There are a lot of things you might want to inherit from your father—intelligence, musical talent, money—but infertility probably isn't one of them.
If you've been struggling to conceive, you may find yourself wondering if the problem came from your parents. Sure, inherited infertility may sound a bit contradictory, but if your parents can pass down sickle cell anemia, muscular dystrophy and hemophilia, it's not too crazy to think they might pass down infertility, as well…right?
If you haven't identified the source of your fertility challenges, however, don't rush to blame Mom and Dad just yet. While infertility can be inherited, in the vast majority of cases, it's not.
Possible? Yes. Likely? No.
Dr. Paul Turek, a leading expert in male reproductive health and founder/owner of the Turek Clinic in Los Angeles and San Francisco, estimated that only about 5 percent of the infertility cases he sees are due primarily to inherited diseases, traits or conditions.
"Most of infertility genetics is de novo, not Mendelian," Turek said, meaning the genetic mutation causing a man to struggle with infertility will often appear for the first time in him, not in his parents or other relatives. ("De novo," meaning "from the beginning"; "Mendelian," referring to Gregor Mendel's theory of biological inheritance and dominant and recessive genes.)
Still, a number of different conditions associated with infertility can be passed from one generation to the next. Some of the most easily inherited ones include: chromosomal abnormalities such as translocations, occurring when a chromosome breaks and reattaches in part to a different chromosome; sperm aneuploidy, an abnormal number of chromosomes in sperm cells; and inversions, a chromosome segment breaks off, reverses from end to end and reattaches.
"These are typically inherited because they're associated with low, but not no, sperm count," Turek explained. "Fertility isn't correlated with sperm count unless it's zero, so you can be perfectly fertile with [these conditions] and still pass them on."
Inherited infertility, courtesy of Mom or Dad
You might not think your mom's genes could have anything to do with your sperm count, but believe it or not, it's possible. A few different causes of infertility are linked specifically to the X chromosome men inherit from their mothers, Turek said. In fact, researchers recently discovered that mutations of a gene called TEX11 can lead to azoospermia, or semen without sperm.
"A woman can harbor a TEX11 mutation that won't affect her, but she'll give it to her son. Since he can only get an X chromosome from her, and that gene is bad, it can cause infertility," Turek said. "It's not common, but there are lots of little ones like that."
Other known or suspected X-linked mutations that affect fertility include AR, RHOX, ANOS1, USP26, and TAF7L.
But infertility can also be linked to the Y chromosome you get from your dad. A disorder called Y chromosome microdeletion, where certain gene regions on the Y chromosome are missing, results in no sperm, fewer sperm or poor-quality sperm. This is almost always a de novo mutation, although it is technically possible for it to be inherited. Men with Y chromosome microdeletion who use assisted reproductive technology (ART) to biologically father children will pass this disorder down to any sons they might have.
"Y chromosome deletions are almost always new to that generation," Turek said. "But if a man has a Y chromosome deletion and his female partner's really fertile, they can have a baby. [The child] would have a lower sperm count, though."
Birth defects may be to blame
Other inheritable forms of infertility are related to congenital defects, Turek said. Some mutations of the CFTR genes can cause cystic fibrosis, a life-threatening lung disorder and/or missing vas deferens at birth in males. CFTR stands for cystic fibrosis transmembrane conductance regulator. If your memory of sex ed is hazy, vas deferens are the tubes that carry sperm from the epididymis to the urethra in preparation for ejaculation. Without them, a man would have to rely on assisted reproductive technology to have biological children.
Congenital absence of the vas deferens is an autosomal recessive condition, meaning males received one mutated CFTR gene from each of their parents. If a man with this gene mutation uses ART to conceive, the child will have an increased risk of CFTR mutations and associated conditions, as well.
Another defect that can lead to fertility problems is undescended testicles. While not "classically genetic," Turek said, genetics is likely one factor that influences the absence or presence of the condition.
"Undescended testicles are one of the most common birth defects in America," Turek said, with about 30 percent of premature and 3 percent of full-term male babies born with one or two undescended testicles.
"It's pretty correctable, but [men] can have sustained problems afterwards," Turek explained. "If you have two undescended testicles at birth and you get it fixed, your chance of having any sperm in your ejaculate later in life is probably 25 percent."
When in doubt, call your doc
If you haven't yet identified the source of your infertility and suspect it might be genetic, you'll probably want to see a fertility specialist and/or genetic counselor.
No couple trying to conceive wants to hear a diagnosis of genetic infertility, of course, but it's far from the end of the world. After all, once you know the root cause of your infertility, you're better prepared to overcome it.
"Knowing that [infertility] is genetic still tells you a lot. Even if it means other treatments won't help, you at least know that you should turn to technology if you want a kid," Turek said. "By avoiding unnecessary treatments, it streamlines the care, and you save time, energy and money."