Male infertility (genetic causes)

Endocrine and Reproductive Disorders/Infertility

Last updated 3mo ago

A 32-year-old man with primary infertility for 2 years has azoospermia on two semen analyses, normal LH/FSH/testosterone, and normal testicular volume. Karyotype is 46,XY. Y chromosome microdeletion testing reveals an AZFc deletion. Counseling covers the option of testicular sperm extraction with ICSI and the certainty that any resulting sons will inherit the same AZFc deletion and infertility.

Roughly 15% of couples experience infertility, and a male-factor contribution is identified in ~50% of these, about half of the time as the sole cause. The genetic workup is structured by the semen-analysis phenotype (azoospermia vs. severe oligospermia) and is most productive in the non-obstructive category, where chromosomal and Y-microdeletion findings are common. This page covers the major genetic causes; obstructive and acquired causes (varicocele, infection, vasectomy) are outside its scope.

Y Chromosome Microdeletions (AZF region)

Microdeletions in the azoospermia factor (AZF) region of Yq11 are the most common molecular cause of non-obstructive azoospermia / severe oligospermia. Detected by sequence-tagged-site (STS) PCR, not by routine karyotype.

Region	Effect	Sperm retrieval (TESE)
AZFa deletion	Sertoli-cell-only phenotype, no germ cells	Almost never successful
AZFb deletion	Maturation arrest at spermatocyte stage	Almost never successful
AZFc deletion	Variable: severe oligospermia or azoospermia, some spermatogenesis usually present	Often successful
AZFa+b+c (entire AZF)	Sertoli-cell-only	Not successful

Counseling:

Vertical transmission: a son conceived from AZFc-deleted sperm via ICSI will inherit the deletion and the infertility, a near-certain phenotype reproduction in the next generation.
AZFa or AZFb full deletion essentially excludes successful TESE.
AZFc partial (gr/gr) deletions are a milder risk factor with debated penetrance.

Klinefelter Syndrome (47,XXY)

The most common chromosomal cause of male infertility (~3–4% of azoospermic men, ~10–15% of those with non-obstructive azoospermia). Most carry the karyotype undiagnosed until fertility workup. Phenotype: tall stature, gynecomastia, small firm testes, elevated FSH/LH with low-normal testosterone. Karyotype is the diagnostic test. Sperm retrieval is sometimes possible (microTESE in young patients) before progressive testicular failure. See the dedicated Klinefelter syndrome leaf.

Cystic Fibrosis (CFTR) → CBAVD

Congenital bilateral absence of the vas deferens (CBAVD) is the urologic phenotype in ~98% of men with classic cystic fibrosis and ~75% of men with otherwise-asymptomatic CFTR mutations. Presents as obstructive azoospermia with normal testicular function (normal LH/FSH/testosterone, normal sperm production on testicular biopsy). Workup: physical exam (palpable absence of vas), CFTR sequencing including 5T variant in intron 9 (a hypomorphic allele common in CBAVD-only presentations). Partner screening for CFTR before sperm retrieval + ICSI is essential because of the recurrence risk in offspring. See the dedicated Cystic fibrosis leaf.

Kallmann Syndrome / Congenital Hypogonadotropic Hypogonadism

GnRH-deficient hypogonadotropic hypogonadism, often (but not always) with anosmia (Kallmann form). Genetics is heterogeneous: ANOS1 (X-linked, with anosmia + mirror movements + renal agenesis), FGFR1, PROK2/PROKR2, CHD7 (overlap with CHARGE), and many others. Phenotype: absent or arrested puberty, low testosterone, low/inappropriately-normal LH/FSH, small testes. Fertility is restorable with pulsatile GnRH or gonadotropin therapy in most cases, distinguishing this category from primary testicular failures. See the dedicated Kallmann syndrome leaf.

Androgen Insensitivity Syndrome (AIS)

X-linked AR mutation. Complete AIS (CAIS) presents as a phenotypic female with primary amenorrhea, intra-abdominal testes, and 46,XY karyotype. Partial AIS (PAIS) spans a phenotypic spectrum from undervirilized male to ambiguous genitalia; mild forms can present with adult-onset gynecomastia and infertility (oligospermia/azoospermia). Workup includes karyotype, AR sequencing, and androgen sensitivity testing. See the dedicated Androgen insensitivity syndrome leaf.

Balanced Chromosomal Rearrangements (carriers)

Reciprocal translocations and Robertsonian translocations cause meiotic disruption that impairs spermatogenesis (the carrier produces a high fraction of unbalanced gametes; many fail to mature). Found in ~5% of azoospermic men and ~1–3% of severely oligospermic men. Karyotype is the test; microarray will miss balanced rearrangements. Counseling addresses both the partner's miscarriage risk and the live-born unbalanced offspring risk; PGT-SR (preimplantation genetic testing for structural rearrangement) is increasingly offered. See Structural Rearrangements & NAHR for the segregation math.

Other Genetic Contributors

47,XYY: typically fertile but mildly increased rate of oligospermia.
CAG repeat polymorphism in AR: long repeats associated with reduced androgen sensitivity and modest sperm-count reduction.
Globozoospermia (round-headed sperm; DPY19L2 mutations): failure of acrosome formation.
Multiple morphological abnormalities of the flagella (MMAF) and motile-cilia dysfunction (DNAH1, CFAP43/44): sperm flagellum is a cilium; some primary-ciliary-dyskinesia genes cause infertility.
Kartagener (PCD): see Cilia & Ciliopathies; affected men have immotile sperm flagella.

Non-obstructive azoospermia / severe oligospermia with genetic etiology: typically normal physical exam, sometimes elevated FSH (Sertoli-cell-only or maturation arrest).
Obstructive azoospermia with normal spermatogenesis: palpable absent vas + CFTR finding.
Hypogonadotropic picture (low T, low/normal LH/FSH) → think Kallmann / hypothalamic-pituitary axis.
Hypergonadotropic picture (low T, high FSH/LH) → think Klinefelter or primary testicular failure.

The structured workup, anchored by semen analysis:

Two semen analyses confirming azoospermia or severe oligospermia.
Hormonal panel: FSH, LH, total testosterone, prolactin, estradiol.
Karyotype: first-line for any man with non-obstructive azoospermia or oligospermia <5 M/mL. Catches Klinefelter and balanced translocations.
Y chromosome microdeletion testing (STS-PCR): for non-obstructive azoospermia or severe oligospermia. Routine karyotype does NOT detect these; specific microdeletion panel is needed.
CFTR testing: for obstructive azoospermia with palpable absence of vas. Include 5T variant analysis.
Targeted testing based on phenotype: Kallmann panel (ANOS1, FGFR1, etc.) for hypogonadotropic; AR sequencing for undervirilization features.

The American Urological Association / American Society for Reproductive Medicine 2024 guideline endorses karyotype + Y microdeletion testing as the standard initial genetic workup for non-obstructive azoospermia and severe oligospermia.

Assisted reproduction with ICSI (intracytoplasmic sperm injection) is the dominant intervention. Sperm sources: ejaculated (if any), epididymal aspiration (CBAVD), or testicular extraction (microTESE for non-obstructive cases).
Hormonal therapy for Kallmann / hypogonadotropic hypogonadism: pulsatile GnRH or gonadotropin (hCG ± FSH) often restores fertility.
Klinefelter: earlier microTESE may improve sperm-retrieval success before progressive testicular sclerosis.
CFTR carriers: partner screening before ICSI; PGT-M if both partners carry pathogenic variants.
Counseling must address vertical transmission, especially for AZFc microdeletions (sons inherit) and X-linked Kallmann (daughters carry).

"AZF a, b, c → no sperm, no sperm, sometimes sperm": AZFa and AZFb deletions effectively rule out TESE success; AZFc allows it.

"Klinefelter is the karyotype find; AZF needs its own test": chromosomal vs. submicroscopic; the genetic workup needs both karyotype AND Y-microdeletion panel.

"CBAVD = CFTR until proven otherwise": palpable absent vas with normal testicular volume → CFTR sequencing including the 5T variant.

"Kallmann is the curable cause": hypogonadotropic; restorable with hormonal therapy unlike primary testicular failures.