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PubMed This is a summary of 18 peer-reviewed journal articles Updated
Urology · Y-Chromosome Microdeletion

Decoding Your Subtype: AZFa, AZFb, and AZFc

At a Glance

Y-chromosome microdeletions are divided into AZFa, AZFb, and AZFc subtypes. Complete AZFa and AZFb deletions halt sperm production, making biological fatherhood extremely rare. AZFc is the most common subtype and offers a 50-70% chance of successfully retrieving sperm using micro-TESE surgery.

A diagnosis of Y-chromosome microdeletion (YCMD) is not a single, uniform condition. Instead, it is divided into three primary subtypes—AZFa, AZFb, and AZFc—based on which “missing pieces” of DNA are absent from your Y chromosome [1][2]. Understanding your specific subtype is the most important factor in determining the likelihood of finding viable sperm for biological fatherhood [3][4].

The Three Main Subtypes

The impact of a deletion depends almost entirely on which region is affected.

Subtype Impact on Sperm Production Sperm Retrieval Success (micro-TESE)
AZFa Sertoli Cell-Only Syndrome (SCOS): No germ cells are present to create sperm [5]. Extremely rare to impossible [6].
AZFb Maturation Arrest: Sperm production starts but stops before completion [2]. Extremely rare to impossible [6].
AZFc Variable: Range from low sperm count (oligozoospermia) to zero sperm (azoospermia) [1]. High: Approximately 50-70% success rate [7][8].

AZFa and Sertoli Cell-Only Syndrome

A complete AZFa deletion usually leads to a condition called Sertoli cell-only syndrome (SCOS) [2]. Within the testicles, there are specialized cells called Sertoli cells that act as “nurses” to support developing sperm [9]. In SCOS, the “nurses” are present, but the “patients” (the germ cells that become sperm) are missing entirely [9][10]. Because the fundamental building blocks of sperm are absent, surgical attempts to find sperm in men with complete AZFa deletions are almost always unsuccessful [5][11].

AZFb and Maturation Arrest

Complete AZFb deletions typically result in maturation arrest [2]. In this case, the germ cells are present, and they begin the process of becoming sperm, but they cannot finish it [2]. They “stall” at an early stage of development, which means that even with surgery, mature, viable sperm are rarely found [6].

AZFc: The “Hopeful” Subtype

The AZFc deletion is the most common form of YCMD and offers the best prognosis for biological children [1][7]. Many men with AZFc deletions still have small “pockets” of active sperm production within their testicles [12]. This allows for two possibilities:

  • Cryptozoospermia: Occasionally, small amounts of sperm may be found in the semen if multiple samples are analyzed [13].
  • Micro-TESE: A surgeon uses a high-powered microscope to find those active “pockets” of sperm production directly in the testicular tissue [7][4].

“Complete” vs. “Partial” Deletions

You may hear your doctor mention whether a deletion is complete or partial.

  • Complete Deletion: The entire AZF region (a, b, or c) is missing. The outcomes described in the table above apply to complete deletions [2].
  • Partial Deletion (e.g., “gr/gr”): Only a portion of a region is missing [14]. Partial deletions, especially in the AZFc region (like the gr/gr deletion), have more variable outcomes [14][15]. Some men with partial deletions may have near-normal sperm counts, while others may experience significant infertility [14][16]. It is also important to note that partial deletions can sometimes “expand” into complete deletions when passed to a son [17][18].

Once you know your subtype, you can determine your Treatment Strategy.

Common questions in this guide

What is the difference between AZFa, AZFb, and AZFc deletions?
These are specific regions of the Y chromosome that contain genes needed for sperm production. A complete deletion in the AZFa or AZFb region typically means sperm cannot be produced. An AZFc deletion is less severe and often allows doctors to retrieve viable sperm surgically.
Can I still have biological children with an AZFa or AZFb deletion?
Biological fatherhood is extremely rare to impossible with a complete AZFa or AZFb deletion. These deletions cause conditions where mature sperm are completely absent or stop developing early, meaning sperm cannot be found even with specialized surgery.
What are my chances of finding sperm with an AZFc deletion?
Men with an AZFc deletion have the best prognosis for biological fatherhood. Using a specialized surgery called micro-TESE, doctors can successfully find and retrieve viable sperm directly from the testicles in approximately 50% to 70% of cases.
What does a partial Y-chromosome deletion like gr/gr mean?
A partial deletion means only a piece of the genetic region is missing, rather than the whole section. The outcomes for partial deletions vary widely, ranging from near-normal sperm counts to severe infertility.
Will my son inherit my Y-chromosome microdeletion?
Yes, because the deletion is on the Y chromosome, any biological son conceived using your sperm will inherit the microdeletion. Additionally, partial deletions can sometimes expand into more severe, complete deletions in the next generation.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Does my genetic test confirm a 'complete' or 'partial' deletion of the AZF region?
  2. 2.Given my specific subtype (AZFa, AZFb, or AZFc), what is the statistical likelihood of retrieving sperm during a micro-TESE?
  3. 3.If I have an AZFc deletion, what are the chances of finding sperm in my semen sample over multiple tests (cryptozoospermia)?
  4. 4.If sperm is found and we use ICSI, what are the specific risks of vertical transmission to my son, and could the deletion become more severe in him?
  5. 5.Does my subtype diagnosis suggest that I should also be monitored for any other health issues, such as changes in testosterone levels?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (18)
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    Association of Y Chromosome Microdeletions with Reproductive Profiles in 2010 Infertile Male Patients in China.

    Chen G, Huang P, Li H, et al.

    The application of clinical genetics 2025; (18()):275-282 doi:10.2147/TACG.S560740.

    PMID: 41458066
  2. 2

    Histology and sperm retrieval among men with Y chromosome microdeletions.

    Yuen W, Golin AP, Flannigan R, Schlegel PN

    Translational andrology and urology 2021; (10(3)):1442-1456 doi:10.21037/tau.2020.03.35.

    PMID: 33850779
  3. 3

    Successful microdissection testicular sperm extraction for men with non-obstructive azoospermia.

    Klami R, Mankonen H, Perheentupa A

    Reproductive biology 2018; (18(2)):137-142 doi:10.1016/j.repbio.2018.03.003.

    PMID: 29602610
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    Prediction Models for Successful Sperm Retrieval in Patients with Non-Obstructive Azoospermia Undergoing Microdissection Testicular Sperm Extraction: Is There Any Room for Further Studies?

    Caroppo E, Colpi GM

    Journal of clinical medicine 2021; (10(23)) doi:10.3390/jcm10235538.

    PMID: 34884245
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    Unveiling Leydig cell heterogeneity and its role in male infertility: A single-cell transcriptomic study of human testicular tissue.

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    Reproductive biology 2025; (25(1)):100972 doi:10.1016/j.repbio.2024.100972.

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    Whole transcriptome analysis to identify non-coding RNA regulators and hub genes in sperm of non-obstructive azoospermia by microarray, single-cell RNA sequencing, weighted gene co-expression network analysis, and mRNA-miRNA-lncRNA interaction analysis.

    Karoii DH, Azizi H, Skutella T

    BMC genomics 2024; (25(1)):583 doi:10.1186/s12864-024-10506-9.

    PMID: 38858625
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    [Analysis of clinical outcome of synchronous micro-dissection testicular sperm extraction and intracytoplasmic sperm injection in male infertility with Y chromosome azoospermia factor c region deletion].

    Mao JM, Zhao LM, Liu DF, et al.

    Beijing da xue xue bao. Yi xue ban = Journal of Peking University. Health sciences 2022; (54(4)):652-657.

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    Micro-TESE strategy in patients with NOA caused by AZFc deletion: synchronous or asynchronous?

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    Zygote (Cambridge, England) 2023; (31(1)):25-30 doi:10.1017/S0967199422000466.

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    Sertoli cell-only syndrome (Del Castillo syndrome): Past, present and future.

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    Sertoli Cell-Only Syndrome: Behind the Genetic Scenes.

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    Investigation of genotype-phenotype correlation in patients with AZF microdeletion in a single-reference centre.

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    Y chromosome microdeletions in Chinese men with infertility: prevalence, phenotypes, and intracytoplasmic sperm injection outcomes.

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    Impact of AZFc deletion subtypes on sperm retrieval rates via micro-TESE and ICSI outcomes in non-obstructive azoospermia patients.

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    Multiplex PCR based screening for micro/partial deletions in the AZF region of Y-chromosome in severe oligozoospermic and azoospermic infertile men in Iran.

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This page explains YCMD subtypes and their impact on sperm retrieval for educational purposes only. Always consult a urologist or fertility specialist for personal medical advice and family planning.

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