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 cause infertility and other health problems; it occurs when a child, usually assigned 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 an excess or missing X or Y, are the most common chromosomal conditions, occurring in up to one in 400 births. However, most affected people don’t even know they have it. That’s because these conditions can fly under the radar; they are not life-threatening or necessarily life-limiting and often have no telltale characteristics that raise red flags. Still, 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 discover that their fetus has a much less severe, but much less known, condition. Because so many sex chromosome variations have historically gone undiagnosed, many gynecologists are unfamiliar with these conditions, leaving families to navigate the unexpected news alone. Many end up looking to advocacy organizations, genetic counselors, even Instagram for information as they figure out 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 screen for Down syndrome have over time added a broader spectrum of conditions to their panel, including sex chromosome aneuploidies, the name medical of an atypical number of chromosomes.
“The scariest part is this diagnosis based on a test we didn’t really understand.”
In 2020, the American College of Obstetricians and Gynecologists endorsed NIPS at any age, making the blood test a routine part of pregnancy care. Parents often use these tests to rule out Down syndrome or more serious conditions, only to find, in many cases, something they didn’t even realize their baby was being screened for. “The scariest part is this diagnosis based on a test we didn’t really understand,” says Simon. Adds Katie: “We were assuming that the test would only detect very serious things.”
To add to the complexity, NIPS is not as reliable for sex chromosome aneuploidies as it is for Down syndrome, underscoring the importance of confirming a positive result during pregnancy by amniocentesis or chorionic villus sampling (which examines the placental tissue) or with a blood. show after the baby is born. However, the data suggest that “some women have chosen to terminate their pregnancies solely on the basis of [noninvasive prenatal screening] results, which can abort unaffected fetuses,” according to a 2016 article in Prenatal Diagnosiss.
About 40 percent of men with XXY are diagnosed in their lifetime, usually when they experience fertility problems as adults, says Nicole Tartaglia, a world expert on sex chromosome variations. People with XXY may have learning disabilities and challenges with social interaction, along with 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 live productive and healthy lives.
Meanwhile, only 10% of people with XXX or XYY are aware of their condition. But those numbers are growing as genetic testing becomes more widespread. “Judging by the number of phone calls we get, the proportion of those who go undiagnosed is getting smaller and smaller,” he says.
