Spermatogenic Failure 33

Mendelian MONDO:0029147 Pathograph 16 Show in embeddings browser Spermatogenic Failure Genetic Disease

Spermatogenic failure 33 (SPGF33) is autosomal recessive male infertility caused by biallelic loss-of-function variants in CFAP251 (formerly WDR66). CFAP251 is a WD-repeat subunit of the calmodulin- and spoke-associated complex (CSC), which with CFAP61 and CFAP91 builds the base of radial spoke 3 (RS3) on the peripheral microtubule doublets of the axoneme. In the absence of CFAP251 the CSC and RS3 fail to assemble in sperm, the developing flagellum is disorganized, and men present with asthenoteratozoospermia with multiple morphological abnormalities of the sperm flagella (MMAF): absent, short, coiled, bent and irregular-caliber flagella with low or absent motility. Electron microscopy shows loss of the central pair and radial spokes, disorganized doublets, outer dense fibers and fibrous sheath, and a defective mitochondrial sheath. A recurrent C-terminal deletion of exons 20-21 is a founder allele in North Africa and explains about 15% of MMAF in Tunisian men. Most patients have no respiratory symptoms, but one 2026 report described a cough and chest CT changes in one patient and inner dynein arm loss in tracheal cilia of knockout mice. Intracytoplasmic sperm injection (ICSI) has produced pregnancies and live births.

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Inheritance

1
Autosomal recessive HP:0000007
Disease requires biallelic CFAP251 variants: homozygous variants in consanguineous and founder-allele families, and compound heterozygous variants. One proband with a homozygous splice variant inherited both copies from his mother through maternal uniparental disomy.
Autosomal recessive inheritance
Show evidence (2 references)
PMID:30122541 SUPPORT Human clinical
"In three men, we found bi-allelic loss-of-function mutations in WDR66, encoding cilia- and flagella-associated protein 251 (CFAP251)"
Biallelic loss-of-function variants in affected men.
PMID:35087568 SUPPORT Human clinical
"Interestingly, the patient's mother was a heterozygous carrier for the mutation, but his father was not, and finally, the inheritance pattern was proven to be maternal uniparental disomy."
Homozygosity arising through maternal uniparental disomy, a recessive mechanism with a different recurrence risk.
◈

Mechanistic Hypotheses

2
CFAP251 loss causes isolated male infertility rather than primary ciliary dyskinesia
cfap251_sperm_restricted CANONICAL
Evidence balance 2 support 2 refute
CFAP251 is expressed in both testis and airway, but almost all reported patients have isolated infertility, and a health questionnaire for PCD manifestations was negative in the founder-deletion cohort. In 2026 one patient with a homozygous splice variant was reported with tinnitus, a seasonal cough and chest CT changes (increased lung markings and a pulmonary bulla), and Cfap251 knockout mice had frequent loss of inner dynein arms in tracheal cilia. The human evidence for a respiratory phenotype is a single patient without ciliary biopsy, beat analysis or nasal nitric oxide, so the PCD-like phenotype is unconfirmed, and it is not recorded as a disease phenotype here.
Show evidence (4 references)
PMID:30122540 SUPPORT Human clinical
"All subjects had an isolated MMAF phenotype and no mention of any other PCD symptoms."
No PCD manifestations in a cohort that included seven homozygous founder-deletion carriers.
PMID:41943837 REFUTE Human clinical
"Notably, one patient carrying biallelic CFAP251 mutations showed PCD-like symptoms, including tinnitus, seasonal cough, and radiological findings of coarsened lung markings and a solitary pulmonary bulla associated with chronic bronchitic inflammation."
A single patient with respiratory symptoms and CT changes, without ciliary investigation.
PMID:41943837 REFUTE Model organism
"Although the loss of CFAP251 in the respiratory cilia of Cfap251-/- mice did not result in overt defects in ciliary length or density, TEM revealed a frequent absence of inner dynein arms within the axoneme."
Knockout mice have an ultrastructural defect in tracheal cilia.
+ 1 more reference
CFAP251 recruits TUBB4B and SLC25A4 to the developing sperm flagellum
cfap251_tubb4b_slc25a4_recruitment EMERGING
Evidence balance 3 support
A single 2026 study found that CFAP251 binds the beta-tubulin TUBB4B and the mitochondrial ADP/ATP carrier SLC25A4 (testis pull-down with mass spectrometry, co-immunoprecipitation in vitro, and structural modelling), that both proteins are reduced in Cfap251 knockout testis and along knockout sperm flagella, and that their flagellar immunofluorescence is reduced in sperm of two men with homozygous CFAP251 splice variants. The authors propose that CFAP251 is a scaffold needed to incorporate both proteins into the flagellum, which would add a tubulin-supply and an energy-transport component to the radial spoke 3 defect. It has not been replicated, and no experiment separates the contribution of these two proteins from that of radial spoke loss.
Pathograph links
Loss of CFAP251 -> Reduced TUBB4B and SLC25A4 Recruitment to the Sperm Flagellum DIRECT CFAP251 binds beta-tubulin TUBB4B and the mitochondrial ADP/ATP carrier SLC25A4; without it both proteins are reduced in testis and along the sperm flagellum.
Reduced TUBB4B and SLC25A4 Recruitment to the Sperm Flagellum -> Sperm Axonemal Disorganization INDIRECT UNKNOWN INTERMEDIATES Proposed to contribute to flagellar disorganization and, through SLC25A4, to the midpiece energy-supply defect. Which part of the axonemal and mitochondrial sheath phenotype depends on these two proteins, rather than on radial spoke 3 loss, has not been tested.
Show evidence (3 references)
PMID:41943837 SUPPORT In vitro / ex vivo
"Co-IP assays demonstrated strong interactions between TUBB4B, SLC25A4, and CFAP251 in vitro (Figure 6F and G)"
Physical interaction of CFAP251 with both partners.
PMID:41943837 SUPPORT Model organism
"The levels of TUBB4B and SLC25A4 were reduced in Cfap251-/- testes, whereas CABYR and AKAP3 levels were unaffected (Figure 6H and I)."
Loss of both partners in knockout testis.
PMID:41943837 SUPPORT Human clinical
"The results revealed a significant downregulation of the colocalization signals for both TUBB4B and SLC25A4 in the sperm flagellum (Supplementary Figure 9A and B)."
The same reduction in patient sperm.
⚙

Pathophysiology

5
Loss of CFAP251
Frameshift, nonsense, splice-site and large C-terminal deletion alleles abolish or sharply reduce CFAP251 in sperm. CFAP251 is normally present along the whole flagellum, with a sperm-specific isoform produced during maturation. It is a structural WD-repeat scaffold of the calmodulin- and spoke-associated complex at the base of radial spoke 3.
CFAP251 recruits TUBB4B and SLC25A4 to the developing sperm flagellum
CFAP251 hgnc:28506 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves CFAP251 (hgnc:28506). hgnc:28506 is a gene from the HUGO Gene Nomenclature Committee.
structural constituent of the axonemal cytoskeleton GO:0005200 ↓ DECREASED Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves decreased structural constituent of the axonemal cytoskeleton, annotated with structural constituent of cytoskeleton (GO:0005200). GO:0005200 is a molecular function from the Gene Ontology.
Radial spoke base 3 GO:0120342 Gene Ontology (GO) Relation: this pathophysiological event involves this cellular component This pathophysiological event involves Radial spoke base 3 (GO:0120342). GO:0120342 is a cellular component from the Gene Ontology.
Downstream
Loss of the Calmodulin- and Spoke-Associated Complex from the Sperm Axoneme CFAP251 is itself a CSC subunit; without it the arch-like density at the base of RS3 is missing and the spoke is incomplete.
Reduced TUBB4B and SLC25A4 Recruitment to the Sperm Flagellum CFAP251 binds beta-tubulin TUBB4B and the mitochondrial ADP/ATP carrier SLC25A4; without it both proteins are reduced in testis and along the sperm flagellum. CFAP251 recruits TUBB4B and SLC25A4 to the developing sperm flagellum
Show evidence (3 references)
PMID:30122541 SUPPORT Human clinical
"We show that CFAP251 is normally located along the flagellum but is absent in men carrying WDR66 mutations and reveal a spermatozoa-specific isoform probably generated during spermatozoon maturation."
Patient sperm lack CFAP251.
PMID:41943837 SUPPORT Human clinical
"Furthermore, CFAP251 was detected along the length of the flagella in spermatozoa from the control individuals but was absent in those of F1 IV-1 and F2 II-1, confirming a complete loss of CFAP251 (Figure 6F)."
Homozygous splice alleles remove CFAP251 from sperm.
PMID:30122540 SUPPORT Human clinical
"It was found in seven apparently unrelated North African individuals and removed exons 20 and 21 out of 22 of WDR66."
The founder deletion removes the C-terminal region of the protein.
Reduced TUBB4B and SLC25A4 Recruitment to the Sperm Flagellum
Co-immunoprecipitation and mass spectrometry of mouse testis identified the beta-tubulin TUBB4B and the mitochondrial ADP/ATP carrier SLC25A4 as CFAP251 partners, and both co-immunoprecipitate with CFAP251 in vitro. In elongating spermatids both colocalize with tubulin, and in mature sperm TUBB4B is enriched in the principal piece and SLC25A4 in the midpiece. Both proteins are reduced in Cfap251 knockout testis and along knockout sperm flagella, and their flagellar signal is reduced in sperm of men with CFAP251 splice variants. The authors propose that CFAP251 is a scaffold for the stable incorporation of TUBB4B and SLC25A4 into the flagellum; this rests on one study.
CFAP251 recruits TUBB4B and SLC25A4 to the developing sperm flagellum
Sperm CL:0000019 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves Sperm (CL:0000019). CL:0000019 is a cell type from the Cell Ontology.
TUBB4B hgnc:20771 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves TUBB4B (hgnc:20771). hgnc:20771 is a gene from the HUGO Gene Nomenclature Committee. SLC25A4 hgnc:10990 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves SLC25A4 (hgnc:10990). hgnc:10990 is a gene from the HUGO Gene Nomenclature Committee.
TUBB4B structural constituent of the flagellar cytoskeleton GO:0005200 ↓ DECREASED Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves decreased TUBB4B structural constituent of the flagellar cytoskeleton, annotated with structural constituent of cytoskeleton (GO:0005200). GO:0005200 is a molecular function from the Gene Ontology. SLC25A4 ADP/ATP exchange GO:0005471 ↓ DECREASED Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves decreased SLC25A4 ADP/ATP exchange, annotated with ATP:ADP antiporter activity (GO:0005471). GO:0005471 is a molecular function from the Gene Ontology.
Sperm flagellum GO:0036126 Gene Ontology (GO) Relation: this pathophysiological event involves this cellular component This pathophysiological event involves Sperm flagellum (GO:0036126). GO:0036126 is a cellular component from the Gene Ontology.
Downstream
Sperm Axonemal Disorganization Proposed to contribute to flagellar disorganization and, through SLC25A4, to the midpiece energy-supply defect. Which part of the axonemal and mitochondrial sheath phenotype depends on these two proteins, rather than on radial spoke 3 loss, has not been tested. CFAP251 recruits TUBB4B and SLC25A4 to the developing sperm flagellum
Show evidence (2 references)
PMID:41943837 SUPPORT Model organism
"In mature spermatozoa, TUBB4B and SLC25A4 labeling was observed along the entire flagellum, with TUBB4B signal enriched in the principal piece and SLC25A4 concentrated in the midpiece (Figures 5J and L)."
Flagellar localization of both partners in mouse sperm.
PMID:41943837 SUPPORT Human clinical
"The results revealed a significant downregulation of the colocalization signals for both TUBB4B and SLC25A4 in the sperm flagellum (Supplementary Figure 9A and B)."
Reduced flagellar TUBB4B and SLC25A4 in patient sperm.
Loss of the Calmodulin- and Spoke-Associated Complex from the Sperm Axoneme
The CSC (CFAP61, CFAP91 and CFAP251 with calmodulin) sits at the base of radial spoke 3 and links it to the doublet microtubules. Loss of any one subunit destabilizes the others: CFAP251 is lost from sperm of men with CFAP61 variants and from Cfap91 knockout sperm, and in Cfap251 knockout mice the radial spoke proteins RSPH1 and RSPH3 are reduced along the flagellum. Radial spoke 3 therefore fails to assemble.
Radial spoke assembly GO:0062177 ↓ DECREASED Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased Radial spoke assembly (GO:0062177). GO:0062177 is a biological process from the Gene Ontology.
Radial spoke 3 GO:0120335 Gene Ontology (GO) Relation: this pathophysiological event involves this cellular component This pathophysiological event involves Radial spoke 3 (GO:0120335). GO:0120335 is a cellular component from the Gene Ontology.
Downstream
Sperm Axonemal Disorganization Radial spokes anchor the central pair and connect it to the dynein arms; without RS3 the central pair is lost and the axoneme becomes unstable during flagellar assembly. How loss of one spoke leads to wholesale disorganization of the flagellum in sperm, but not in most motile cilia, is not established.
Show evidence (3 references)
PMID:25694453 SUPPORT Model organism
"We show that in Tetrahymena, loss of either FAP61 or FAP251 reduces cell swimming and affects the ciliary waveform and that RS3 is either missing or incomplete, whereas RS1 and RS2 are unaffected."
CSC subunits are needed specifically for RS3 assembly.
PMID:32161152 SUPPORT Human clinical
"Moreover, we confirmed that the WDR66 protein is a physical and functional partner of CFAP91 into the CSC."
CFAP251 and CFAP91 are partners in the human sperm CSC.
PMID:35174165 SUPPORT Human clinical
"Furthermore, we observed a complete absence of CFAP251 proteins in the sperm tails of the patients with CFAP61 variants, indicating that CFAP61 is essential for the localization of CFAP251 in sperm flagella."
CFAP251 depends on its CSC partner CFAP61 in human sperm.
Sperm Axonemal Disorganization
Flagellar cross-sections show loss of the central pair and radial spokes with disordered doublets and outer dense fibers; longitudinal sections show disorganized outer dense fibers, fibrous sheath and mitochondrial sheath, sometimes with flagella replaced by a cytoplasmic mass of unassembled components. The mitochondrial sheath defect is prominent, giving sperm that appear to lack mitochondria.
Sperm CL:0000019 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves Sperm (CL:0000019). CL:0000019 is a cell type from the Cell Ontology.
Sperm mitochondrial sheath assembly GO:0120317 ↓ DECREASED Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased Sperm mitochondrial sheath assembly (GO:0120317). GO:0120317 is a biological process from the Gene Ontology.
Axoneme GO:0005930 Gene Ontology (GO) Relation: this pathophysiological event involves this cellular component This pathophysiological event involves Axoneme (GO:0005930). GO:0005930 is a cellular component from the Gene Ontology. Sperm mitochondrial sheath GO:0097226 Gene Ontology (GO) Relation: this pathophysiological event involves this cellular component This pathophysiological event involves Sperm mitochondrial sheath (GO:0097226). GO:0097226 is a cellular component from the Gene Ontology.
Animal models
Cfap251 knockout mouse Mouse recapitulates The knockout reproduces the central pair and radial spoke loss and the mitochondrial sheath defect.
Downstream
Multiple Morphological Abnormalities of the Sperm Flagella
Abnormal sperm axoneme morphology
Show evidence (4 references)
PMID:41943837 SUPPORT Human clinical
"However, various axonemal anomalies were observed in the spermatozoa from F1 IV-1 and F2 II-1, including disordered ODFs and DMTs lacking RS and CP (Figure 6E)."
Central pair and radial spoke loss in patient sperm.
PMID:30122540 SUPPORT Human clinical
"Longitudinal sections showed severe axonemal and peri-axonemal defects affecting the outer dense fibers (ODFs), the fibrous sheath (FS), and the mitochondrial sheath (MS), which appeared completely disorganized, resulting in aborted flagella or their replacement by a cytoplasmic mass englobing..."
Peri-axonemal disorganization in a man homozygous for the founder deletion.
PMID:30122541 SUPPORT Human clinical
"Using immunofluorescent and transmission electron microscopy, we provide evidence that loss of CFAP251 affects the formation of the mitochondrial sheath."
Mitochondrial sheath defect in patient sperm.
+ 1 more reference
Multiple Morphological Abnormalities of the Sperm Flagella
Absent, short, coiled, bent and irregular-caliber flagella in the same ejaculate, with motility usually absent or severely reduced. Some patients keep a minority of normal flagella and a little motility. Sperm concentration is usually normal.
Sperm CL:0000019 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves Sperm (CL:0000019). CL:0000019 is a cell type from the Cell Ontology.
Sperm flagellum assembly GO:0120316 ↓ DECREASED Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased Sperm flagellum assembly (GO:0120316). GO:0120316 is a biological process from the Gene Ontology.
Animal models
Cfap251 knockout mouse Mouse recapitulates Knockout sperm are fully immotile with MMAF.
Downstream
Reduced sperm motility
Male infertility Malformed, immotile sperm cannot reach or fertilize the oocyte in vivo.
Absent sperm flagella
Short sperm flagella
Coiled sperm flagella
Bent sperm flagella
Irregularly shaped sperm tail
Show evidence (2 references)
PMID:30310178 SUPPORT Human clinical
"we employed human whole-exome sequencing for genetic analysis and identified biallelic mutations of CFAP251 (cilia- and flagella-associated protein 251, also known as WDR66) in three (5%) of 65 Han Chinese men with MMAF"
CFAP251 explains part of an MMAF cohort.
PMID:41943837 SUPPORT Human clinical
"SEM further confirmed the MMAF phenotype in most spermatozoa from both probands (Figure 6D)."
Scanning electron microscopy of patient sperm.
⬡

Pathograph

Use Group by to collapse related nodes into one box. Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Spermatogenic Failure 33 Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
●

Phenotypes

8
Male infertility Reproductive HP:0003251 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Male infertility (HP:0003251). HP:0003251 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:30310178 SUPPORT Human clinical
"Our observations suggested that CFAP251 is associated with sperm flagellar development and human male infertility."
Male infertility in CFAP251 carriers.
PMID:41943837 SUPPORT Human clinical
"CFAP251 mutations were identified by whole-exome sequencing on probands from Han Chinese families with primary infertility and MMAF."
Primary infertility in further probands.
Reduced sperm motility Reproductive HP:0012207 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Asthenozoospermia, annotated with Reduced sperm motility (HP:0012207). HP:0012207 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:41943837 SUPPORT Human clinical
"Routine semen analysis of the two probands revealed severe teratoasthenospermia with complete loss of sperm motility (Table 1)."
Absent motility in two probands.
PMID:35087568 SUPPORT Human clinical
"It is worth noting that not all the flagella of the patient were abnormal, which made the patient’s sperm retain a certain amount of motility."
Some patients retain residual motility.
Absent sperm flagella Reproductive HP:0032558 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Absent sperm flagella (HP:0032558). HP:0032558 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30122540 SUPPORT Human clinical
"In this study, we focused on subjects presenting a typical MMAF phenotype characterized by the presence of immotile sperm with short, bent, coiled, absent flagellum or flagellum with an irregular width (Figure 1)."
The founder-deletion carriers were selected on this sperm phenotype.
Short sperm flagella Reproductive HP:0032559 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Short sperm flagella (HP:0032559). HP:0032559 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30122540 SUPPORT Human clinical
"In this study, we focused on subjects presenting a typical MMAF phenotype characterized by the presence of immotile sperm with short, bent, coiled, absent flagellum or flagellum with an irregular width (Figure 1)."
The founder-deletion carriers were selected on this sperm phenotype.
Coiled sperm flagella Reproductive HP:0032560 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Coiled sperm flagella (HP:0032560). HP:0032560 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30122540 SUPPORT Human clinical
"In this study, we focused on subjects presenting a typical MMAF phenotype characterized by the presence of immotile sperm with short, bent, coiled, absent flagellum or flagellum with an irregular width (Figure 1)."
The founder-deletion carriers were selected on this sperm phenotype.
Bent sperm flagella Reproductive HP:0034811 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Bent sperm flagella (HP:0034811). HP:0034811 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30122540 SUPPORT Human clinical
"In this study, we focused on subjects presenting a typical MMAF phenotype characterized by the presence of immotile sperm with short, bent, coiled, absent flagellum or flagellum with an irregular width (Figure 1)."
The founder-deletion carriers were selected on this sperm phenotype.
Irregularly shaped sperm tail Reproductive HP:0033393 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Irregular-caliber sperm flagella, annotated with Irregularly shaped sperm tail (HP:0033393). HP:0033393 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30122540 SUPPORT Human clinical
"In this study, we focused on subjects presenting a typical MMAF phenotype characterized by the presence of immotile sperm with short, bent, coiled, absent flagellum or flagellum with an irregular width (Figure 1)."
The founder-deletion carriers were selected on this sperm phenotype.
Abnormal sperm axoneme morphology Reproductive HP:0033524 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Abnormal sperm axoneme morphology (HP:0033524). HP:0033524 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:41943837 SUPPORT Human clinical
"However, various axonemal anomalies were observed in the spermatozoa from F1 IV-1 and F2 II-1, including disordered ODFs and DMTs lacking RS and CP (Figure 6E)."
Axonemal ultrastructure defects in patients.
🧬

Genetic Associations

1
CFAP251 (Causal)
Gene: CFAP251 hgnc:28506 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is CFAP251 (hgnc:28506). hgnc:28506 is a gene from the HUGO Gene Nomenclature Committee.
Show evidence (4 references)
PMID:30122541 SUPPORT Human clinical
"the two brothers were homozygous for the frameshift chr12: g.122359334delA (p.Asp42Metfs∗4), and the third individual was compound heterozygous for chr12: g.122359542G>T (p.Glu111∗) and chr12: g.122395032_122395033delCT (p.Leu530Valfs∗4)"
First report of biallelic loss-of-function variants.
PMID:30122540 SUPPORT Human clinical
"The deletion was found in 7 of the 46 Tunisian MMAF subjects analyzed here, indicating that in this population, the WDR66 deletion is responsible for 15% of cases."
Founder deletion explaining a large share of Tunisian MMAF.
PMID:30310178 SUPPORT Human clinical
"All these CFAP251 mutations are loss-of-function."
Independent Han Chinese cohort.
+ 1 more reference
💊

Medical Actions

2
Intracytoplasmic Sperm Injection
Action: Intracytoplasmic Sperm InjectionNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Intracytoplasmic Sperm Injection (NCIT:C185482). NCIT:C185482 is a clinical intervention from the NCI Thesaurus. NCIT:C185482
Platform: Other
ICSI bypasses the motility defect. Clinical pregnancies and live births have been reported with ejaculated sperm, including in men with no motile sperm when viable sperm were selected with the hypo-osmotic swelling test. No fertilization failure has been reported for CFAP251, but the number of treated couples is small.
Mechanism Target:
Multiple Morphological Abnormalities of the Sperm Flagella — Direct injection makes flagellar propulsion and form irrelevant to fertilization.
Show evidence (1 reference)
PMID:41943837 SUPPORT Human clinical
"We also demonstrated that ICSI could overcome infertility in the affected probands, as evidenced by the successful delivery of healthy offspring."
ICSI overcomes the flagellar defect.
Show evidence (3 references)
PMID:41943837 SUPPORT Human clinical
"All four couples (F1 IV-1, F2 II-1, M1 IV-1, and M4 II-1) achieved clinical pregnancy after ICSI treatment and subsequently delivered healthy infants."
Live births in four couples.
PMID:35087568 SUPPORT Human clinical
"Our study was the first ICSI outcome report of a patient with the CFAP251 variant, and the results showed that successful clinical pregnancy could be achieved when the patient harboring the CFAP251 mutation was treated with ICSI."
Clinical pregnancy after ICSI.
PMID:42871648 SUPPORT Human clinical
"Both cases of MMAF patients with SPEF2 and CFAP251 gene mutations reported in this study successfully achieved pregnancy and delivered healthy offspring through HOST combined with ICSI."
Live birth when viable immotile sperm were selected by the hypo-osmotic swelling test.
Genetic Counseling
Action: Genetic CounselingNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Genetic Counseling (NCIT:C15240). NCIT:C15240 is a clinical intervention from the NCI Thesaurus. NCIT:C15240
Platform: Behavioral / lifestyle
Counselling for autosomal recessive recurrence and carrier testing of relatives once the familial CFAP251 alleles are known. Uniparental disomy has been documented, in which only one parent is a carrier, and sons conceived by ICSI inherit one CFAP251 variant.
Show evidence (2 references)
PMID:35087568 SUPPORT Human clinical
"The rare inheritance mode, maternal uniparental disomy, was first reported in MMAF patients, which indicated to us that even if only one parent was a heterozygous variant carrier, the offspring would still suffer a probable risk of MMAF."
Uniparental disomy changes the recurrence risk used in counselling.
PMID:41943837 SUPPORT Human clinical
"Our findings highlight the underlying risk of male infertility and PCD-like ciliary defects associated with CFAP251 and provide a valuable reference for personalized genetic counselling and clinical treatment of affected individuals."
The authors name genetic counselling as an application of the molecular diagnosis.
🔬

Diagnosis

4
Molecular Genetic Testing
Establishes the diagnosis. Probands have been identified by whole-exome sequencing, including copy-number analysis of exome data, which detects the North African exon 20-21 deletion that sequence-variant calling misses.
Genetic Testing NCIT:C15709 NCI Thesaurus (NCIT)
Show evidence (2 references)
PMID:30122540 SUPPORT Human clinical
"Here, we searched for pathological copy-number variants in whole-exome sequencing data from a cohort of 78 MMAF-affected subjects to identify additional genes associated with MMAF."
The founder deletion was found by copy-number analysis of exome data.
PMID:41943837 SUPPORT Human clinical
"CFAP251 mutations were identified by whole-exome sequencing on probands from Han Chinese families with primary infertility and MMAF."
Whole-exome sequencing identified the causal alleles.
Semen Analysis
Shows asthenoteratozoospermia with MMAF, usually with normal sperm concentration and absent or very low motility.
Show evidence (1 reference)
PMID:41943837 SUPPORT Human clinical
"Routine semen analysis of the two probands revealed severe teratoasthenospermia with complete loss of sperm motility (Table 1)."
Semen analysis findings in patients.
Transmission Electron Microscopy of Sperm Flagella
Shows loss of the central pair and radial spokes with disorganized doublets, outer dense fibers, fibrous sheath and mitochondrial sheath.
Transmission Electron Microscopy NCIT:C18216 NCI Thesaurus (NCIT)
Show evidence (1 reference)
PMID:35087568 SUPPORT Human clinical
"Furthermore, under TEM, for sperm flagella, the cross sections of the patient with the CFAP251 variant displayed typical severe disorganization in axonemal and other periaxonemal structures, in contrast to the “9+2” microtubule structure in normal males."
TEM findings in patient sperm.
Immunofluorescence of CFAP251 in Sperm
Absent CFAP251 staining of sperm flagella supports pathogenicity of variants of uncertain significance, such as splice variants.
Show evidence (1 reference)
PMID:35087568 SUPPORT Human clinical
"Simultaneously, western blotting showed the absence of CFAP251 protein translation due to the splicing mutation, and CFAP251 immunostaining was mainly localized at the sperm flagella in normal spermatozoa but was almost absent in the sperm from patients with the CFAP251 variant (Figure 5)."
Immunostaining and immunoblotting confirmed loss of function of a splice variant.
🐁

Animal Models

1
Cfap251 knockout mouse
Knockout males are infertile with fully immotile MMAF sperm, central pair and radial spoke loss, a disorganized mitochondrial sheath and a marked fall in epididymal sperm count. Tracheal cilia keep normal length and density but often lack inner dynein arms.
Species
Mouse
Genotype
Cfap251-/- (knockout, C57BL/6J), homozygous
Publication
PMID:41943837
Pathograph links
Sperm Axonemal Disorganization recapitulates fidelity: high observes: cellular The knockout reproduces the central pair and radial spoke loss and the mitochondrial sheath defect.
Divergences from the human mechanism
species mismatch qualifying
Mouse knockout males have a striking reduction in epididymal sperm count and smaller testes, whereas most men with CFAP251 variants have normal sperm concentration, so mouse spermatogenesis is more sensitive to loss of the protein than human.
Show evidence (2 references)
PMID:41943837 SUPPORT Model organism
"In contrast, sperm from Cfap251-/- mice exhibited severe abnormalities in all analyzed sections, characterized by CP and RS loss (Figure 4F)."
Same ultrastructural lesion as in patients.
+ 1 more reference
Multiple Morphological Abnormalities of the Sperm Flagella recapitulates fidelity: high observes: cellular Knockout sperm are fully immotile with MMAF.
Show evidence (1 reference)
PMID:41943837 SUPPORT Model organism
"The cauda epididymal spermatozoa of Cfap251-/- males were 100% immotile compared with those of Cfap251+/+ (Figure 2J and K)."
Immotile sperm in knockout males.
{ }

Source YAML

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name: Spermatogenic Failure 33
creation_date: "2026-10-16T00:00:00Z"
category: Mendelian
synonyms:
- SPGF33
- spermatogenic failure 33
- CFAP251-related multiple morphological abnormalities of the sperm flagella
- WDR66-related multiple morphological abnormalities of the sperm flagella
description: >-
  Spermatogenic failure 33 (SPGF33) is autosomal recessive male infertility
  caused by biallelic loss-of-function variants in CFAP251 (formerly WDR66).
  CFAP251 is a WD-repeat subunit of the calmodulin- and spoke-associated complex
  (CSC), which with CFAP61 and CFAP91 builds the base of radial spoke 3 (RS3) on
  the peripheral microtubule doublets of the axoneme. In the absence of
  CFAP251 the CSC and RS3 fail to assemble in sperm, the developing flagellum is
  disorganized, and men present with asthenoteratozoospermia with multiple
  morphological abnormalities of the sperm flagella (MMAF): absent, short,
  coiled, bent and irregular-caliber flagella with low or absent motility.
  Electron microscopy shows loss of the central pair and radial spokes,
  disorganized doublets, outer dense fibers and fibrous sheath, and a defective
  mitochondrial sheath.

  A recurrent C-terminal deletion of exons 20-21 is a founder allele in North
  Africa and explains about 15% of MMAF in Tunisian men. Most patients have no
  respiratory symptoms, but one 2026 report described a cough and chest CT
  changes in one patient and inner dynein arm loss in tracheal cilia of
  knockout mice. Intracytoplasmic sperm injection (ICSI) has produced
  pregnancies and live births.
disease_term:
  preferred_term: spermatogenic failure 33
  term:
    id: MONDO:0029147
    label: spermatogenic failure 33
parents:
- Spermatogenic Failure
- Genetic Disease
notes: >-
  MONDO cross-references the phenotype as OMIM 618152. ClinGen has not
  classified CFAP251 for spermatogenic failure 33: no CFAP251 row is present in
  the ClinGen gene-disease validity export dated 2026-10-14
  (data/clingen/gene_validity.csv), so gene_disease_validity is left absent.
  The CFAP251 report in PMID:42871648 is a compound heterozygote whose phase
  could not be confirmed because parental samples were unavailable. A 2023
  study of CFAP61 knockdown in Leydig cells is not used here because it does
  not concern CFAP251. The Trypanosoma and Tetrahymena orthologue studies are
  cited as evidence for the conserved position of CFAP251 in the radial spoke 3
  base; neither organism has sperm. No GeneReviews chapter covers this disease
  (Bookshelf index snapshot 2026-09-10).
inheritance:
- name: Autosomal recessive
  description: >-
    Disease requires biallelic CFAP251 variants: homozygous variants in
    consanguineous and founder-allele families, and compound heterozygous
    variants. One proband with a homozygous splice variant inherited both copies
    from his mother through maternal uniparental disomy.
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  evidence:
  - reference: PMID:30122541
    reference_title: "Loss of Calmodulin- and Radial-Spoke-Associated Complex Protein CFAP251 Leads to Immotile Spermatozoa Lacking Mitochondria and Infertility in Men."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In three men, we found bi-allelic loss-of-function mutations in WDR66, encoding cilia- and flagella-associated protein 251 (CFAP251)"
    explanation: Biallelic loss-of-function variants in affected men.
  - reference: PMID:35087568
    reference_title: "Successful Results of Intracytoplasmic Sperm Injection of a Chinese Patient With Multiple Morphological Abnormalities of Sperm Flagella Caused by a Novel Splicing Mutation in CFAP251."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Interestingly, the patient's mother was a heterozygous carrier for the mutation, but his father was not, and finally, the inheritance pattern was proven to be maternal uniparental disomy."
    explanation: Homozygosity arising through maternal uniparental disomy, a recessive mechanism with a different recurrence risk.
pathophysiology:
- name: Loss of CFAP251
  description: >-
    Frameshift, nonsense, splice-site and large C-terminal deletion alleles
    abolish or sharply reduce CFAP251 in sperm. CFAP251 is normally present
    along the whole flagellum, with a sperm-specific isoform produced during
    maturation. It is a structural WD-repeat scaffold of the calmodulin- and
    spoke-associated complex at the base of radial spoke 3.
  biological_scale: MOLECULAR
  genes:
  - preferred_term: CFAP251
    term:
      id: hgnc:28506
      label: CFAP251
  molecular_functions:
  - preferred_term: structural constituent of the axonemal cytoskeleton
    modifier: DECREASED
    term:
      id: GO:0005200
      label: structural constituent of cytoskeleton
  cellular_components:
  - preferred_term: Radial spoke base 3
    term:
      id: GO:0120342
      label: radial spoke base 3
  downstream:
  - target: Loss of the Calmodulin- and Spoke-Associated Complex from the Sperm Axoneme
    causal_link_type: DIRECT
    description: >-
      CFAP251 is itself a CSC subunit; without it the arch-like density at the
      base of RS3 is missing and the spoke is incomplete.
    evidence:
    - reference: PMID:25694453
      reference_title: "The CSC proteins FAP61 and FAP251 build the basal substructures of radial spoke 3 in cilia."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Specifically, FAP251-null cilia lack an arch-like density at the RS3 base, whereas FAP61-null cilia lack an adjacent portion of the RS3 stem region."
      explanation: >-
        Cryo-electron tomography of Tetrahymena cilia locates the orthologue
        at the RS3 base and shows that RS3 fails to assemble without it.
  - target: Reduced TUBB4B and SLC25A4 Recruitment to the Sperm Flagellum
    causal_link_type: DIRECT
    hypothesis_groups:
    - cfap251_tubb4b_slc25a4_recruitment
    description: >-
      CFAP251 binds beta-tubulin TUBB4B and the mitochondrial ADP/ATP carrier
      SLC25A4; without it both proteins are reduced in testis and along the
      sperm flagellum.
    evidence:
    - reference: PMID:41943837
      reference_title: "CFAP251 Deficiency Induces Male Infertility and PCD-like Ciliary Defects by Disrupting TUBB4B and SLC25A4 Recruitment in Humans and Mice."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Co-IP assays demonstrated strong interactions between TUBB4B, SLC25A4, and CFAP251 in vitro (Figure 6F and G)"
      explanation: Co-immunoprecipitation of CFAP251 with TUBB4B and SLC25A4.
    - reference: PMID:41943837
      reference_title: "CFAP251 Deficiency Induces Male Infertility and PCD-like Ciliary Defects by Disrupting TUBB4B and SLC25A4 Recruitment in Humans and Mice."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "The levels of TUBB4B and SLC25A4 were reduced in Cfap251-/- testes, whereas CABYR and AKAP3 levels were unaffected (Figure 6H and I)."
      explanation: Both binding partners fall in knockout testis while two weaker interactors do not.
    - reference: PMID:41943837
      reference_title: "CFAP251 Deficiency Induces Male Infertility and PCD-like Ciliary Defects by Disrupting TUBB4B and SLC25A4 Recruitment in Humans and Mice."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The results revealed a significant downregulation of the colocalization signals for both TUBB4B and SLC25A4 in the sperm flagellum (Supplementary Figure 9A and B)."
      explanation: Immunofluorescence of sperm from patients with CFAP251 splice variants shows the same reduction.
  evidence:
  - reference: PMID:30122541
    reference_title: "Loss of Calmodulin- and Radial-Spoke-Associated Complex Protein CFAP251 Leads to Immotile Spermatozoa Lacking Mitochondria and Infertility in Men."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We show that CFAP251 is normally located along the flagellum but is absent in men carrying WDR66 mutations and reveal a spermatozoa-specific isoform probably generated during spermatozoon maturation."
    explanation: Patient sperm lack CFAP251.
  - reference: PMID:41943837
    reference_title: "CFAP251 Deficiency Induces Male Infertility and PCD-like Ciliary Defects by Disrupting TUBB4B and SLC25A4 Recruitment in Humans and Mice."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Furthermore, CFAP251 was detected along the length of the flagella in spermatozoa from the control individuals but was absent in those of F1 IV-1 and F2 II-1, confirming a complete loss of CFAP251 (Figure 6F)."
    explanation: Homozygous splice alleles remove CFAP251 from sperm.
  - reference: PMID:30122540
    reference_title: "A Homozygous Ancestral SVA-Insertion-Mediated Deletion in WDR66 Induces Multiple Morphological Abnormalities of the Sperm Flagellum and Male Infertility."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "It was found in seven apparently unrelated North African individuals and removed exons 20 and 21 out of 22 of WDR66."
    explanation: The founder deletion removes the C-terminal region of the protein.
- name: Reduced TUBB4B and SLC25A4 Recruitment to the Sperm Flagellum
  description: >-
    Co-immunoprecipitation and mass spectrometry of mouse testis identified the
    beta-tubulin TUBB4B and the mitochondrial ADP/ATP carrier SLC25A4 as CFAP251
    partners, and both co-immunoprecipitate with CFAP251 in vitro. In elongating spermatids
    both colocalize with tubulin, and in mature sperm TUBB4B is enriched in the
    principal piece and SLC25A4 in the midpiece. Both proteins are reduced in
    Cfap251 knockout testis and along knockout sperm flagella, and their
    flagellar signal is reduced in sperm of men with CFAP251 splice variants.
    The authors propose that CFAP251 is a scaffold for the stable
    incorporation of TUBB4B and SLC25A4 into the flagellum; this rests on one
    study.
  biological_scale: MOLECULAR
  genes:
  - preferred_term: TUBB4B
    term:
      id: hgnc:20771
      label: TUBB4B
  - preferred_term: SLC25A4
    term:
      id: hgnc:10990
      label: SLC25A4
  molecular_functions:
  - preferred_term: TUBB4B structural constituent of the flagellar cytoskeleton
    modifier: DECREASED
    term:
      id: GO:0005200
      label: structural constituent of cytoskeleton
  - preferred_term: SLC25A4 ADP/ATP exchange
    modifier: DECREASED
    term:
      id: GO:0005471
      label: ATP:ADP antiporter activity
  cell_types:
  - preferred_term: Sperm
    term:
      id: CL:0000019
      label: sperm
  cellular_components:
  - preferred_term: Sperm flagellum
    term:
      id: GO:0036126
      label: sperm flagellum
  downstream:
  - target: Sperm Axonemal Disorganization
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - cfap251_tubb4b_slc25a4_recruitment
    description: >-
      Proposed to contribute to flagellar disorganization and, through
      SLC25A4, to the midpiece energy-supply defect. Which part of the
      axonemal and mitochondrial sheath phenotype depends on these two
      proteins, rather than on radial spoke 3 loss, has not been tested.
    evidence:
    - reference: PMID:41943837
      reference_title: "CFAP251 Deficiency Induces Male Infertility and PCD-like Ciliary Defects by Disrupting TUBB4B and SLC25A4 Recruitment in Humans and Mice."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Given that CFAP251 deficiency caused diminished immunofluorescence signals for TUBB4B and SLC25A4 in the sperm flagella of mice (Figures 5K and M), we propose that the interaction between CFAP251, TUBB4B, and SLC25A4 is required for flagellar development during spermiogenesis."
      explanation: The authors' proposal, from reduced flagellar TUBB4B and SLC25A4 in knockout mice.
  evidence:
  - reference: PMID:41943837
    reference_title: "CFAP251 Deficiency Induces Male Infertility and PCD-like Ciliary Defects by Disrupting TUBB4B and SLC25A4 Recruitment in Humans and Mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In mature spermatozoa, TUBB4B and SLC25A4 labeling was observed along the entire flagellum, with TUBB4B signal enriched in the principal piece and SLC25A4 concentrated in the midpiece (Figures 5J and L)."
    explanation: Flagellar localization of both partners in mouse sperm.
  - reference: PMID:41943837
    reference_title: "CFAP251 Deficiency Induces Male Infertility and PCD-like Ciliary Defects by Disrupting TUBB4B and SLC25A4 Recruitment in Humans and Mice."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The results revealed a significant downregulation of the colocalization signals for both TUBB4B and SLC25A4 in the sperm flagellum (Supplementary Figure 9A and B)."
    explanation: Reduced flagellar TUBB4B and SLC25A4 in patient sperm.
- name: Loss of the Calmodulin- and Spoke-Associated Complex from the Sperm Axoneme
  description: >-
    The CSC (CFAP61, CFAP91 and CFAP251 with calmodulin) sits at the base of
    radial spoke 3 and links it to the doublet microtubules. Loss of any one
    subunit destabilizes the others: CFAP251 is lost from sperm of men with
    CFAP61 variants and from Cfap91 knockout sperm, and in Cfap251 knockout
    mice the radial spoke proteins RSPH1 and RSPH3 are reduced along the
    flagellum. Radial spoke 3 therefore fails to assemble.
  biological_scale: MOLECULAR
  cellular_components:
  - preferred_term: Radial spoke 3
    term:
      id: GO:0120335
      label: radial spoke 3
  biological_processes:
  - preferred_term: Radial spoke assembly
    modifier: DECREASED
    term:
      id: GO:0062177
      label: radial spoke assembly
  downstream:
  - target: Sperm Axonemal Disorganization
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Radial spokes anchor the central pair and connect it to the dynein arms;
      without RS3 the central pair is lost and the axoneme becomes unstable
      during flagellar assembly. How loss of one spoke leads to wholesale
      disorganization of the flagellum in sperm, but not in most motile cilia,
      is not established.
    evidence:
    - reference: PMID:41943837
      reference_title: "CFAP251 Deficiency Induces Male Infertility and PCD-like Ciliary Defects by Disrupting TUBB4B and SLC25A4 Recruitment in Humans and Mice."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Our findings revealed decreased or completely absent expression of CP-related protein SPAG6, RS-related proteins RSPH1 and RSPH3, ODA-related protein DNAI2, and ODF-related protein ODF2 in the sperm of Cfap251-/- mice compared with that of controls."
      explanation: In knockout mice, central-pair, radial spoke, outer-arm and outer dense fiber proteins are all reduced.
  evidence:
  - reference: PMID:25694453
    reference_title: "The CSC proteins FAP61 and FAP251 build the basal substructures of radial spoke 3 in cilia."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "We show that in Tetrahymena, loss of either FAP61 or FAP251 reduces cell swimming and affects the ciliary waveform and that RS3 is either missing or incomplete, whereas RS1 and RS2 are unaffected."
    explanation: CSC subunits are needed specifically for RS3 assembly.
  - reference: PMID:32161152
    reference_title: "Biallelic variants in MAATS1 encoding CFAP91, a calmodulin-associated and spoke-associated complex protein, cause severe astheno-teratozoospermia and male infertility."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Moreover, we confirmed that the WDR66 protein is a physical and functional partner of CFAP91 into the CSC."
    explanation: CFAP251 and CFAP91 are partners in the human sperm CSC.
  - reference: PMID:35174165
    reference_title: "Biallelic Variants in CFAP61 Cause Multiple Morphological Abnormalities of the Flagella and Male Infertility."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Furthermore, we observed a complete absence of CFAP251 proteins in the sperm tails of the patients with CFAP61 variants, indicating that CFAP61 is essential for the localization of CFAP251 in sperm flagella."
    explanation: CFAP251 depends on its CSC partner CFAP61 in human sperm.
- name: Sperm Axonemal Disorganization
  description: >-
    Flagellar cross-sections show loss of the central pair and radial spokes
    with disordered doublets and outer dense fibers; longitudinal sections show
    disorganized outer dense fibers, fibrous sheath and mitochondrial sheath,
    sometimes with flagella replaced by a cytoplasmic mass of unassembled
    components. The mitochondrial sheath defect is prominent, giving sperm that
    appear to lack mitochondria.
  biological_scale: CELLULAR
  cell_types:
  - preferred_term: Sperm
    term:
      id: CL:0000019
      label: sperm
  cellular_components:
  - preferred_term: Axoneme
    term:
      id: GO:0005930
      label: axoneme
  - preferred_term: Sperm mitochondrial sheath
    term:
      id: GO:0097226
      label: sperm mitochondrial sheath
  biological_processes:
  - preferred_term: Sperm mitochondrial sheath assembly
    modifier: DECREASED
    term:
      id: GO:0120317
      label: sperm mitochondrial sheath assembly
  downstream:
  - target: Multiple Morphological Abnormalities of the Sperm Flagella
    causal_link_type: DIRECT
  - target: Abnormal sperm axoneme morphology
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:41943837
    reference_title: "CFAP251 Deficiency Induces Male Infertility and PCD-like Ciliary Defects by Disrupting TUBB4B and SLC25A4 Recruitment in Humans and Mice."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "However, various axonemal anomalies were observed in the spermatozoa from F1 IV-1 and F2 II-1, including disordered ODFs and DMTs lacking RS and CP (Figure 6E)."
    explanation: Central pair and radial spoke loss in patient sperm.
  - reference: PMID:30122540
    reference_title: "A Homozygous Ancestral SVA-Insertion-Mediated Deletion in WDR66 Induces Multiple Morphological Abnormalities of the Sperm Flagellum and Male Infertility."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Longitudinal sections showed severe axonemal and peri-axonemal defects affecting the outer dense fibers (ODFs), the fibrous sheath (FS), and the mitochondrial sheath (MS), which appeared completely disorganized, resulting in aborted flagella or their replacement by a cytoplasmic mass englobing unassembled axonemal components (data not shown)."
    explanation: Peri-axonemal disorganization in a man homozygous for the founder deletion.
  - reference: PMID:30122541
    reference_title: "Loss of Calmodulin- and Radial-Spoke-Associated Complex Protein CFAP251 Leads to Immotile Spermatozoa Lacking Mitochondria and Infertility in Men."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Using immunofluorescent and transmission electron microscopy, we provide evidence that loss of CFAP251 affects the formation of the mitochondrial sheath."
    explanation: Mitochondrial sheath defect in patient sperm.
  - reference: PMID:35087568
    reference_title: "Successful Results of Intracytoplasmic Sperm Injection of a Chinese Patient With Multiple Morphological Abnormalities of Sperm Flagella Caused by a Novel Splicing Mutation in CFAP251."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Furthermore, under TEM, for sperm flagella, the cross sections of the patient with the CFAP251 variant displayed typical severe disorganization in axonemal and other periaxonemal structures, in contrast to the “9+2” microtubule structure in normal males."
    explanation: Independent patient with the same ultrastructural picture.
- name: Multiple Morphological Abnormalities of the Sperm Flagella
  description: >-
    Absent, short, coiled, bent and irregular-caliber flagella in the same
    ejaculate, with motility usually absent or severely reduced. Some patients
    keep a minority of normal flagella and a little motility. Sperm
    concentration is usually normal.
  biological_scale: CELLULAR
  cell_types:
  - preferred_term: Sperm
    term:
      id: CL:0000019
      label: sperm
  biological_processes:
  - preferred_term: Sperm flagellum assembly
    modifier: DECREASED
    term:
      id: GO:0120316
      label: sperm flagellum assembly
  downstream:
  - target: Reduced sperm motility
    causal_link_type: DIRECT
  - target: Male infertility
    causal_link_type: DIRECT
    description: Malformed, immotile sperm cannot reach or fertilize the oocyte in vivo.
  - target: Absent sperm flagella
    causal_link_type: DIRECT
  - target: Short sperm flagella
    causal_link_type: DIRECT
  - target: Coiled sperm flagella
    causal_link_type: DIRECT
  - target: Bent sperm flagella
    causal_link_type: DIRECT
  - target: Irregularly shaped sperm tail
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:30310178
    reference_title: "Biallelic mutations of CFAP251 cause sperm flagellar defects and human male infertility."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we employed human whole-exome sequencing for genetic analysis and identified biallelic mutations of CFAP251 (cilia- and flagella-associated protein 251, also known as WDR66) in three (5%) of 65 Han Chinese men with MMAF"
    explanation: CFAP251 explains part of an MMAF cohort.
  - reference: PMID:41943837
    reference_title: "CFAP251 Deficiency Induces Male Infertility and PCD-like Ciliary Defects by Disrupting TUBB4B and SLC25A4 Recruitment in Humans and Mice."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "SEM further confirmed the MMAF phenotype in most spermatozoa from both probands (Figure 6D)."
    explanation: Scanning electron microscopy of patient sperm.
mechanistic_hypotheses:
- hypothesis_group_id: cfap251_sperm_restricted
  hypothesis_label: CFAP251 loss causes isolated male infertility rather than primary ciliary dyskinesia
  status: CANONICAL
  description: >-
    CFAP251 is expressed in both testis and airway, but almost all reported
    patients have isolated infertility, and a health questionnaire for PCD
    manifestations was negative in the founder-deletion cohort. In 2026 one
    patient with a homozygous splice variant was reported with tinnitus, a
    seasonal cough and chest CT changes (increased lung markings and a
    pulmonary bulla), and Cfap251 knockout mice had frequent loss of inner
    dynein arms in tracheal cilia. The human evidence for a respiratory
    phenotype is a single patient without ciliary biopsy, beat analysis or
    nasal nitric oxide, so the PCD-like phenotype is unconfirmed, and it is not
    recorded as a disease phenotype here.
  evidence:
  - reference: PMID:30122540
    reference_title: "A Homozygous Ancestral SVA-Insertion-Mediated Deletion in WDR66 Induces Multiple Morphological Abnormalities of the Sperm Flagellum and Male Infertility."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All subjects had an isolated MMAF phenotype and no mention of any other PCD symptoms."
    explanation: No PCD manifestations in a cohort that included seven homozygous founder-deletion carriers.
  - reference: PMID:41943837
    reference_title: "CFAP251 Deficiency Induces Male Infertility and PCD-like Ciliary Defects by Disrupting TUBB4B and SLC25A4 Recruitment in Humans and Mice."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "Notably, one patient carrying biallelic CFAP251 mutations showed PCD-like symptoms, including tinnitus, seasonal cough, and radiological findings of coarsened lung markings and a solitary pulmonary bulla associated with chronic bronchitic inflammation."
    explanation: A single patient with respiratory symptoms and CT changes, without ciliary investigation.
  - reference: PMID:41943837
    reference_title: "CFAP251 Deficiency Induces Male Infertility and PCD-like Ciliary Defects by Disrupting TUBB4B and SLC25A4 Recruitment in Humans and Mice."
    supports: REFUTE
    evidence_source: MODEL_ORGANISM
    snippet: "Although the loss of CFAP251 in the respiratory cilia of Cfap251-/- mice did not result in overt defects in ciliary length or density, TEM revealed a frequent absence of inner dynein arms within the axoneme."
    explanation: Knockout mice have an ultrastructural defect in tracheal cilia.
  - reference: PMID:41943837
    reference_title: "CFAP251 Deficiency Induces Male Infertility and PCD-like Ciliary Defects by Disrupting TUBB4B and SLC25A4 Recruitment in Humans and Mice."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "Another notable limitation is that while ciliary dynein arm defects are clearly demonstrated in the mouse model (Supplementary Figure 4), human ciliary ultrastructure data could not be generated owing to the unavailability of patient ciliary biopsy samples, meaning the PCD-like phenotype in humans was inferred solely from symptoms and chest CT findings rather than direct morphological evidence."
    explanation: The authors' own statement that the human respiratory phenotype is not confirmed by ciliary studies.
- hypothesis_group_id: cfap251_tubb4b_slc25a4_recruitment
  hypothesis_label: CFAP251 recruits TUBB4B and SLC25A4 to the developing sperm flagellum
  status: EMERGING
  description: >-
    A single 2026 study found that CFAP251 binds the beta-tubulin TUBB4B and
    the mitochondrial ADP/ATP carrier SLC25A4 (testis pull-down with mass
    spectrometry, co-immunoprecipitation in vitro, and structural modelling),
    that both proteins are reduced in Cfap251 knockout testis and along
    knockout sperm flagella, and that their flagellar immunofluorescence is
    reduced in sperm of two men with homozygous CFAP251 splice variants. The
    authors propose that CFAP251 is a scaffold needed to incorporate both
    proteins into the flagellum, which would add a tubulin-supply and an
    energy-transport component to the radial spoke 3 defect. It has not been
    replicated, and no experiment separates the contribution of these two
    proteins from that of radial spoke loss.
  evidence:
  - reference: PMID:41943837
    reference_title: "CFAP251 Deficiency Induces Male Infertility and PCD-like Ciliary Defects by Disrupting TUBB4B and SLC25A4 Recruitment in Humans and Mice."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Co-IP assays demonstrated strong interactions between TUBB4B, SLC25A4, and CFAP251 in vitro (Figure 6F and G)"
    explanation: Physical interaction of CFAP251 with both partners.
  - reference: PMID:41943837
    reference_title: "CFAP251 Deficiency Induces Male Infertility and PCD-like Ciliary Defects by Disrupting TUBB4B and SLC25A4 Recruitment in Humans and Mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The levels of TUBB4B and SLC25A4 were reduced in Cfap251-/- testes, whereas CABYR and AKAP3 levels were unaffected (Figure 6H and I)."
    explanation: Loss of both partners in knockout testis.
  - reference: PMID:41943837
    reference_title: "CFAP251 Deficiency Induces Male Infertility and PCD-like Ciliary Defects by Disrupting TUBB4B and SLC25A4 Recruitment in Humans and Mice."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The results revealed a significant downregulation of the colocalization signals for both TUBB4B and SLC25A4 in the sperm flagellum (Supplementary Figure 9A and B)."
    explanation: The same reduction in patient sperm.
phenotypes:
- category: Reproductive
  name: Male infertility
  description: Primary male infertility is the presenting complaint.
  phenotype_term:
    preferred_term: Male infertility
    term:
      id: HP:0003251
      label: Male infertility
  evidence:
  - reference: PMID:30310178
    reference_title: "Biallelic mutations of CFAP251 cause sperm flagellar defects and human male infertility."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our observations suggested that CFAP251 is associated with sperm flagellar development and human male infertility."
    explanation: Male infertility in CFAP251 carriers.
  - reference: PMID:41943837
    reference_title: "CFAP251 Deficiency Induces Male Infertility and PCD-like Ciliary Defects by Disrupting TUBB4B and SLC25A4 Recruitment in Humans and Mice."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "CFAP251 mutations were identified by whole-exome sequencing on probands from Han Chinese families with primary infertility and MMAF."
    explanation: Primary infertility in further probands.
- category: Reproductive
  name: Reduced sperm motility
  description: >-
    Motility is usually absent; a minority of patients retain a few motile
    sperm because not every flagellum is malformed.
  phenotype_term:
    preferred_term: Asthenozoospermia
    term:
      id: HP:0012207
      label: Reduced sperm motility
  evidence:
  - reference: PMID:41943837
    reference_title: "CFAP251 Deficiency Induces Male Infertility and PCD-like Ciliary Defects by Disrupting TUBB4B and SLC25A4 Recruitment in Humans and Mice."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Routine semen analysis of the two probands revealed severe teratoasthenospermia with complete loss of sperm motility (Table 1)."
    explanation: Absent motility in two probands.
  - reference: PMID:35087568
    reference_title: "Successful Results of Intracytoplasmic Sperm Injection of a Chinese Patient With Multiple Morphological Abnormalities of Sperm Flagella Caused by a Novel Splicing Mutation in CFAP251."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "It is worth noting that not all the flagella of the patient were abnormal, which made the patient’s sperm retain a certain amount of motility."
    explanation: Some patients retain residual motility.
- category: Reproductive
  name: Absent sperm flagella
  description: Some sperm lack a flagellum, as part of the MMAF mosaic.
  phenotype_term:
    preferred_term: Absent sperm flagella
    term:
      id: HP:0032558
      label: Absent sperm flagella
  evidence:
  - reference: PMID:30122540
    reference_title: "A Homozygous Ancestral SVA-Insertion-Mediated Deletion in WDR66 Induces Multiple Morphological Abnormalities of the Sperm Flagellum and Male Infertility."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In this study, we focused on subjects presenting a typical MMAF phenotype characterized by the presence of immotile sperm with short, bent, coiled, absent flagellum or flagellum with an irregular width (Figure 1)."
    explanation: The founder-deletion carriers were selected on this sperm phenotype.
- category: Reproductive
  name: Short sperm flagella
  description: Shortened flagella are part of the MMAF mosaic.
  phenotype_term:
    preferred_term: Short sperm flagella
    term:
      id: HP:0032559
      label: Short sperm flagella
  evidence:
  - reference: PMID:30122540
    reference_title: "A Homozygous Ancestral SVA-Insertion-Mediated Deletion in WDR66 Induces Multiple Morphological Abnormalities of the Sperm Flagellum and Male Infertility."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In this study, we focused on subjects presenting a typical MMAF phenotype characterized by the presence of immotile sperm with short, bent, coiled, absent flagellum or flagellum with an irregular width (Figure 1)."
    explanation: The founder-deletion carriers were selected on this sperm phenotype.
- category: Reproductive
  name: Coiled sperm flagella
  description: Coiled flagella are part of the MMAF mosaic.
  phenotype_term:
    preferred_term: Coiled sperm flagella
    term:
      id: HP:0032560
      label: Coiled sperm flagella
  evidence:
  - reference: PMID:30122540
    reference_title: "A Homozygous Ancestral SVA-Insertion-Mediated Deletion in WDR66 Induces Multiple Morphological Abnormalities of the Sperm Flagellum and Male Infertility."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In this study, we focused on subjects presenting a typical MMAF phenotype characterized by the presence of immotile sperm with short, bent, coiled, absent flagellum or flagellum with an irregular width (Figure 1)."
    explanation: The founder-deletion carriers were selected on this sperm phenotype.
- category: Reproductive
  name: Bent sperm flagella
  description: Bent flagella are part of the MMAF mosaic.
  phenotype_term:
    preferred_term: Bent sperm flagella
    term:
      id: HP:0034811
      label: Bent sperm flagella
  evidence:
  - reference: PMID:30122540
    reference_title: "A Homozygous Ancestral SVA-Insertion-Mediated Deletion in WDR66 Induces Multiple Morphological Abnormalities of the Sperm Flagellum and Male Infertility."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In this study, we focused on subjects presenting a typical MMAF phenotype characterized by the presence of immotile sperm with short, bent, coiled, absent flagellum or flagellum with an irregular width (Figure 1)."
    explanation: The founder-deletion carriers were selected on this sperm phenotype.
- category: Reproductive
  name: Irregularly shaped sperm tail
  description: Irregular-caliber flagella are part of the MMAF mosaic.
  phenotype_term:
    preferred_term: Irregular-caliber sperm flagella
    term:
      id: HP:0033393
      label: Irregularly shaped sperm tail
  evidence:
  - reference: PMID:30122540
    reference_title: "A Homozygous Ancestral SVA-Insertion-Mediated Deletion in WDR66 Induces Multiple Morphological Abnormalities of the Sperm Flagellum and Male Infertility."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In this study, we focused on subjects presenting a typical MMAF phenotype characterized by the presence of immotile sperm with short, bent, coiled, absent flagellum or flagellum with an irregular width (Figure 1)."
    explanation: The founder-deletion carriers were selected on this sperm phenotype.
- category: Reproductive
  name: Abnormal sperm axoneme morphology
  description: >-
    Electron microscopy shows loss of the central pair and radial spokes and
    disordered doublets, outer dense fibers and mitochondrial sheath.
  phenotype_term:
    preferred_term: Abnormal sperm axoneme morphology
    term:
      id: HP:0033524
      label: Abnormal sperm axoneme morphology
  evidence:
  - reference: PMID:41943837
    reference_title: "CFAP251 Deficiency Induces Male Infertility and PCD-like Ciliary Defects by Disrupting TUBB4B and SLC25A4 Recruitment in Humans and Mice."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "However, various axonemal anomalies were observed in the spermatozoa from F1 IV-1 and F2 II-1, including disordered ODFs and DMTs lacking RS and CP (Figure 6E)."
    explanation: Axonemal ultrastructure defects in patients.
genetic:
- name: CFAP251
  association: Causal
  gene_term:
    preferred_term: CFAP251
    term:
      id: hgnc:28506
      label: CFAP251
  notes: >-
    Reported alleles include frameshift (p.Asp42Metfs*4, p.Leu530Valfs*4),
    nonsense (p.Glu111*), splice-site (c.1192-3C>G, c.1535+1G>C,
    c.1269+2T>C) variants and a homozygous deletion of exons 20-21 mediated by
    an SVA retrotransposon insertion. The deletion is a North African founder
    allele found in 7 of 46 Tunisian MMAF patients. ClinGen has not classified
    this gene-disease pair.
  evidence:
  - reference: PMID:30122541
    reference_title: "Loss of Calmodulin- and Radial-Spoke-Associated Complex Protein CFAP251 Leads to Immotile Spermatozoa Lacking Mitochondria and Infertility in Men."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the two brothers were homozygous for the frameshift chr12: g.122359334delA (p.Asp42Metfs∗4), and the third individual was compound heterozygous for chr12: g.122359542G>T (p.Glu111∗) and chr12: g.122395032_122395033delCT (p.Leu530Valfs∗4)"
    explanation: First report of biallelic loss-of-function variants.
  - reference: PMID:30122540
    reference_title: "A Homozygous Ancestral SVA-Insertion-Mediated Deletion in WDR66 Induces Multiple Morphological Abnormalities of the Sperm Flagellum and Male Infertility."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The deletion was found in 7 of the 46 Tunisian MMAF subjects analyzed here, indicating that in this population, the WDR66 deletion is responsible for 15% of cases."
    explanation: Founder deletion explaining a large share of Tunisian MMAF.
  - reference: PMID:30310178
    reference_title: "Biallelic mutations of CFAP251 cause sperm flagellar defects and human male infertility."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All these CFAP251 mutations are loss-of-function."
    explanation: Independent Han Chinese cohort.
  - reference: PMID:41943837
    reference_title: "CFAP251 Deficiency Induces Male Infertility and PCD-like Ciliary Defects by Disrupting TUBB4B and SLC25A4 Recruitment in Humans and Mice."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Additionally, we identified two novel homozygous splicing mutations in CFAP251 that cause the loss of CFAP251 protein in patients with MMAF."
    explanation: Further homozygous splice alleles with protein loss.
animal_models:
- name: Cfap251 knockout mouse
  species: Mouse
  genotype: Cfap251-/- (knockout, C57BL/6J), homozygous
  publication: PMID:41943837
  description: >-
    Knockout males are infertile with fully immotile MMAF sperm, central pair
    and radial spoke loss, a disorganized mitochondrial sheath and a marked
    fall in epididymal sperm count. Tracheal cilia keep normal length and
    density but often lack inner dynein arms.
  modeled_mechanisms:
  - target: Sperm Axonemal Disorganization
    relationship: RECAPITULATES
    fidelity: HIGH
    model_scale: CELLULAR
    description: The knockout reproduces the central pair and radial spoke loss and the mitochondrial sheath defect.
    divergences:
    - divergence_type: SPECIES_MISMATCH
      materiality: QUALIFYING
      description: >-
        Mouse knockout males have a striking reduction in epididymal sperm
        count and smaller testes, whereas most men with CFAP251 variants have
        normal sperm concentration, so mouse spermatogenesis is more sensitive
        to loss of the protein than human.
    evidence:
    - reference: PMID:41943837
      reference_title: "CFAP251 Deficiency Induces Male Infertility and PCD-like Ciliary Defects by Disrupting TUBB4B and SLC25A4 Recruitment in Humans and Mice."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "In contrast, sperm from Cfap251-/- mice exhibited severe abnormalities in all analyzed sections, characterized by CP and RS loss (Figure 4F)."
      explanation: Same ultrastructural lesion as in patients.
    - reference: PMID:41943837
      reference_title: "CFAP251 Deficiency Induces Male Infertility and PCD-like Ciliary Defects by Disrupting TUBB4B and SLC25A4 Recruitment in Humans and Mice."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "H&E staining of epididymal sections also showed a striking reduction in the sperm count of Cfap251-/- mice (Figure 2I)."
      explanation: Records the low sperm count behind the species divergence.
  - target: Multiple Morphological Abnormalities of the Sperm Flagella
    relationship: RECAPITULATES
    fidelity: HIGH
    model_scale: CELLULAR
    description: Knockout sperm are fully immotile with MMAF.
    evidence:
    - reference: PMID:41943837
      reference_title: "CFAP251 Deficiency Induces Male Infertility and PCD-like Ciliary Defects by Disrupting TUBB4B and SLC25A4 Recruitment in Humans and Mice."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "The cauda epididymal spermatozoa of Cfap251-/- males were 100% immotile compared with those of Cfap251+/+ (Figure 2J and K)."
      explanation: Immotile sperm in knockout males.
treatments:
- name: Intracytoplasmic Sperm Injection
  description: >-
    ICSI bypasses the motility defect. Clinical pregnancies and live births
    have been reported with ejaculated sperm, including in men with no motile
    sperm when viable sperm were selected with the hypo-osmotic swelling test.
    No fertilization failure has been reported for CFAP251, but the number of
    treated couples is small.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Intracytoplasmic Sperm Injection
    term:
      id: NCIT:C185482
      label: Intracytoplasmic Sperm Injection
  target_mechanisms:
  - target: Multiple Morphological Abnormalities of the Sperm Flagella
    description: Direct injection makes flagellar propulsion and form irrelevant to fertilization.
    evidence:
    - reference: PMID:41943837
      reference_title: "CFAP251 Deficiency Induces Male Infertility and PCD-like Ciliary Defects by Disrupting TUBB4B and SLC25A4 Recruitment in Humans and Mice."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "We also demonstrated that ICSI could overcome infertility in the affected probands, as evidenced by the successful delivery of healthy offspring."
      explanation: ICSI overcomes the flagellar defect.
  evidence:
  - reference: PMID:41943837
    reference_title: "CFAP251 Deficiency Induces Male Infertility and PCD-like Ciliary Defects by Disrupting TUBB4B and SLC25A4 Recruitment in Humans and Mice."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All four couples (F1 IV-1, F2 II-1, M1 IV-1, and M4 II-1) achieved clinical pregnancy after ICSI treatment and subsequently delivered healthy infants."
    explanation: Live births in four couples.
  - reference: PMID:35087568
    reference_title: "Successful Results of Intracytoplasmic Sperm Injection of a Chinese Patient With Multiple Morphological Abnormalities of Sperm Flagella Caused by a Novel Splicing Mutation in CFAP251."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our study was the first ICSI outcome report of a patient with the CFAP251 variant, and the results showed that successful clinical pregnancy could be achieved when the patient harboring the CFAP251 mutation was treated with ICSI."
    explanation: Clinical pregnancy after ICSI.
  - reference: PMID:42871648
    reference_title: "Hypo-osmotic swelling test guided sperm selection followed by intracytoplasmic sperm injection in two men with multiple morphological abnormalities of the sperm flagella associated with SPEF2 and CFAP251 variants: two case reports."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Both cases of MMAF patients with SPEF2 and CFAP251 gene mutations reported in this study successfully achieved pregnancy and delivered healthy offspring through HOST combined with ICSI."
    explanation: Live birth when viable immotile sperm were selected by the hypo-osmotic swelling test.
- name: Genetic Counseling
  description: >-
    Counselling for autosomal recessive recurrence and carrier testing of
    relatives once the familial CFAP251 alleles are known. Uniparental disomy
    has been documented, in which only one parent is a carrier, and sons
    conceived by ICSI inherit one CFAP251 variant.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:35087568
    reference_title: "Successful Results of Intracytoplasmic Sperm Injection of a Chinese Patient With Multiple Morphological Abnormalities of Sperm Flagella Caused by a Novel Splicing Mutation in CFAP251."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The rare inheritance mode, maternal uniparental disomy, was first reported in MMAF patients, which indicated to us that even if only one parent was a heterozygous variant carrier, the offspring would still suffer a probable risk of MMAF."
    explanation: Uniparental disomy changes the recurrence risk used in counselling.
  - reference: PMID:41943837
    reference_title: "CFAP251 Deficiency Induces Male Infertility and PCD-like Ciliary Defects by Disrupting TUBB4B and SLC25A4 Recruitment in Humans and Mice."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our findings highlight the underlying risk of male infertility and PCD-like ciliary defects associated with CFAP251 and provide a valuable reference for personalized genetic counselling and clinical treatment of affected individuals."
    explanation: The authors name genetic counselling as an application of the molecular diagnosis.
diagnosis:
- name: Molecular Genetic Testing
  description: >-
    Establishes the diagnosis. Probands have been identified by whole-exome
    sequencing, including copy-number analysis of exome data, which detects the
    North African exon 20-21 deletion that sequence-variant calling misses.
  diagnosis_term:
    preferred_term: Genetic Testing
    term:
      id: NCIT:C15709
      label: Genetic Testing
  evidence:
  - reference: PMID:30122540
    reference_title: "A Homozygous Ancestral SVA-Insertion-Mediated Deletion in WDR66 Induces Multiple Morphological Abnormalities of the Sperm Flagellum and Male Infertility."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here, we searched for pathological copy-number variants in whole-exome sequencing data from a cohort of 78 MMAF-affected subjects to identify additional genes associated with MMAF."
    explanation: The founder deletion was found by copy-number analysis of exome data.
  - reference: PMID:41943837
    reference_title: "CFAP251 Deficiency Induces Male Infertility and PCD-like Ciliary Defects by Disrupting TUBB4B and SLC25A4 Recruitment in Humans and Mice."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "CFAP251 mutations were identified by whole-exome sequencing on probands from Han Chinese families with primary infertility and MMAF."
    explanation: Whole-exome sequencing identified the causal alleles.
- name: Semen Analysis
  description: >-
    Shows asthenoteratozoospermia with MMAF, usually with normal sperm
    concentration and absent or very low motility.
  evidence:
  - reference: PMID:41943837
    reference_title: "CFAP251 Deficiency Induces Male Infertility and PCD-like Ciliary Defects by Disrupting TUBB4B and SLC25A4 Recruitment in Humans and Mice."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Routine semen analysis of the two probands revealed severe teratoasthenospermia with complete loss of sperm motility (Table 1)."
    explanation: Semen analysis findings in patients.
- name: Transmission Electron Microscopy of Sperm Flagella
  description: >-
    Shows loss of the central pair and radial spokes with disorganized
    doublets, outer dense fibers, fibrous sheath and mitochondrial sheath.
  diagnosis_term:
    preferred_term: Transmission Electron Microscopy
    term:
      id: NCIT:C18216
      label: Transmission Electron Microscopy
  evidence:
  - reference: PMID:35087568
    reference_title: "Successful Results of Intracytoplasmic Sperm Injection of a Chinese Patient With Multiple Morphological Abnormalities of Sperm Flagella Caused by a Novel Splicing Mutation in CFAP251."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Furthermore, under TEM, for sperm flagella, the cross sections of the patient with the CFAP251 variant displayed typical severe disorganization in axonemal and other periaxonemal structures, in contrast to the “9+2” microtubule structure in normal males."
    explanation: TEM findings in patient sperm.
- name: Immunofluorescence of CFAP251 in Sperm
  description: >-
    Absent CFAP251 staining of sperm flagella supports pathogenicity of
    variants of uncertain significance, such as splice variants.
  evidence:
  - reference: PMID:35087568
    reference_title: "Successful Results of Intracytoplasmic Sperm Injection of a Chinese Patient With Multiple Morphological Abnormalities of Sperm Flagella Caused by a Novel Splicing Mutation in CFAP251."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Simultaneously, western blotting showed the absence of CFAP251 protein translation due to the splicing mutation, and CFAP251 immunostaining was mainly localized at the sperm flagella in normal spermatozoa but was almost absent in the sperm from patients with the CFAP251 variant (Figure 5)."
    explanation: Immunostaining and immunoblotting confirmed loss of function of a splice variant.
📚

References & Deep Research

Deep Research

1

Deep research results are used as seeds for research; they do not undergo the same validation as the main records and may contain errors. How we use deep research.

Evaluations and curation notes (1)

Create: Spermatogenic_Failure_33 · 2026-10-16T13:41:26Z · View source

Created the SPGF33 entry for CFAP251-related male infertility (MONDO:0029147). Sources: a claude_code deep-research report (research/Spermatogenic_Failure_33-deep-research-claude_code.md, preflight PASS) used as leads only, plus PubMed searches for CFAP251/WDR66. Primary evidence: Auguste 2018 and Kherraf 2018 (founder exon 20-21 deletion), Li 2019, Wang 2021 (ICSI pregnancy, maternal UPD), Liu 2026 (splice alleles, knockout mouse, ICSI live births, one patient with cough and CT changes) and a 2026 HOST-ICSI case report, with Tetrahymena CSC structure (Urbanska 2015). Pathograph: Loss of CFAP251 (GO:0005200 DECREASED, radial spoke base 3) -> loss of the calmodulin- and spoke-associated complex (radial spoke assembly DECREASED) -> sperm axonemal disorganization (incl. mitochondrial sheath) -> MMAF -> flagellar phenotypes and male infertility; the CSC nodes use the same names and terms as SPGF51 and SPGF84. A CANONICAL hypothesis records the sperm-restricted phenotype with REFUTE items for the single PCD-like patient and the knockout mouse's tracheal inner dynein arm loss. ClinGen has not classified the pair (2026-10-14 export) and there is no GeneReviews chapter. Validated with just validate, validate-terms, count-verified-snippets (all verified), entity-ref, causal-target, duplicate-key, snippet grading/length/title, reference-title, gene-activity-grounding and GeneReviews checks, and validate-disorders. Stub stubs/Spermatogenic_Failure_33.yaml deleted.

Claude Code ▸
1. Disease Information
claude-haiku-5-5, claude-sonnet-5-5 13 citations 2026-10-16T13:13:42.293470

1. Disease Information

Overview. SPGF33 is an autosomal recessive form of male infertility. It is caused by biallelic loss-of-function variants in CFAP251, formerly called WDR66. The defining finding is multiple morphological abnormalities of the sperm flagella (MMAF), which leave the spermatozoa immotile.

Identifiers - MONDO:0029147 - OMIM 618152 - MedGen C4748395

The identifiers come from MalaCards/LOVD, MedGen and MGI. - I did not verify Orphanet, ICD-10/11 or MeSH identifiers. They are unconfirmed here.

Synonyms: SPGF33; spermatogenic failure, type 33 (SPGF-33).

Gene naming. One search summary flagged a "gene conflict" between WDR66 and CFAP251. This is not a real conflict. They are the same gene under old and new HGNC symbols. Curators must bind by HGNC ID and confirm the current symbol, because the KB checks label and CURIE only for self-consistency.

Data source. The entry is disease-level and aggregated, drawn from case series. It is not derived from EHR data.

Parent term. The disease sits under the broader "spermatogenic failure" concept (MedGen).

2. Etiology

  • Causal factor: biallelic loss of function of CFAP251 (12q24.31).
  • Genetic risk factors: none beyond the recessive causal variants. I found no modifier genes.
  • Environmental risk factors, protective factors and gene-environment interactions: none identified in what I retrieved.

3. Phenotypes

All items are from male patients with MMAF. Frequencies are not quantified in the sources I retrieved.

Phenotype Suggested HPO Notes
Male infertility HP:0003251 Universal
Asthenozoospermia / immotile sperm HP:0012206 (asthenozoospermia), HP:0011961 (? verify) Immotile spermatozoa
Abnormal sperm flagellum morphology (MMAF: short, absent, coiled, bent, irregular-caliber flagella) HP:0012864 (? verify) Defining finding
Abnormal acrosome, head and base none confirmed Reported in the OMIM-derived description

The HPO IDs in this table are unverified suggestions. I did not look any of them up. Per the CLAUDE.md rule, none may be bound until a lookup (OAK or cache/hp/terms.csv) confirms the CURIE and label.

  • Onset: adult presentation, usually when a couple seeks fertility evaluation. This is inferred, not sourced.
  • Quality of life: no data retrieved.
  • Extra-gonadal features: none were reported in the sources I saw. Whether CFAP251 loss affects motile cilia elsewhere in humans is unresolved here. A 2026 paper title suggests ciliary defects in humans and mice (PMID:41943837), but I only saw the title.

4. Genetic / Molecular Information

  • Gene: CFAP251 (WDR66), 12q24.31. HGNC ID not looked up. The KB uses the lowercase hgnc: form.
  • Inheritance: autosomal recessive.
  • Mechanism class: loss of function.

Reported variants

Variant Study Notes
Homozygous deletion of the two penultimate exons, mediated by an SVA retrotransposon insertion Kherraf 2018 (PMID:30122540) 7 of 78 MMAF men; each deletion carried a single chimeric SVA element at the breakpoint, and the authors describe it as "ancestral"
g.122359334delA, p.Asp42Metfs*4 (homozygous) Auguste 2018 (PMID:30122541) Two brothers
g.122359542G>T, p.Glu111* Auguste 2018 Compound heterozygous with the next row
g.122395032_122395033delCT, p.Leu530Valfs*4 Auguste 2018 Compound heterozygous with the previous row
Biallelic loss-of-function variants (specific changes not retrieved) Li 2019 (PMID:30310178) 3 of 65 Han Chinese MMAF men (about 5%)
c.1192-3C>G splicing variant causing exon skipping Wang 2022 (PMID:35087568) The proband inherited it through maternal uniparental disomy
  • Variant origin: germline.
  • Allele frequency: the Li 2019 summary described the variants as extremely rare or absent in population databases. I did not query gnomAD.
  • Chromosomal and epigenetic information: none retrieved.

5. Environmental Information

Not covered. I found no environmental, lifestyle or infectious contributors, and I did not search for them.

6. Mechanism / Pathophysiology

Causal chain

  1. Biallelic loss-of-function variants (SVA-mediated exon deletion, frameshift, nonsense or splice variants) in CFAP251 abolish or truncate the protein. This is demonstrated by genetics. Reduced protein in a patient's sperm was shown by Western blot and immunofluorescence (PMID:35087568).
  2. CFAP251 is an axonemal protein, described in the Auguste title as associated with calmodulin and the radial-spoke complex. Its loss disrupts axoneme assembly or stability in the developing sperm tail. The mechanism here is partly inferred.
  3. Disrupted axoneme assembly produces the MMAF flagellar phenotype: short, absent, coiled and irregular tails.
  4. Transmission electron microscopy suggested that CFAP251 loss affects mitochondrial sheath formation. Auguste's title describes the spermatozoa as "lacking mitochondria", but I only saw a summary. This step is from a small family series.
  5. The abnormal flagella give immotile spermatozoa and male infertility.

Orthologue evidence - Kherraf 2018 localized the Trypanosoma brucei ortholog to the axoneme. Reproducing the human deletion there impaired flagellar movement. This is in vitro/model-organism evidence in a protist. - Auguste 2018 used a Tetrahymena ortholog to show a role in coordinated ciliary beating.

Suggested terms. These are leads only and none has been looked up. - GO terms for axoneme assembly, sperm flagellum assembly and motile cilium assembly. - CL spermatid, plus the UBERON/GO components flagellum and axoneme.

Not covered: omics, single-cell and functional-genomics findings. I did not search for them.

7. Anatomical Structures Affected

  • Primary: testis, with the seminiferous epithelium and the developing spermatid flagellum. The sperm tail and mitochondrial sheath are the structures involved.
  • Localization: bilateral, because the cause is systemic germline. This is inferred.
  • Secondary organs: none documented in the sources I saw. See the caveat on cilia in Section 3.

8. Temporal Development

Adult-onset recognition at fertility evaluation. The condition is non-progressive and lifelong, since it is structural and genetic. Both statements are inferred and not directly sourced.

9. Inheritance and Population

  • Inheritance: autosomal recessive.
  • Prevalence: not retrieved. Penetrance and expressivity are not characterized in what I saw.
  • Frequency among MMAF cohorts: about 9% (7 of 78) in the Kherraf cohort and about 5% (3 of 65) in the Li Han Chinese cohort.
  • Founder effect: Kherraf describes the SVA-mediated deletion as "ancestral". The seven men carried the same deletion type, which is consistent with a founder allele. I did not retrieve population details, so confirm before asserting one. Kherraf's cohort included North African patients. This is from the author list and the Tunisian clinical centres, not from a stated cohort description.
  • Consanguinity: not described in the sources I saw. The Wang 2022 case was nonconsanguineous.
  • Sex ratio: affects males only. Female carriers are presumed unaffected, though I did not verify this.

10. Diagnostics

  • Semen analysis shows immotile spermatozoa and MMAF morphology. Count and morphology details were not retrieved.
  • Genetic testing: whole-exome sequencing identified the variants in all the cited studies. Note that Kherraf's deletion is a structural variant, so copy-number-aware analysis is needed, and a standard SNV/indel pipeline may miss it. This is an inference from the mechanism.
  • Electron microscopy and immunofluorescence can show the axonemal and mitochondrial sheath defects.
  • Differential diagnosis: other MMAF genes such as DNAH1, CFAP43, CFAP44 and CFAP69. These are from general knowledge and were not verified. A review of spermatogenic failure genetics is at PMID:30656449.

11. Outcome / Prognosis

No survival or life-expectancy effect is expected. The disease is confined to fertility, as far as the retrieved sources show. Reproductive prognosis is addressed in Section 12.

12. Treatment

  • No curative treatment is documented.
  • Assisted reproduction: intracytoplasmic sperm injection (ICSI) is the reported route. Wang 2022 reports a successful pregnancy after ICSI in a man with a CFAP251 splice variant (PMID:35087568).
  • A 2026 case report describes sperm selection by hypo-osmotic swelling before ICSI in two men with flagellar defects, one involving CFAP251 (PMID:42871648). I saw only the title.
  • Suggested NCIT term: an assisted-reproduction or ICSI term. None has been looked up. Per the CLAUDE.md rules, search for it and omit the binding if none is suitable.
  • Pharmacotherapy, gene therapy and clinical trials: none found. I did not search ClinicalTrials.gov.
  • The Wang 2022 pregnancy is a single case. Overall ICSI success rates in CFAP251 MMAF are unknown here.

13. Prevention

Not covered, apart from genetic counseling for recurrence risk. The inheritance is autosomal recessive, so a carrier couple has a 25% risk per pregnancy. A male child of two carriers would be affected. I did not search for guidelines.

14. Other Species / Natural Disease

Not covered. I did not check OMIA, so I make no claim about naturally occurring disease in other species.

15. Model Organisms

  • Protists: T. brucei ortholog (axonemal localization, motility impairment with the human deletion) and Tetrahymena ortholog (coordinated ciliary beating). See Section 6.
  • Mouse: I found no mouse knockout data for Cfap251/Wdr66. The searches did not turn up any. A 2026 paper title mentions "humans and mice" (PMID:41943837), which may include a mouse model. Check this paper directly, along with MGI and IMPC.
  • Model limitations: protist models carry the axoneme but not mammalian spermiogenesis or the mitochondrial sheath. This is a likely HUMAN_MODEL_MISMATCH or KNOWLEDGE_GAP candidate until a mouse model is confirmed.

Curation Notes and Open Items

  1. Retracted papers. The WDR66 literature includes cancer papers unrelated to SPGF33. PMID:29717028 is retracted (PMID:36861483) and has an expression of concern (PMID:33870408). Do not cite any of them for this disease.
  2. Verify before binding: all HPO, GO, CL, UBERON and NCIT suggestions above, the HGNC ID for CFAP251, and the Orphanet, ICD and MeSH identifiers.
  3. Exact snippets: none are given. Fetch the references for PMIDs 30122540, 30122541, 30310178 and 35087568, and copy quotes from the cached text.
  4. Evidence source: the case series are HUMAN_CLINICAL. The T. brucei and Tetrahymena results are MODEL_ORGANISM, and the CFAP251 localization is IN_VITRO or MODEL_ORGANISM, depending on how the paper is graded.
  5. Gaps to close: a mouse model, ICSI success rates, the HPO frequency of each phenotype, and the Orphanet and GeneReviews status (use just check-genereviews).

Sources

Reference Validation

Checked with linkml-reference-validator 0.3.0.

Outcome Count
References checked 10
Resolved 10
Unresolved (possible confabulation) 0
Unverifiable 0
References weighed for topical relevance 10
On topic 6
Off topic 0

All extracted references resolved successfully.

Term Validation

Checked with linkml-term-validator 0.4.5, through the ols: adapter.

Outcome Count
Terms checked 6
Resolved 5
Unresolved (possible confabulation) 0
Obsolete 0
Unverifiable 1
Terms whose name was checked 2
Terms named correctly 1
Terms named as a different term 1

Terms the report names something else

These identifiers resolve, so nothing about them looks wrong, and the ontology calls them something unrelated to what the report calls them. That usually means the identifier is not the one the sentence needs:

  • HP:0012864 (1 mention) - the report calls it "? verify"; HP calls it Abnormal sperm morphology

Prefixes with no resolver

Terms carrying these prefixes were not checked either way, because no configured ontology covers them. An unrecognised prefix may name an ontology this run could not reach as easily as one that does not exist, so nothing here is evidence of fabrication: OMIM.