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How Much Are Cataracts Genetic?

How Much Are Cataracts Genetic?

Are you predestined to get cataracts? Well, due to genetics, you may very well be. Genetics can have an effect on the lens inside our eye and can influence how cataracts develop in that lens.

Cataracts are formed from the natural lens in our eye. Genetic defects in various stages of lens development or function can lead to cataracts. In some cases, known genetic defects lead to the formation of cataracts at birth. But sometimes these genetic defects cause you to be more susceptible to cataract formation over time.

Thus, having family members with cataracts does put you at a higher risk of developing a cataract yourself. This can cause you to develop an age-related cataract at an earlier age. Let's how much of a risk this is.

How Are Cataracts Formed

Within our eye is a lens. This lens is responsible for focusing light and allowing us to see things in focus. When we are young, this lens also gives us the ability to read up close. To do all of this, the lens is one of the few structures in our body which is completely transparent (with the other major one being the cornea).

But gradually over time, this lens gets cloudy. The transparent proteins within the lens called crystallins break down and become less transparent. Most typically this occurs due to age but can happen due to other causes such as with medications, illnesses, or injury.

But how much does genetics play a role in the development of cataracts?

There ARE Purely Genetic Cataracts

There can be genetic defects which lead to the development of cataracts.

In order for the lens to develop and become transparent, many things have to go right.

  1. The lens has to develop properly. If the lens is abnormal from the get-go, it often will result in a cataract.
  2. The lens has to obtain proper nutrients. If the lens cells can't regulate the flow of water or nutrients into the cells, they won't be normal and can get cloudy.
  3. The transparent crystallin proteins of the lens must be normal. It is the unique structure of the proteins which allows it to be transparent. If the protein structure is "off", the protein won't be transparent and the lens will be cloudy.

For each of these steps, specific defective genes have been identified! And for some of these genes, very predictable inheritance can be identified. The genetics of these types of cataracts are very pure. There is a known genetic defect, it causes a failure of the lens to function like it normally should and a cataract develops.

But chances are if you have one of these cataracts, you will already have known about it. Why? Because these cataracts fall into a category called congenital cataracts.

Congenital cataracts are either present at birth or occur very shortly after birth. With these genetic defects, the lens can't maintain transparency very well. And with most of these congenital cataracts, the infant with the cataract must have cataract surgery very early on in life to allow for proper vision development. Thus, if you had a congenital cataract, there's a good chance you have already had cataract surgery to fix it.

Inheritance

Despite these being pure genetic cataracts, it's not a given that you will pass on these cataracts to your children. Everyone has two copies of a gene. One copy came from your mother and one copy came from your father. Depending on what the gene does, genetic issues can be inherited in different ways.

  • There are certain traits which are considered dominant. You only need a single defective copy of the gene. Depending on how many defective copies you have, your child may have a 100% chance of getting a defective copy (if both of your genes are defective) or a 50% chance (if only one of your genes are defective).
  • Other traits are considered recessive. Haven't only one defective copy of the gene won't cause the disease; both copies need to be defective. Thus, this will only pass on to your children if a defective copy comes from both the mom and the dad.

Those are the basic; but inheritance can get more complicated than that. What if, for example, having a defective gene doesn't immediately cause a problem but instead makes your more susceptible to a problem? Well, that is how genetics plays a part in cataracts beyond the congenital stage.

Genetics With Age-Related Cataracts

Cataracts that are purely genetic form at or near birth. There doesn't need to be any environmental influence to cause those cataracts. But genetics can have some role in cataracts beyond that stage.

As mentioned, defects in the ability of the lens cells to regulate the flow of nutrients or in the ability of the crystallin lens proteins to fold can cause cataracts. But what if these defects don't immediately cause a cataract? They are still defects, and instead can make the lens more susceptible to stress. These genes may only cause mild impairment or dysfunction; not enough to push the lens into a cataract but enough to cause issues down the road. This is how genetics affects the development of age-related cataracts.

Certain genetic defects can make you more susceptible to developing a cataract. This can make cataracts occur at an earlier age than what they normally would have. The lens has a harder time responding to stress from the environment, toxins or medical conditions and cataracts can form.

In many of these cases there is no single gene which causes the issue (if it was a single gene, most likely it would cause a congenital cataract instead). Often, the increased risk of cataracts comes from multiple impaired genes. Between this and the late-onset of these types of cataracts less is known about the exact genetics.

But despite not knowing the exact specifics, genetics does play a clear role. In fact, studies amongst siblings and twins have estimated that approximately 50% of the severity of an age-related cataract can be contributed by genetics! Other types of cataracts have a similar genetic composition.

Having a family member with cataracts does make you more likely to develop cataracts.

Summary

Cataracts do have genetic influence. Sometimes this leads to cataracts forming at birth. But more often, this influences how early in life you develop cataracts. Those that have siblings who have developed cataracts at an earlier age are more likely to develop cataracts themselves.

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