0.4% of females and about 6% of males.

3. Other examples of X-linked genetic disorders include hemophilia

Hemophilia A is a blood disorder that interferes with the body’s production of clotting factor VIII, which affects the blood’s ability to coagulate and leads to excessive blood loss. Episodic bleeding can occur externally or internally as a result of trauma or, in severe cases, spontaneously. Bleeding episodes around the joints and muscles can be particularly serious. The disease can also cause potentially life-threatening bleeds on the brain.

Juvenile retinoschisis is an X-linked genetic eye condition. The disease is very rare and occurs almost exclusively in males. Juvenile retinoschisis usually develops in childhood and affects the retina, leading to light-sensitivity issues and blurred vision. Vision can deteriorate throughout childhood and stabilize until late adulthood. People with the disorder can experience a second visual decline, typically in their 50s or 60s.

Fragile X syndrome is a genetic disorder that affects cognitive development and function. The disorder is more common in males, although it can affect females, who usually exhibit milder symptoms. Fragile X syndrome can cause anxiety, impulsive actions, hyperactive behavior, and attention deficit disorder. Physical characteristics of the disease include flat feet, unusually flexible fingers, and a long, narrow face with large ears and a prominent forehead and jaw. Around 5% of females and 15% of males with fragile X syndrome experience seizures.

4. Carrier screening is the only reliable way to determine whether you carry a genetic disorder

Whether a genetic disorder is X-linked, semi-dominant, autosomal dominant or recessive in nature, the only way to effectively deduce whether you are a carrier is to undergo genetic carrier screening.

For many years now, genetic carrier screening has been carried out on expectant mothers as a matter of course to gauge the risk that they may be carrying a child with a genetic disorder. This provides parents and medical professionals with vital genetic insight to make informed decisions, allowing them to formulate effective care plans and prepare for that child’s entrance into the world.

Many parents today take a proactive approach by undergoing preconception carrier screening. By obtaining expert risk analysis ahead of time, parents can avoid the scenario of having to decide whether to continue with a pregnancy where a child is found to be severely affected by a genetic disorder.

5. Even if you find out that you carry a genetic disease, you can still go on to have healthy children

When prospective parents discover that they face a high risk of passing on a genetic disorder, genetic counseling is essential. They can discuss their options with a trained professional.

Pre-implantation genetic diagnosis is a relatively new IVF procedure that facilitates the testing of embryos for genetic disease prior to implantation into the uterus, meaning that even those who carry a genetic disease can have their own natural children.

It is important to remember that carrier screening only detects risk, so even where a high risk is detected, it is not guaranteed that a child will inherit the associated genetic disorder. In X-linked genetic diseases, where a mother is a carrier and gives birth to a son, there is a 50% chance that he will be an affected carrier.

In the vast majority of cases, genetic carrier screening removes doubt, providing prospective parents with vital peace of mind to continue planning one of the most important steps of their lives.