Your Sperm Motility Is Low. Your Genes May Be Why.

MTHFR codes for an enzyme called methylenetetrahydrofolate reductase. Its job is to convert dietary folate into a usable form that your cells use to add methyl groups onto DNA and proteins. This methylation process is essential during sperm development, particularly in the packaging and protection of your DNA as it’s being transferred into sperm cells.

The C677T variant, carried by roughly 40% of people of European ancestry, reduces MTHFR enzyme efficiency by 40 to 70%. That means your cells are struggling to methylate DNA properly during spermatogenesis. Even with adequate folate in your diet, your body can’t convert it fast enough to support normal sperm development.

The practical effect: your sperm have poorly packaged DNA, reduced motility, and higher rates of chromosomal fragmentation. Semen analysis shows the sluggish movement. What it doesn’t show is the DNA damage accumulating inside each cell.

CFTR codes for the cystic fibrosis transmembrane conductance regulator, a protein that controls salt and fluid movement across cell membranes. In your reproductive tract, CFTR is responsible for maintaining proper fluid and electrolyte balance in the vas deferens and seminal fluid, which is essential for sperm transport and motility.

Carrier variants in CFTR (approximately 1 in 25 people of European ancestry) can cause congenital bilateral absence of the vas deferens or partial obstruction. The result is impaired sperm transport and abnormally thick or viscous seminal fluid that reduces sperm motility. Semen analysis often shows normal sperm production but severely diminished movement.

What you experience: normal testosterone, normal semen volume, but sperm that barely move under the microscope. The problem isn’t spermatogenesis; it’s the mechanical environment the sperm are swimming in.

DAZL is part of the azoospermia factor (AZF) gene family on the Y chromosome. It codes for an RNA-binding protein essential for the early stages of spermatogenesis, the process that transforms germ cells into mature sperm. DAZL specifically helps regulate gene expression during this transformation and is critical for sperm cell survival and differentiation.

Deletions or loss-of-function variants in DAZL or the broader AZF region are found in roughly 1 in 2,000 to 3,000 men with infertility. Even partial deletions can severely reduce the number of sperm being produced and drastically reduce their motility. The semen analysis shows severe oligospermia or azoospermia with whatever sperm are present showing minimal movement.

What happens: your body simply isn’t completing the maturation process for most sperm cells. The few that do emerge are often abnormal and immotile. This is one of the more intractable genetic causes of male infertility.

AR codes for the androgen receptor, the protein that allows testosterone and DHT to bind to cells and trigger the genetic programs necessary for sperm production, muscle development, and sexual function. The AR gene contains a variable-length CAG repeat sequence. Longer repeats mean weaker receptor sensitivity; shorter repeats mean stronger sensitivity.

AR CAG repeat length varies across the population, and longer repeats (typically 24 or more) reduce androgen receptor sensitivity significantly. Men with longer CAG repeats have normal testosterone levels but their cells respond poorly to that testosterone. Spermatogenesis slows, sperm motility declines, and erectile function may also be affected despite normal hormone bloodwork.

The practical effect: your doctor checks testosterone and finds it normal, so they tell you the problem isn’t hormonal. But your cells aren’t hearing the testosterone signal properly. Sperm aren’t being produced efficiently, and what sperm do form lack normal motility.

SOD2 codes for superoxide dismutase 2, an enzyme that sits inside the mitochondria and neutralizes dangerous free radicals produced during cellular energy production. Sperm cells are packed with mitochondria in their midpiece, the region that powers their movement. Without adequate antioxidant protection, those mitochondria become damaged and sperm motility collapses.

The common SOD2 Ala16Val variant is carried by a significant portion of the population and subtly reduces enzyme activity. Men with this variant have less antioxidant protection in their sperm mitochondria, making them vulnerable to oxidative stress that specifically impairs motility. Semen analysis often shows normal sperm count and morphology but poor progressive motility.

What you experience: oxidative stress from heat exposure, poor diet, smoking, or even just normal metabolism damages the mitochondria powering sperm movement. Your sperm can’t swim properly, but all the standard tests look relatively normal.

COMT codes for catechol-O-methyltransferase, an enzyme that breaks down dopamine, norepinephrine, and estrogen. In men, COMT is particularly important for maintaining the delicate balance of testosterone and estrogen signaling necessary for spermatogenesis. Slow COMT variants impair catecholamine clearance, leading to elevated estrogen and depleted dopamine.

The Val158Met variant is found in roughly 25% of the population in homozygous form (slow COMT), and these individuals clear dopamine and estrogen much more slowly than others. Slow COMT means estrogen accumulates in your system, which directly suppresses testosterone and spermatogenesis. Your testosterone bloodwork might look normal, but so much of it is being converted to estrogen that sperm production and motility suffer.

The practical effect: you have normal testosterone levels on paper, but elevated estrogen relative to testosterone. Sperm motility declines, libido drops, mood can become more anxious. It feels hormonal, but standard hormone testing misses the real problem because it doesn’t measure the balance.