What to expect when expecting an extra X or Y chromosome
Katie and her husband, Simon, had never heard of XXY, and their obstetrician wasn’t much help either. Also known as Klinefelter syndrome, XXY is a genetic condition that can lead to infertility and other health issues. it occurs when a child, usually designated male at birth, is born with an extra X chromosome in addition to the usual X and Y.
Sex chromosome variations, in which people have a surplus or a missing X or Y, are the most common chromosomal conditions, occurring in one in every 400 births. Yet the majority of people affected don’t even know they have them. are reached. This is because these conditions can fly under the radar; they are not life threatening or necessarily life limiting and often do not have telltale characteristics that trigger red flags. Yet the diagnosis can cause distress.
As more expectant parents opt for non-invasive prenatal testing in hopes of ruling out serious conditions, many are surprised to find their fetus has a much less serious condition instead. , but much less known. Because so many sex chromosome variations have never been diagnosed, many obstetricians are unfamiliar with these conditions, leaving families to deal with unexpected news on their own. Many end up seeking information from advocacy organizations, genetic counselors, and even Instagram as they determine their next steps..
The information landscape has changed dramatically since the advent of non-invasive prenatal screening (NIPS) a decade ago. The increasingly popular first-trimester blood tests that debuted in 2011 to detect Down syndrome have, over time, added a wider range of conditions to their panel, including sex chromosome aneuploidies – the medical name for an atypical number of chromosomes.
“The scariest part here is this diagnosis based on a test that we didn’t really understand.”
In 2020, the American College of Obstetricians and Gynecologists endorsed NIPS at any age, making blood testing a routine part of pregnancy care. Parents typically use these tests to rule out Down syndrome or more serious conditions, only to in many cases discover something they didn’t even know their baby was being screened for. “The scariest part here is this diagnosis based on a test that we didn’t really understand,” says Simon. Katie adds: “We assumed the test would only detect very serious things.”
To add to the complexity, the NIPS is not as reliable for sex chromosome aneuploidies as it is for Down syndrome, highlighting the importance of confirming a positive screening result during pregnancy via amniocentesis or blood sample. chorionic villi (which examines placental tissue), or with a blood test. sample after the baby is born. Yet the data suggests that “some women chose to terminate their pregnancies solely on the basis of [noninvasive prenatal screening] results, potentially aborting unaffected fetuses,” according to a 2016 article in Prenatal Diagnosis.
About 40% of men with XXY are diagnosed during their lifetime, usually when they experience fertility problems in adulthood, says Nicole Tartaglia, a world expert on sex chromosome variations. People with XXY may have learning difficulties and problems with social interaction, as well as physical traits such as small testicles, a less muscular body, and less facial and body hair. But most people with Klinefelter syndrome grow up to lead productive, healthy lives.
Meanwhile, only 10% of people with XXX or XYY are aware of their condition. But these numbers are increasing as genetic testing becomes more widespread. “Judging by the number of phone calls we receive, the proportion of those who are undiagnosed is decreasing,” she says.