Family history gets a lot of emphasis in the medical world. The idea is that you can identify health risks and try to reduce them, either through changes in behavior or medical intervention.

A lot of times, family histories are bland and don’t help much with medical care. But, there are some situations where family history really matters a lot.

Family History: The Role of Genetics in Pregnancy

As a geneticist who deals mostly with reproductive genetic issues, I am constantly on the lookout for these situations. One such story came to my attention the other day. I saw a young couple whose two young sons have severe cataracts. Cataract comes from the Greek word for scar. In this case, both boys’ eye lenses were filled with scar-like tissue that made the lenses worse than useless.

The cataracts were present at the time of birth and presumably happened during fetal life. Despite surgical intervention, both boys have severely compromised vision. The couple desired more children, but they were afraid of the risks.

X-Linked Inheritance

Now, it’s pretty strange to have two sons affected with the exact same unusual condition. As I explained to the family, the whole situation sounded like an example of what we geneticists call X-linked inheritance.

The idea is that the mother carries a gene mutation on one of her two X chromosomes. She is not affected because she has the other X chromosome to “cover” for the one with the mutation. When she has kids, there is a 50:50 chance to pass the X chromosome with the mutation to the pregnancy/baby. If a boy inherits the X chromosome with the mutation, he is affected because there is no second X chromosome to “cover.”

As it turns out, there aren’t many known X-linked conditions with cataract as a prominent feature. One of them is called Nance-Horan Syndrome, named after the two doctors who described it. We decided to sequence the patient’s Nance-Horan gene, and discovered that, indeed, she carried a mutation that explained the cataracts in her two sons. When we had the results in hand, we had a long talk about how to go about having another child. The choices are pretty stark, but at least there are choices.

Options for Pregnancy

We discussed three options. One is to have another child and accept the risk that it could be an affected son. The couple rejected this approach immediately. Another way is conventional prenatal diagnosis with the option to end an affected pregnancy if genetic testing shows the mutation. A third possibility is preimplantation genetic diagnosis. Here, the idea is to use in-vitro fertilization to start pregnancies in the embryology lab. After they incubate for several days, some cells are removed and genetic testing is done.

The couple found this option, while difficult, to be the most acceptable to them. With that in mind, they have embarked on a new journey to have a third child – this time without cataracts.

Stephen Brown, MD, specializes in gynecology, obstetrics, clinical genetics and clinical molecular genetics. His areas of expertise include reproductive genetics and prenatal diagnosis. Dr. Brown is an associate professor in the department of Obstetrics, Gynecology and Reproductive Sciences at the Larner College of Medicine at the University of Vermont.

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