Azoospermia - Genetic causes

Chromosomal abnormalities (non-AZF)

• Klinefelter syndrome (47,XXY)
  Most common cause of non-obstructive azoospermia.
  Mosaic forms (46,XY/47,XXY) may have focal spermatogenesis.
• Structural rearrangements
  Balanced translocations, inversions, ring chromosomes.
  Often severe spermatogenic arrest.

Monogenic causes of non-obstructive azoospermia

These affect meiosis, germ cell development, or Sertoli cell function.

Obstructive azoospermia with intact spermatogenesis

Y-microdeletion testing - normal.

• CFTR mutations
  • Congenital bilateral absence of vas deferens (CBAVD)
  • Testes normal size, normal FSH, low semen volume, acidic pH
• ADGRG2 mutations (X-linked)
  • CFTR-negative CBAVD

Disorders of sex development spectrum (mild)

• May present only with infertility.
• Partial gonadal dysgenesis
• NR5A1, WT1 variants

Mitochondrial and spermiogenesis-specific genes

• Severe oligozoospermia or azoospermic.
• DNAH genes
• SPATA genes
• TEX14

Step 1: Confirm true azoospermia

• Two semen analyses with centrifugation
• Exclude cryptozoospermia

Step 2: Hormonal profile

• FSH, LH, testosterone, prolactin
• High FSH + small testes → non-obstructive pattern
• Normal FSH + normal testes → suspect obstruction

Step 3: Karyotype (essential)

• Detects 47,XXY and structural abnormalities
• Should be done in all azoospermic men

Step 4: Targeted gene testing

If obstructive pattern

• CFTR mutation analysis (including 5T variant)
• ADGRG2 if CFTR negative and CBAVD suspected

If non-obstructive pattern

• Gene panel or WES focusing on spermatogenesis genes (TEX11, NR5A1, DMRT1, meiosis genes)

Step 5: Imaging

• Scrotal ultrasound: testicular volume, microlithiasis
• TRUS if ejaculatory duct obstruction suspected

Step 6: Testicular biopsy / micro-TESE

• Diagnostic and therapeutic
• Histology guides prognosis
• Sertoli cell-only
• Maturation arrest
• Hypospermatogenesis

Y-chromosome microdeletion

Submicroscopic deletions on Yq11, involving regions essential for spermatogenesis. They are not visible on karyotype and require PCR or molecular testing.

These deletions affect the AZF regions (Azoospermia Factor):

• AZFa
• AZFb
• AZFc
• Sometimes combined (AZFbc, AZFabc)

They are among the commonest known genetic causes of non-obstructive azoospermia (NOA).

Epidemiology

• Present in:
• ~10–15% of men with non-obstructive azoospermia
• ~5–7% with severe oligozoospermia
• Rare in fertile men
• Risk increases as sperm count decreases

The type of AZF deletion alone determines prognosis and management.

Hormones, ultrasound, and age cannot override this.

AZF Types, Meaning, and Counseling

AZF region	Key genes (examples)	Typical testicular histology	Chance of sperm retrieval	Management advice	Counseling message
AZFa	USP9Y, DDX3Y	Sertoli cell–only	~0%	❌ Do not attempt TESE	“This deletion prevents sperm cells from forming. Surgical retrieval is not helpful.”
AZFb	RBMY1, EIF1AY	Complete maturation arrest	<5%	❌ TESE generally futile	“Sperm development stops early. Finding usable sperm is extremely unlikely.”
AZFc	DAZ, CDY1, BPY2	Variable: focal spermatogenesis possible	40–70%	✅ micro-TESE recommended	“Some sperm production may be present in small areas. Surgery may succeed.”
AZFbc / AZFabc	Combined loss	Severe germ cell failure	~0%	❌ Do not attempt TESE	“This is equivalent to AZFb or worse in outcome.”

Typical clinical pattern

• Non-obstructive azoospermia
• FSH often elevated
• Testes may be small or normal
• No effect on sexual function or general health

What AZF deletions do NOT cause

• No birth defects
• No intellectual disability
• No hormonal syndromes
• No increased cancer risk

This is isolated testicular failure, not a systemic disorder.

Inheritance and offspring risk

• All male offspring will inherit the same AZF deletion
• Sons will likely face infertility
• Female offspring are unaffected
• PGT-A does not prevent transmission
• This is a fertility issue, not a childhood disease

Common misunderstandings to clarify

• AZFc ≠ hopeless
• Yq12 deletion ≠ AZF deletion
• Normal testosterone ≠ normal sperm production
• TESE should not be attempted in AZFa or AZFb

Practical counseling line

“The Y-chromosome finding explains why sperm are absent. The exact region involved tells us whether surgery can help. In your case, our plan is based on the AZF type, not guesswork.”

Bottom line

• Always identify the AZF subtype
• AZFa / AZFb → no surgery
• AZFc → micro-TESE + ICSI possible
• Genetic counseling is essential before treatment