Is Lazy eye Inherited from Mom or Dad?

Strabismus, commonly known as "crossed eyes" or "lazy eye," is a condition where the eyes don't align properly. While one eye focuses on an object, the other may turn inward, outward, upward, or downward. It affects around 2–4% of children and can lead to issues like poor depth perception, amblyopia (weakened vision in one eye), and even social or emotional challenges. But is it something passed down from your parents? Let's explore the science behind it.

What Is Strabismus?

Strabismus comes in different forms depending on how the eyes misalign:

• Esotropia: One eye turns inward.
• Exotropia: One eye turns outward.
• Hypertropia/Hypotropia: One eye shifts upward or downward.

It can also be classified as:

• Comitant strabismus: The misalignment is the same in all directions of gaze.
• Incomitant strabismus: The misalignment changes depending on where you look.

Some rare forms of strabismus result from nerve or muscle issues, like congenital cranial dysinnervation disorders (CCDDs), where nerve development is affected. However, the most common type is comitant strabismus, where both eyes can move fully but don't align properly.

Does It Run in Families?

Yes, strabismus often runs in families, but the inheritance pattern is not straightforward. Studies show that genetics play a big role in the development of strabismus, but other factors are also involved. For example:

• Twin studies: Identical twins (who share all their genes) have a 54–82% chance of both having strabismus if one twin is affected. For fraternal twins (who share about half their genes), the chance drops to 14–47%.
• Family studies: About 18–30% of people with strabismus have a close relative with the condition. First-degree relatives (like parents or siblings) have a 3–5 times higher risk of developing strabismus compared to the general population.

This suggests that while genes are important, they don't tell the whole story. Environmental factors and possibly even random chance also play a role.

What Are the Risk Factors?

Aside from family history, several other risk factors can increase the likelihood of strabismus:

• Low birth weight or prematurity.
• Maternal smoking during pregnancy.
• Neurological conditions like cerebral palsy.
• Advanced maternal age.
• Refractive errors like farsightedness (hyperopia) or differences in vision between the two eyes (anisometropia).

Interestingly, some of these environmental factors, like maternal smoking or prematurity, can cause changes in how genes are regulated (through a process called epigenetics), which may link environmental and genetic risks.

What Do We Know About the Genetics?

The genetics of strabismus is complicated. Unlike some diseases caused by a single gene (like cystic fibrosis), strabismus likely involves multiple genes working together. This makes it harder to pinpoint specific genetic causes. Here's what research has found so far:

1. Genome-Wide Association Studies (GWAS)

GWAS look for common genetic variations across large groups of people. Two key genetic regions have been linked to strabismus:

• WRB gene: A variation in this gene on chromosome 21 has been associated with strabismus, and it's more likely to be inherited from the father.
• TSPAN10 gene: Found on chromosome 17, this gene has also been linked to strabismus and other eye conditions, like myopia and astigmatism.

These genetic variations are common in the population and have small effects, meaning they slightly increase the risk of strabismus but don't directly cause it.

2. Copy Number Variants (CNVs)

CNVs are large chunks of DNA that are either duplicated or missing. In one study, researchers found three specific CNVs that significantly increased the risk of esotropia (inward-turning eyes). These duplications were rare but had a large impact, increasing the risk by 8–14 times.

3. Rare Genetic Syndromes

Strabismus is also a feature of several rare genetic syndromes, including:

• Down syndrome: About 33% of people with Down syndrome have strabismus.
• Duane syndrome: A condition where eye movement is limited due to nerve issues.
• Other neurodevelopmental disorders: Strabismus is more common in people with autism or intellectual disabilities.

Do Mom or Dad's Genes Matter More?

Both parents contribute equally to their child's genetic makeup, so strabismus can be inherited from either side of the family. However, some genetic variations, like the one in the WRB gene, may be more likely to be passed down from the father. That said, the overall risk depends on a combination of many genes and environmental factors.

Why Is It So Hard to Identify a Single Cause?

Strabismus is a complex disorder, meaning it doesn't have a single cause. Here's why:

• Genetic diversity: Different families and populations may have different genetic risk factors. For example, esotropia is more common in people of European descent, while exotropia is more common in Asian and African populations.
• Environmental influences: Factors like smoking during pregnancy or premature birth can interact with genetic risks.
• Multiple forms of strabismus: It's unclear whether different types of strabismus (like esotropia and exotropia) share the same genetic causes.

What Does This Mean for Families?

If you or your partner has strabismus, your child may have a higher risk, but it's not guaranteed. The condition is influenced by both genetics and environment, so even if strabismus runs in the family, other factors may determine whether it develops.

For families concerned about strabismus, early screening is key. Treatments like glasses, eye patches, or surgery can improve outcomes, especially if started early.

Conclusion

Strabismus is a condition with a strong genetic component, but it's not as simple as inheriting it directly from your mom or dad. Both genetic and environmental factors play a role, and researchers are still working to understand the exact mechanisms. If strabismus runs in your family, it's worth discussing with an eye doctor, especially for young children, as early intervention can make a big difference.