Visceral Heterotaxy 9

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Classifications

Harrison's Part

Mechanistic Nosology

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Mappings

MONDO

MONDO:0030070 heterotaxy, visceral, 9, autosomal, with male infertility

MONDO:0030070 is the primary term for this entry. It carries OMIM:618948 as an xref and records MNS1 (HGNC:29636) as the causal gene via RO:0004003, both of which match the curated content of this entry.

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Inheritance

1

Autosomal recessive HP:0000007

All reported affected individuals carry biallelic MNS1 loss-of-function alleles - homozygous nonsense or frameshift variants in consanguineous and founder pedigrees, and compound heterozygous variants in outbred families. Heterozygous carriers are unaffected. Because left-right axis specification is randomised rather than reversed, sibships homozygous for the same allele segregate a mixture of situs solitus, situs inversus totalis and heterotaxy, so laterality status is not a reliable indicator of genotype within a family.

Autosomal recessive inheritance

Show evidence (2 references)

PMID:30148830 SUPPORT Human Clinical

"we identified two recessive loss-of-function MNS1 mutations in five individuals from four consanguineous families"

Establishes the recessive mode of inheritance in the index cohort of four consanguineous families.

PMID:31534215 SUPPORT Human Clinical

"Genotyping of multiple family members identified randomisation of the laterality defects in other homozygous individuals, with all wild type or MNS1 c.407_410del heterozygous carriers being unaffected, consistent with an autosomal recessive mode of inheritance."

Segregation in an extended Amish pedigree confirms autosomal recessive inheritance with unaffected heterozygous carriers, and documents that laterality is randomised rather than uniformly inverted among homozygotes.

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Discussions and Knowledge Gaps

3

Does biallelic MNS1 loss of function cause primary ciliary dyskinesia-grade airway disease on its own, or only a mild and variable respiratory phenotype that requires a second ciliary lesion to become clinically significant?

KNOWLEDGE GAP OPEN mns1_pcd_boundary

Attached to

pathophysiology#Respiratory Ciliary Dysfunction

The two strongest airway observations in MNS1 deficiency are confounded or isolated. In the index cohort, the one individual with recurrent respiratory infections and the informative distal ODA-docking ultrastructure also carried homozygous DNAH5 mutations, a well-established PCD gene, so her airway phenotype cannot be attributed to MNS1 alone. The later report of a pronounced respiratory phenotype rests on a single six-year-old girl, with two further individuals showing only a mild phenotype. ClinGen's Motile Ciliopathy Gene Curation Expert Panel classifies the MNS1-primary ciliary dyskinesia gene-disease relationship as Disputed. Resolving this matters clinically: it determines whether MNS1-deficient individuals need PCD surveillance (airway clearance, spirometry, imaging for bronchiectasis) or only laterality and fertility management.

Proposed experiments

Systematic PCD diagnostic workup of an MNS1 cohort

mns1_pcd_diagnostic_battery

Apply the standard PCD diagnostic battery - nasal nitric oxide, high-speed video microscopy of ciliary beat frequency and waveform, transmission electron microscopy and air-liquid interface culture - to every reported MNS1-deficient individual without a second motile-ciliopathy gene lesion, and compare against genotype-matched DNAH5 controls. Only a systematic, second-gene-negative series can separate an MNS1-intrinsic airway phenotype from digenic or coincidental disease.

Decision criterion

MNS1 is judged an independent cause of PCD-grade airway disease if second-gene-negative individuals show low nasal nitric oxide together with abnormal ciliary beat pattern in the majority of cases; it is judged insufficient alone if those individuals are indistinguishable from controls.

Would support

pathophysiology#Respiratory Ciliary Dysfunction

Show evidence (2 references)

PMID:30148830 SUPPORT Human Clinical

"a homozygous nonsense mutation p.Gln203* in one female with laterality defects and recurrent respiratory infections additionally carrying homozygous mutations in DNAH5"

Documents the DNAH5 co-mutation that confounds attribution of the airway phenotype to MNS1 in the index cohort.

CGGV:assertion_255ba802-ece2-43c7-9089-6e54672b4f4a-2022-09-13T170000.000Z SUPPORT Other

An expert panel's formal classification of the MNS1-PCD relationship as Disputed, the current authoritative statement of this gap.

Mns1-null mice develop hydrocephalus, a canonical consequence of ependymal motile cilia dysfunction, yet hydrocephalus has not been reported in any MNS1-deficient human. Is the ependymal arm of MNS1 function genuinely absent in humans, or has it simply not been looked for?

HUMAN MODEL MISMATCH OPEN mns1_hydrocephalus_model_mismatch

Attached to

pathophysiology#Nodal Cilia Motility Failure at the Left-Right Organizer

Ependymal cilia use the same axonemal machinery as nodal and respiratory cilia, so an MNS1-dependent ependymal phenotype is mechanistically expected. Its absence from the human literature could reflect a true species difference (mouse aqueductal geometry makes murine hydrocephalus far more sensitive to ciliary dysfunction than the human equivalent), ascertainment bias (affected individuals are ascertained through cardiology and fertility clinics, not neurology, and brain imaging is not routinely reported), or the small size of the published cohort. This is a model-fidelity question rather than a plain absence of evidence: the evidence exists in mouse and its translational validity to human disease is what is uncertain.

Proposed experiments

Prospective neuroimaging of MNS1-deficient individuals

mns1_prospective_neuroimaging

Obtain brain MRI with ventricular volumetry in every genetically confirmed MNS1-deficient individual, and report ependymal ciliary function where post-mortem or surgical tissue is available. This distinguishes a genuine species difference from a reporting gap; a negative imaging series across the known cohort would itself be a substantive human result.

Decision criterion

Ventriculomegaly in a meaningful fraction of the imaged cohort would establish the ependymal arm in humans; normal ventricular volumes across the full known cohort would establish the mouse hydrocephalus phenotype as species-specific.

Show evidence (2 references)

PMID:22396656 SUPPORT Model Organism

"In addition, MNS1-deficient mice display situs inversus and hydrocephalus."

The mouse phenotype that has no reported human counterpart.

PMID:38920647 SUPPORT Human Clinical

"Defects in motile cilia, termed motile ciliopathies, result in clinical manifestations affecting the respiratory and reproductive system, as well as laterality defects and hydrocephalus."

Hydrocephalus is listed among the expected manifestations of motile ciliopathies in general, yet is not among the findings reported in this paper's five MNS1-deficient individuals.

Are the non-ciliary features reported in individual MNS1 cases - severe myopia and oligodontia in one compound heterozygous woman, and a complex prenatal malformation syndrome in a sibling fetal pair - part of the MNS1 phenotype, or attributable to coincidental or second-locus variation?

KNOWLEDGE GAP OPEN mns1_phenotype_expansion_uncertainty

Attached to

pathophysiology#Randomization of Left-Right Axis Specification

The report expanding the MNS1 phenotype describes features with no known connection to motile cilia. Critically, the two affected fetuses in that report carried homozygous GLDN variants in addition to their in-frame MNS1 deletion, so their malformation syndrome cannot be attributed to MNS1 without disentangling the two loci. Given that only a handful of individuals have ever been reported, single additional features carry disproportionate weight in shaping the perceived phenotype, and this entry deliberately does not curate them as MNS1 phenotypes.

Show evidence (2 references)

PMID:39233552 SUPPORT Human Clinical

"The second and third patients were sibling fetuses with homozygous in-frame deletion variants in MNS1 and homozygous missense variants in GLDN."

Documents the second-locus variant that confounds attribution of the fetal malformation syndrome to MNS1.

PMID:39233552 SUPPORT Human Clinical

"The first patient was a female presenting complete situs inversus and unusual symptoms, including severe myopia and dental agenesis of 10 permanent teeth."

The authors themselves describe these features as unusual, marking them as unresolved rather than established components of the phenotype.

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Pathophysiology

7

Biallelic MNS1 Loss of Function

Homozygous or compound heterozygous nonsense, frameshift and in-frame deletion alleles in MNS1 abolish production of functional MNS1 protein. Immunofluorescence in affected individuals shows loss of MNS1 from the axonemes and flagella where the wild-type protein normally resides, confirming that the reported alleles behave as true nulls at the protein level rather than as hypomorphs of uncertain consequence.

MNS1 hgnc:29636

Downstream

Outer Dynein Arm Docking Defect in the Motile Axoneme Absence of the MNS1 protein removes a structural component required for normal assembly and docking of outer dynein arms on the axonemal outer doublet microtubules.

Show evidence (2 references)

PMID:30148830 SUPPORT Human Clinical

"Immunofluorescence analysis further revealed that MNS1 localizes to the axonemes of respiratory cilia as well as sperm flagella in human."

Establishes where wild-type MNS1 protein resides in human tissue, the baseline against which its loss in patients is scored.

PMID:33037173 SUPPORT Human Clinical

"Immunostaining analysis showed MNS1 to be normally located in the whole-sperm flagella, but was absent in the proband's sperm."

Demonstrates at the protein level that a frameshift allele results in absent MNS1 from the flagellum.

Outer Dynein Arm Docking Defect in the Motile Axoneme

MNS1 dimerises and binds CCDC114, a component of the outer dynein arm docking complex (ODA-DC). Without MNS1, outer dynein arms are incompletely docked onto the outer doublet microtubules. Crucially, the resulting ultrastructural lesion is subtle - a partial rather than complete loss of outer dynein arms, most pronounced in the distal axoneme - which distinguishes MNS1 deficiency from the complete ODA loss seen with DNAH5 or DNAI1 defects and accounts for the mild airway phenotype relative to classic primary ciliary dyskinesia.

outer dynein arm assembly GO:0036158 ↓ DECREASED

axoneme GO:0005930

Downstream

Nodal Cilia Motility Failure at the Left-Right Organizer The motile monocilia of the embryonic left-right organiser depend on outer dynein arm-driven beating to generate leftward nodal flow.

Sperm Flagellar Axoneme Assembly Failure The sperm flagellum is built on the same 9+2 axonemal template and requires MNS1 as an integral structural component.

Respiratory Ciliary Dysfunction Partial outer dynein arm loss in airway multiciliated cells impairs mucociliary clearance in a subset of affected individuals.

Partial absence of outer dynein arms in respiratory cilia The docking defect is what transmission electron microscopy of patient respiratory cilia visualises as partial outer dynein arm loss.

Show evidence (2 references)

PMID:30148830 SUPPORT Human Clinical

"In-depth ultrastructural analyses confirmed a subtle outer dynein arm (ODA) defect in the axonemes of respiratory epithelial cells resembling findings reported in Mns1-deficient mice."

Documents the ultrastructural lesion in patient respiratory axonemes and explicitly characterises it as subtle.

PMID:30148830 SUPPORT Human Clinical

"Ultrastructural analyses in the female carrying combined mutations in MNS1 and DNAH5 indicated a role for MNS1 in the process of ODA docking (ODA-DC) in the distal respiratory axonemes."

Localises the MNS1-dependent docking defect to the distal respiratory axoneme.

Nodal Cilia Motility Failure at the Left-Right Organizer

During gastrulation, motile monocilia at the ventral node beat to drive a leftward extraembryonic fluid flow that is the earliest known symmetry-breaking event in the vertebrate embryo. MNS1 is expressed in the mouse ventral node, and MNS1 deficiency compromises the outer dynein arm machinery that powers this beat, so nodal flow fails to be established robustly.

ciliated epithelial cell CL:0000067

cilium movement GO:0003341 ↓ DECREASED determination of left/right symmetry GO:0007368 ⚠ ABNORMAL

Animal models

Mns1 knockout mouse Mouse recapitulates Mns1-null mice display situs inversus, the organismal readout of failed nodal cilium function, and their tracheal motile cilia show the partial outer dynein arm loss that is the presumed proximate cause.

Downstream

Randomization of Left-Right Axis Specification Absent or insufficient nodal flow leaves the left-right axis unspecified, so situs is determined stochastically in each embryo.

Show evidence (2 references)

PMID:30148830 SUPPORT Model Organism

"Consistent with the laterality defects observed in these individuals, we found Mns1 to be expressed in mouse embryonic ventral node."

Expression at the left-right organiser is the evidence that MNS1 acts at this node of the mechanism.

PMID:31534215 SUPPORT Human Clinical

"This study identifies an MNS1 variant as a cause of laterality defects and male infertility in humans, mirroring findings in Mns1-deficient mice which also display male infertility and randomisation of left-right asymmetry of internal organs, confirming a crucial role for MNS1 in nodal cilia and..."

Explicitly assigns MNS1 a crucial role in nodal cilia formation and function, the conformance claim of this node.

Respiratory Ciliary Dysfunction

MNS1 is present in the axonemes of human respiratory cilia, and affected individuals show its absence from airway epithelium together with a partial outer dynein arm defect. Unlike classic primary ciliary dyskinesia, however, the airway consequence is variable and frequently absent: most reported individuals have no significant otosinopulmonary disease, and the airway arm of the module is only partially manifested. Where it does occur it presents as neonatal respiratory distress, recurrent respiratory tract infection, chronic rhinitis and wet cough rather than established bronchiectasis.

multiciliated airway epithelial cell CL:0002145

epithelial cilium movement involved in extracellular fluid movement GO:0003351 ↓ DECREASED

respiratory airway UBERON:0001005

Downstream

Recurrent respiratory tract infections Impaired mucociliary clearance predisposes to recurrent lower and upper airway infection in the minority of individuals with an airway phenotype.

Chronic rhinitis Upper-airway manifestation of impaired mucociliary clearance.

Neonatal respiratory distress Failure of perinatal airway clearance, the earliest airway manifestation of motile ciliary dysfunction.

Recurrent otitis media Middle-ear clearance depends on the same motile cilia, so otitis media is the mildest and most frequently isolated airway manifestation.

Show evidence (2 references)

PMID:38920647 SUPPORT Human Clinical

"This study represents the first observation of heterotaxia and respiratory disease in individuals with biallelic MNS1 variants, an important extension of the phenotype associated with MNS1-related motile ciliopathy disorder."

Establishes that respiratory disease is part of the MNS1 phenotype, while its framing as a novel extension records that it is not the usual presentation.

PMID:38920647 SUPPORT Human Clinical

"Two other individuals with hypomorphic variants showed laterality defects and mild respiratory phenotype."

Records that where airway involvement occurs in MNS1 deficiency it is typically mild, which is the qualification this node carries relative to the module's airway arm.

Sperm Flagellar Axoneme Assembly Failure

MNS1 is an integral, detergent-resistant component of the sperm flagellum. In its absence the flagellar axoneme is not correctly assembled: the 9+2 microtubule arrangement and the surrounding outer dense fibres are disrupted, and outer doublet microtubules show ultrastructural disturbance in human patients. Because MNS1 loss acts during spermiogenesis - the post-meiotic morphogenesis of the round spermatid into a spermatozoon - both the number and the structure of the resulting gametes are affected.

sperm CL:0000019

sperm axoneme assembly GO:0007288 ↓ DECREASED spermatid development GO:0007286 ⚠ ABNORMAL

Animal models

Mns1 knockout mouse Mouse recapitulates The mouse null reproduces the human flagellar assembly defect at both the light-microscopic (short, immotile tails) and ultrastructural (disrupted 9+2 axoneme and outer dense fibres) level.

Downstream

Oligoasthenoteratozoospermia and Male Infertility Failure of flagellar assembly during spermiogenesis yields few, malformed and immotile spermatozoa.

Show evidence (4 references)

PMID:33037173 SUPPORT Human Clinical

"Abnormal flagellum morphology and ultrastructural disturbances in outer doublet microtubules were observed in the proband's sperm."

Human ultrastructural evidence that MNS1 loss disrupts flagellar axoneme architecture.

PMID:33037173 SUPPORT Human Clinical

"In our study, MNS1 defect was associated with missing peripheral DMTs (2–4 out of 9) and absent ODAs in humans"

Ties the sperm flagellar defect specifically to loss of outer dynein arms, which is the same lesion the upstream Outer Dynein Arm Docking Defect node describes. This is what makes the axoneme node a continuation of the ODA docking defect in sperm rather than an independent spermatogenic failure.

PMID:22396656 SUPPORT Model Organism

"We find that MNS1 is expressed in the germ cells in the testes and localizes to sperm flagella in a detergent-resistant manner, indicating that it is an integral component of flagella."

Establishes MNS1 as a structural component of the flagellum rather than a transient assembly factor.

+ 1 more reference

Randomization of Left-Right Axis Specification

With nodal flow absent, left-right identity is assigned stochastically rather than deterministically. Some affected individuals develop normal situs solitus, some develop mirror-image situs inversus totalis, and a further fraction fails to establish a coherent axis at all and develops true heterotaxy (situs ambiguus) with discordant thoracic and abdominal arrangement and complex congenital heart disease. This randomisation - as opposed to consistent reversal - is the signature of a nodal-cilium laterality defect and explains the intrafamilial variability seen in MNS1 pedigrees.

determination of left/right symmetry GO:0007368 ⚠ ABNORMAL

Downstream

Laterality defect Abnormal left-right arrangement of the thoraco-abdominal organs is the direct clinical expression of a randomised left-right axis.

Situs inversus totalis Complete mirror-image reversal is the outcome when a coherent but inverted axis is established.

Complex congenital heart disease When no coherent axis is established, cardiac segments are discordantly arranged and complex structural heart disease results.

Asplenia Splenic agenesis accompanies right isomerism, the bilateral-right-sidedness form of a failed left-right axis.

Show evidence (2 references)

PMID:31534215 SUPPORT Human Clinical

"Genotyping of multiple family members identified randomisation of the laterality defects in other homozygous individuals, with all wild type or MNS1 c.407_410del heterozygous carriers being unaffected, consistent with an autosomal recessive mode of inheritance."

Documents randomisation, rather than uniform inversion, of laterality among homozygotes in a single extended pedigree.

PMID:38920647 SUPPORT Human Clinical

"A broad spectrum of laterality defects including situs inversus totalis and heterotaxia was confirmed."

Confirms that the laterality outcome spans complete mirror-imaging through to true heterotaxy.

Oligoasthenoteratozoospermia and Male Infertility

Affected males have severe oligoasthenoteratozoospermia: reduced sperm counts, absent or near-absent progressive motility, and abnormal head and tail morphology. Infertility is the consistent reproductive outcome. In the one reported attempt, intracytoplasmic sperm injection did not rescue fertility, which is consistent with the defect being structural and gamete-intrinsic rather than purely motility-limited.

Downstream

Male infertility The reproductive endpoint of the flagellar defect in affected males.

Reduced sperm motility Immotility is the functional component of the oligoasthenoteratozoospermia triad.

Oligozoospermia The quantitative component of the oligoasthenoteratozoospermia triad.

Abnormal sperm morphology The structural component of the oligoasthenoteratozoospermia triad.

Show evidence (2 references)

PMID:33037173 SUPPORT Human Clinical

"The semen examination results of the proband were as follows: semen volume, 3.4 ml; sperm concentration, 1.8 × 106 ml−1; and percentage progressive motility, 5.8%."

The measured semen phenotype of the MNS1-deficient proband. All three components of the oligoasthenoteratozoospermia triad are quantified in the same individual and each falls below the WHO lower reference limit, which is what makes this node an observed outcome rather than a definitional label.

PMID:30148830 SUPPORT Human Clinical

"a homozygous nonsense mutation p.Arg242* in four males with laterality defects and infertility"

Reports infertility in all four homozygous males in the index cohort. Recorded as PARTIAL because the same paper qualifies the association as likely male infertility, formal semen analysis not being available for every individual.

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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

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Phenotypes

13

Cardiovascular 2

Situs inversus totalis HP:0001696

Show evidence (2 references)

PMID:31534215 SUPPORT Human Clinical

"we investigated the genetic cause of a form of situs inversus (SI) and male infertility present in multiple individuals in an extended Amish family"

Situs inversus was the ascertaining phenotype in this pedigree.

PMID:39233552 SUPPORT Human Clinical

"The first patient was a female presenting complete situs inversus and unusual symptoms, including severe myopia and dental agenesis of 10 permanent teeth."

Independent report of complete situs inversus in a compound heterozygous individual.

Complex congenital heart disease Abnormal heart morphology HP:0001627

HP:0001627 (Abnormal heart morphology) is used because HPO has no single term for complex congenital heart disease; the preferred_term carries the intended clinical granularity.

Show evidence (1 reference)

PMID:38920647 SUPPORT Human Clinical

"All four affected individuals presented with laterality defects, including one male individual with heterotaxia and complex congenital heart defects."

Reports complex congenital heart defects in the individual with true heterotaxy.

Ear 1

Recurrent otitis media OCCASIONAL HP:0000403

Show evidence (1 reference)

PMID:31534215 SUPPORT Human Clinical

"All affected individuals were clinically assessed, no PCD symptoms were reported, with the exception of IX-1 who suffered recurrent otitis media."

IX-1 was the only individual in this pedigree with any airway symptom; every other assessed homozygote was explicitly free of PCD symptoms. Against the six homozygotes the same paper reports, that is 1/6 (17%), inside the occasional (5-29%) band.

Genitourinary 1

Male infertility HP:0003251

Show evidence (2 references)

PMID:31534215 SUPPORT Human Clinical

"This study identifies an MNS1 variant as a cause of laterality defects and male infertility in humans, mirroring findings in Mns1-deficient mice which also display male infertility and randomisation of left-right asymmetry of internal organs, confirming a crucial role for MNS1 in nodal cilia and..."

States male infertility as an established consequence of the MNS1 variant in humans.

PMID:33037173 SUPPORT Human Clinical

"A total of three intracytoplasmic sperm injection cycles were carried out for the proband's wife, but they all failed to lead to a successful pregnancy."

Documents failure of assisted reproduction, the practical severity of the infertility phenotype.

Immune 1

Recurrent respiratory tract infections OCCASIONAL Recurrent respiratory infections HP:0002205

Show evidence (1 reference)

PMID:38920647 SUPPORT Human Clinical

"Interestingly, a single affected six-year-old girl homozygous for an MNS1 nonsense variant presented with a history of neonatal respiratory distress syndrome, recurrent respiratory tract infections, chronic rhinitis, and wet cough."

One of five newly reported individuals, framed by the authors as noteworthy precisely because it is unusual, had a pronounced respiratory phenotype; combined with the two further individuals reported to have only a mild respiratory phenotype this supports an occasional (5-29%) band for clinically significant recurrent infection.

Respiratory 1

Neonatal respiratory distress HP:0002643

Show evidence (1 reference)

PMID:38920647 SUPPORT Human Clinical

"Interestingly, a single affected six-year-old girl homozygous for an MNS1 nonsense variant presented with a history of neonatal respiratory distress syndrome, recurrent respiratory tract infections, chronic rhinitis, and wet cough."

Neonatal respiratory distress syndrome is explicitly reported.

Other 7

Laterality defect FREQUENT Heterotaxy HP:0030853

Show evidence (3 references)

PMID:38920647 SUPPORT Human Clinical

"A broad spectrum of laterality defects including situs inversus totalis and heterotaxia was confirmed."

Confirms laterality defects, including frank heterotaxy, across the reported cohort.

PMID:30148830 SUPPORT Human Clinical

"a homozygous nonsense mutation p.Arg242* in four males with laterality defects and infertility"

Establishes the association: all five reported homozygotes across four consanguineous families had laterality defects. These individuals were ascertained through those defects, so the count fixes the disease-phenotype association but cannot estimate its frequency; the band is carried by the genotype-first pedigree count below.

PMID:31534215 SUPPORT Human Clinical

"Six individuals were found to be homozygous for the MNS1 NM_018365.2:c.407_410del variant, of whom four (67%) exhibited SI and two (33%) exhibited situs solitus."

The one genotype-first denominator available for this disorder: 26 members of the Amish pedigree were genotyped and clinically assessed, and four of the six homozygotes so identified (67%) had a laterality defect while two had normal situs. 67% sits in the frequent (30-79%) band. The two situs solitus homozygotes are what the randomisation mechanism predicts, and are why a very frequent (80-99%) band would contradict this entry's central claim.

Asplenia HP:0001746

Show evidence (1 reference)

PMID:38920647 SUPPORT Human Clinical

"Individual EX-1II1 presented with right isomerism, asplenia, and complex congenital heart disease that required surgical intervention."

Reports asplenia in an MNS1-deficient individual, together with the right isomerism that mechanistically explains it.

Reduced sperm motility HP:0012207

Show evidence (2 references)

PMID:33037173 SUPPORT Human Clinical

"The semen examination results of the proband were as follows: semen volume, 3.4 ml; sperm concentration, 1.8 × 106 ml−1; and percentage progressive motility, 5.8%."

Progressive motility measured at 5.8% in the MNS1-deficient proband, far below the WHO lower reference limit. A measured value in a named individual rather than a definition of the term.

PMID:22396656 SUPPORT Model Organism

"MNS1-deficient males are sterile, as they exhibit a sharp reduction in sperm production and the remnant sperm are immotile with abnormal short tails."

Mouse null spermatozoa are immotile. Kept as MODEL_ORGANISM alongside the human oligoasthenoteratozoospermia report rather than substituting for it.

Oligozoospermia HP:0000798

Show evidence (1 reference)

PMID:33037173 SUPPORT Human Clinical

"The semen examination results of the proband were as follows: semen volume, 3.4 ml; sperm concentration, 1.8 × 106 ml−1; and percentage progressive motility, 5.8%."

Sperm concentration measured at 1.8 million per ml in the MNS1-deficient proband, an order of magnitude below the WHO lower reference limit.

Abnormal sperm morphology HP:0012864

Show evidence (1 reference)

PMID:33037173 SUPPORT Human Clinical

"Abnormal flagellum morphology and ultrastructural disturbances in outer doublet microtubules were observed in the proband's sperm."

Direct morphological and ultrastructural description of the patient's spermatozoa.

Chronic rhinitis HP:0002257

Show evidence (1 reference)

PMID:38920647 SUPPORT Human Clinical

"Interestingly, a single affected six-year-old girl homozygous for an MNS1 nonsense variant presented with a history of neonatal respiratory distress syndrome, recurrent respiratory tract infections, chronic rhinitis, and wet cough."

Chronic rhinitis is explicitly enumerated in the respiratory presentation.

Partial absence of outer dynein arms in respiratory cilia Absent outer dynein arms HP:0012256

Show evidence (1 reference)

PMID:30148830 SUPPORT Human Clinical

"In-depth ultrastructural analyses confirmed a subtle outer dynein arm (ODA) defect in the axonemes of respiratory epithelial cells resembling findings reported in Mns1-deficient mice."

Recorded as PARTIAL because the defect described is subtle and partial, whereas HP:0012256 (Absent outer dynein arms) names complete absence; the HPO term is the closest available and the preferred_term and description carry the qualification.

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Genetic Associations

1

MNS1

Gene: MNS1 hgnc:29636 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (4 references)

PMID:30148830 SUPPORT Human Clinical

"we demonstrate that MNS1 deficiency in humans causes laterality defects (situs inversus) and likely male infertility and that MNS1 plays a role in the ODA-DC assembly"

Names MNS1 as the causal gene for this disease and states its molecular role in outer dynein arm docking complex assembly.

PMID:30148830 SUPPORT In Vitro

"co-immunoprecipitation and yeast two hybrid analyses demonstrated that MNS1 dimerizes and interacts with the ODA docking complex component CCDC114"

Biochemical interaction data establishing the molecular function of the MNS1 protein product.

PMID:39233552 SUPPORT Human Clinical

"MNS1 (meiosis-specific nuclear structural protein-1 gene) encodes a structural protein implicated in motile ciliary function and sperm flagella assembly."

Independent statement of the gene product's function in motile cilia and sperm flagella.

+ 1 more reference

Variants (3)

MNS1 p.Arg242*

Homozygous nonsense variant identified in four males with laterality defects and infertility from consanguineous families; the index allele for HTX9.

Show evidence (1 reference)

PMID:30148830 SUPPORT Human Clinical

"a homozygous nonsense mutation p.Arg242* in four males with laterality defects and infertility"

Directly reports the variant, its zygosity, and the associated phenotype.

MNS1 c.407_410del p.(Glu136Glyfs*16)

Homozygous founder frameshift allele segregating in an extended Amish pedigree with situs inversus and male infertility.

Show evidence (1 reference)

PMID:31534215 SUPPORT Human Clinical

"we investigated the genetic cause of a form of situs inversus (SI) and male infertility present in multiple individuals in an extended Amish family"

Establishes the pedigree and phenotype in which this founder frameshift allele was identified.

MNS1 c.603_604insG p.Lys202Glufs*6

Homozygous frameshift variant identified in a Han Chinese proband with severe oligoasthenoteratozoospermia, the fertility-only presentation of MNS1 deficiency.

Show evidence (1 reference)

PMID:33037173 SUPPORT Human Clinical

"we identified a novel homozygous frameshift mutation in meiosis-specific nuclear structural 1 (MNS1; NM_018365: c.603_604insG: p.Lys202Glufs*6) by whole-exome sequencing in an OAT proband from a consanguineous Chinese family"

Reports the variant and the isolated infertility phenotype in which it was ascertained.

💊

Medical Actions

2

Surgical management of congenital heart disease

Action: surgical procedure Ontology label: Surgical Procedure NCIT:C15329

In individuals with true heterotaxy and complex congenital heart disease, staged cardiac surgical repair or palliation is the mainstay of management. There is no MNS1-directed or mechanism-targeted therapy; management is entirely supportive and directed at the individual anatomical and functional consequences of the laterality defect.

Target Phenotypes: Complex congenital heart malformation HP:0001627

Assisted reproduction (intracytoplasmic sperm injection)

Action: intracytoplasmic sperm injection Ontology label: Intracytoplasmic Sperm Injection NCIT:C185482

ICSI is the conventional approach to severe oligoasthenoteratozoospermia. In the single reported MNS1-deficient couple, three ICSI cycles all failed to achieve pregnancy, so ICSI should not be presented to affected men as reliably effective.

Mechanism Target:

BYPASSES Oligoasthenoteratozoospermia and Male Infertility — ICSI does not correct the flagellar lesion. It circumvents the requirement for sperm motility and normal morphology by injecting a single spermatozoon directly into the oocyte, so it acts on the reproductive consequence rather than on any upstream mechanism node. In the one reported MNS1-deficient couple the bypass worked as far as fertilisation and cleavage but did not produce a pregnancy, so it is recorded as an incomplete bypass.

Show evidence (1 reference)

PMID:33037173 SUPPORT Human Clinical

"eight eggs were fertilized successfully (fertilization rate: 80%), and eight viable cleavage embryos were achieved, which suggests that normal embryos could be obtained using the spermatozoa with the MNS1 mutation during ICSI treatment"

Direct evidence that the gamete-intrinsic defect can be bypassed at fertilisation. Recorded as PARTIAL because the same cycle did not lead to pregnancy, so the bypass is demonstrated only up to the cleavage stage.

Target Phenotypes: Male infertility HP:0003251

Show evidence (1 reference)

PMID:33037173 REFUTE Human Clinical

"A total of three intracytoplasmic sperm injection cycles were carried out for the proband's wife, but they all failed to lead to a successful pregnancy."

A negative therapeutic result: three ICSI cycles in the only reported MNS1-deficient couple did not achieve pregnancy. Recorded as REFUTE against the implicit claim that ICSI reliably rescues fertility in this disorder. This is a single couple, so it constrains rather than settles the question.

🔬

Diagnosis

2

Molecular genetic testing

Diagnosis rests on identification of biallelic loss-of-function MNS1 variants by exome, genome or motile-ciliopathy panel sequencing in an individual with a laterality defect, with or without male infertility. Because the airway phenotype is usually absent, MNS1 deficiency is frequently reached through genome-wide sequencing of a heterotaxy cohort rather than through a primary ciliary dyskinesia diagnostic pathway.

Show evidence (1 reference)

PMID:39513328 SUPPORT Human Clinical

"Our work demonstrates a relatively high yield of genetic testing in HTX in a consanguineous population with an enrichment of homozygous variants."

Supports genome-wide molecular testing as the diagnostic route by which recessive heterotaxy genes including MNS1 are identified.

Immunofluorescence analysis of ciliated cells

Immunofluorescence staining of respiratory epithelial cells or spermatozoa demonstrates absence of MNS1 from the axoneme, and is used to confirm the functional consequence of candidate variants.

Show evidence (1 reference)

PMID:38920647 SUPPORT Human Clinical

"Accordingly, immunofluorescence analysis showed the absence of MNS1 from the respiratory epithelial cells of this individual."

Demonstrates the use of immunofluorescence to confirm loss of the MNS1 protein in a patient sample.

📊

Prevalence

2

Worldwide

Cases In Literature Ultra Rare

Fewer than twenty affected individuals have been reported since the disease was delineated in 2018: five in the index cohort of four consanguineous families, an extended Amish founder pedigree, five individuals from four further families, three individuals in a French/GeneMatcher report, one Han Chinese proband ascertained through infertility, and single cases in heterotaxy cohort studies. No population prevalence estimate exists.

Show evidence (2 references)

PMID:39233552 SUPPORT Human Clinical

"We add here new cases with the ultra-rare MNS1-related disorder and provide a review of all published individuals."

The most recent review of all published individuals characterises the disorder as ultra-rare.

PMID:39233552 SUPPORT Human Clinical

"To date, two different homozygous MNS1 variants have been associated with autosomal recessive visceral heterotaxy"

Quantifies how small the reported allelic series was at the time of the most recent review.

Consanguineous heterotaxy cohort, Saudi Arabia

Cases In Literature Unknown

MNS1 was one of eight autosomal recessive heterotaxy genes identified in a consecutively recruited consanguineous cohort of 24 affected individuals from 19 families, illustrating that MNS1 is a recurring but individually minor contributor to the genetic architecture of heterotaxy.

Show evidence (1 reference)

PMID:39513328 SUPPORT Human Clinical

"Genetic analysis, with exome sequencing, genome sequencing, or multigene panel, detected 9 unique variants, 7 of which were novel, in 8 genes known to be implicated in autosomal recessive form of HTX (C1orf127, CCDC39, CIROP, DNAAF3, DNAH5, DNAH9, MMP21, and MNS1) providing a yield of 42.1%."

Places MNS1 among the recurrently implicated autosomal recessive heterotaxy genes in a consanguineous population.

🐁

Animal Models

1

Mns1 knockout mouse

The founding loss-of-function model for MNS1 deficiency. Mns1-null males are sterile with markedly reduced sperm production and immotile, short-tailed spermatozoa in which the 9+2 microtubule arrangement and outer dense fibres are disrupted. The mice also display situs inversus and hydrocephalus, and their tracheal motile cilia lack a subset of outer dynein arms - the same partial ODA lesion later found in human patients.

Species

Mouse

Genotype

Mns1 null (homozygous)

Publication

PMID:22396656

Pathograph links

Sperm Flagellar Axoneme Assembly Failure recapitulates fidelity: high The mouse null reproduces the human flagellar assembly defect at both the light-microscopic (short, immotile tails) and ultrastructural (disrupted 9+2 axoneme and outer dense fibres) level.

Limitations: Mouse sterility is complete, whereas the human phenotype is reported as severe oligoasthenoteratozoospermia with residual sperm production; the human quantitative severity is therefore not identical.

Readouts

Sperm production and flagellar ultrastructure

Direction: DECREASED

Interpretation: Reduced sperm output with disrupted axonemal and outer dense fibre architecture is the structural correlate of the flagellar assembly node.

Show evidence (1 reference)

PMID:22396656 SUPPORT Model Organism

"MNS1-deficient males are sterile, as they exhibit a sharp reduction in sperm production and the remnant sperm are immotile with abnormal short tails."

Reports the measured reduction in sperm production and the flagellar abnormality.

Show evidence (1 reference)

PMID:22396656 SUPPORT Model Organism

"These results demonstrate that MNS1 is essential for spermiogenesis, the assembly of sperm flagella, and motile ciliary functions."

Establishes the model as informative for the flagellar assembly mechanism.

Nodal Cilia Motility Failure at the Left-Right Organizer recapitulates fidelity: moderate Mns1-null mice display situs inversus, the organismal readout of failed nodal cilium function, and their tracheal motile cilia show the partial outer dynein arm loss that is the presumed proximate cause.

Limitations: Nodal cilium beating and nodal flow were not measured directly in this study; situs inversus and tracheal ciliary ultrastructure are used as proxies. The mouse also develops hydrocephalus, which has not been reported in MNS1-deficient humans.

Readouts

Tracheal ciliary outer dynein arm content

Direction: DECREASED

Interpretation: Partial loss of outer dynein arms from motile cilia is the ultrastructural readout supporting impaired ciliary beating in this model.

Show evidence (1 reference)

PMID:22396656 SUPPORT Model Organism

"MNS1-deficient tracheal motile cilia lack some outer dynein arms in the axoneme."

Reports the measured ultrastructural deficit, and notably that it is partial, matching the human finding.

Show evidence (1 reference)

PMID:22396656 SUPPORT Model Organism

"In addition, MNS1-deficient mice display situs inversus and hydrocephalus."

The laterality phenotype in the mouse null is the organismal evidence that this model is informative for the nodal-cilium node.

Show evidence (1 reference)

PMID:22396656 SUPPORT Model Organism

"Here, we report that MNS1, a coiled-coil protein of unknown function, is essential for spermiogenesis."

Establishes the Mns1-null mouse as a characterised loss-of-function model of the gene curated here.

{ }

Source YAML

click to show

name: Visceral Heterotaxy 9
creation_date: "2026-08-18T00:00:00Z"
category: Mendelian
disease_term:
  preferred_term: heterotaxy, visceral, 9, autosomal, with male infertility
  term:
    id: MONDO:0030070
    label: heterotaxy, visceral, 9, autosomal, with male infertility
synonyms:
- HTX9
- heterotaxy, visceral, 9, autosomal, with male infertility
- MNS1-related motile ciliopathy
- MNS1-related laterality defect with male infertility
description: >-
  Visceral heterotaxy 9 (HTX9) is an ultra-rare autosomal recessive motile
  ciliopathy caused by biallelic loss-of-function variants in MNS1
  (meiosis-specific nuclear structural protein 1). MNS1 is an integral
  coiled-coil component of the motile axoneme that dimerises and binds the outer
  dynein arm docking complex subunit CCDC114; its loss produces a subtle outer
  dynein arm and ODA-docking defect rather than the gross axonemal disorganisation
  of classic primary ciliary dyskinesia. Because the same axonemal machinery
  powers the motile monocilia of the embryonic left-right organiser and the sperm
  flagellum, MNS1 deficiency produces a characteristic two-part phenotype:
  randomisation of left-right body asymmetry (situs inversus totalis or true
  heterotaxy, with complex congenital heart disease in a subset) and male
  infertility from oligoasthenoteratozoospermia with structurally abnormal,
  short, immotile flagella. Airway disease - the dominant feature of most motile
  ciliopathies - is characteristically mild or absent, which is why ClinGen's
  Motile Ciliopathy Gene Curation Expert Panel classifies the MNS1-primary
  ciliary dyskinesia relationship as Disputed; a respiratory phenotype (neonatal
  respiratory distress, recurrent infection, chronic rhinitis, wet cough) has
  nonetheless now been documented in a minority of individuals. Fewer than twenty
  affected individuals have been reported worldwide, almost all from consanguineous
  or founder pedigrees.
parents:
- Visceral heterotaxy
- Motile ciliopathy
- Congenital Disorder
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0030070
      label: heterotaxy, visceral, 9, autosomal, with male infertility
    mapping_predicate: skos:exactMatch
    mapping_source: MONDO
    mapping_justification: >-
      MONDO:0030070 is the primary term for this entry. It carries OMIM:618948 as
      an xref and records MNS1 (HGNC:29636) as the causal gene via RO:0004003,
      both of which match the curated content of this entry.

classifications:
  harrisons_chapter:
  - classification_value: GENETICS_ENVIRONMENT_DISEASE
    notes: >-
      Autosomal recessive Mendelian motile ciliopathy; diagnosis is molecular and
      the published cohort is drawn almost entirely from consanguineous pedigrees.
    evidence:
    - reference: PMID:30148830
      reference_title: >-
        Homozygous loss-of-function mutations in MNS1 cause laterality defects and
        likely male infertility.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        we identified two recessive loss-of-function MNS1 mutations in five
        individuals from four consanguineous families
      explanation: >-
        A recessive single-gene disorder delineated in consanguineous pedigrees,
        which is what places it in the genetics chapter.
  - classification_value: CARDIOVASCULAR
    notes: >-
      The clinically dominant manifestation is a laterality defect, and complex
      congenital heart disease is the principal source of morbidity in affected
      individuals with true heterotaxy.
    evidence:
    - reference: PMID:38920647
      reference_title: >-
        Biallelic Variants in MNS1 Are Associated with Laterality Defects and
        Respiratory Involvement.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        All four affected individuals presented with laterality defects, including
        one male individual with heterotaxia and complex congenital heart defects.
      explanation: >-
        Complex congenital heart disease in the heterotaxy subset is the
        cardiovascular burden that motivates this chapter assignment.
  mechanistic_category:
  - classification_value: ciliopathy
    notes: >-
      Disease mechanism is dysfunction of motile cilia and flagella (nodal
      monocilia, respiratory cilia, sperm flagella) rather than primary-cilium
      signalling.
    evidence:
    - reference: PMID:38920647
      reference_title: >-
        Biallelic Variants in MNS1 Are Associated with Laterality Defects and
        Respiratory Involvement.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        This study represents the first observation of heterotaxia and respiratory
        disease in individuals with biallelic MNS1 variants, an important extension
        of the phenotype associated with MNS1-related motile ciliopathy disorder.
      explanation: >-
        Names MNS1-related disease a motile ciliopathy, the mechanistic category
        assigned here.

inheritance:
- name: Autosomal recessive
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >-
    All reported affected individuals carry biallelic MNS1 loss-of-function
    alleles - homozygous nonsense or frameshift variants in consanguineous and
    founder pedigrees, and compound heterozygous variants in outbred families.
    Heterozygous carriers are unaffected. Because left-right axis specification is
    randomised rather than reversed, sibships homozygous for the same allele
    segregate a mixture of situs solitus, situs inversus totalis and heterotaxy,
    so laterality status is not a reliable indicator of genotype within a family.
  evidence:
  - reference: PMID:30148830
    reference_title: >-
      Homozygous loss-of-function mutations in MNS1 cause laterality defects and
      likely male infertility.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      we identified two recessive loss-of-function MNS1 mutations in five
      individuals from four consanguineous families
    explanation: >-
      Establishes the recessive mode of inheritance in the index cohort of four
      consanguineous families.
  - reference: PMID:31534215
    reference_title: MNS1 variant associated with situs inversus and male infertility.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Genotyping of multiple family members identified randomisation of the
      laterality defects in other homozygous individuals, with all wild type or
      MNS1 c.407_410del heterozygous carriers being unaffected, consistent with an
      autosomal recessive mode of inheritance.
    explanation: >-
      Segregation in an extended Amish pedigree confirms autosomal recessive
      inheritance with unaffected heterozygous carriers, and documents that
      laterality is randomised rather than uniformly inverted among homozygotes.

genetic:
- name: MNS1
  gene_term:
    preferred_term: MNS1
    term:
      id: hgnc:29636
      label: MNS1
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  features: >-
    MNS1 (15q21.3) encodes meiosis-specific nuclear structural protein 1, a
    coiled-coil protein that is a detergent-resistant integral component of the
    motile axoneme. MNS1 self-associates into dimers and higher-order polymers and
    binds CCDC114, a subunit of the outer dynein arm docking complex, giving it a
    structural role in tethering outer dynein arms to the outer doublet
    microtubules. It is expressed in testicular germ cells, in respiratory
    epithelium, and - in mouse - in the embryonic ventral node. Reported pathogenic
    alleles are uniformly loss-of-function: homozygous nonsense (p.Arg242*,
    p.Gln203*), homozygous frameshift (the c.407_410del Amish founder allele;
    c.603_604insG), an in-frame deletion, and compound heterozygous
    frameshift/nonsense combinations.
  evidence:
  - reference: PMID:30148830
    reference_title: >-
      Homozygous loss-of-function mutations in MNS1 cause laterality defects and
      likely male infertility.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      we demonstrate that MNS1 deficiency in humans causes laterality defects
      (situs inversus) and likely male infertility and that MNS1 plays a role in
      the ODA-DC assembly
    explanation: >-
      Names MNS1 as the causal gene for this disease and states its molecular role
      in outer dynein arm docking complex assembly.
  - reference: PMID:30148830
    reference_title: >-
      Homozygous loss-of-function mutations in MNS1 cause laterality defects and
      likely male infertility.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      co-immunoprecipitation and yeast two hybrid analyses demonstrated that MNS1
      dimerizes and interacts with the ODA docking complex component CCDC114
    explanation: >-
      Biochemical interaction data establishing the molecular function of the MNS1
      protein product.
  - reference: PMID:39233552
    reference_title: Expanding MNS1 Heterotaxy Phenotype.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      MNS1 (meiosis-specific nuclear structural protein-1 gene) encodes a
      structural protein implicated in motile ciliary function and sperm flagella
      assembly.
    explanation: >-
      Independent statement of the gene product's function in motile cilia and
      sperm flagella.
  - reference: CGGV:assertion_255ba802-ece2-43c7-9089-6e54672b4f4a-2022-09-13T170000.000Z
    reference_title: MNS1 / primary ciliary dyskinesia (Disputed)
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      MNS1 | HGNC:29636 | primary ciliary dyskinesia | MONDO:0016575 | AR |
      Disputed
    explanation: >-
      ClinGen's Motile Ciliopathy Gene Curation Expert Panel disputes MNS1 as a
      cause of primary ciliary dyskinesia. This is recorded as PARTIAL because it
      constrains rather than refutes the gene-disease claim curated here: the
      disputed assertion is against the PCD entity (MONDO:0016575), not against
      HTX9 (MONDO:0030070), and reflects the characteristic absence of
      otosinopulmonary disease in MNS1 deficiency.
  variants:
  - name: MNS1 p.Arg242*
    description: >-
      Homozygous nonsense variant identified in four males with laterality defects
      and infertility from consanguineous families; the index allele for HTX9.
    evidence:
    - reference: PMID:30148830
      reference_title: >-
        Homozygous loss-of-function mutations in MNS1 cause laterality defects and
        likely male infertility.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        a homozygous nonsense mutation p.Arg242* in four males with laterality
        defects and infertility
      explanation: >-
        Directly reports the variant, its zygosity, and the associated phenotype.
  - name: MNS1 c.407_410del p.(Glu136Glyfs*16)
    description: >-
      Homozygous founder frameshift allele segregating in an extended Amish
      pedigree with situs inversus and male infertility.
    evidence:
    - reference: PMID:31534215
      reference_title: MNS1 variant associated with situs inversus and male infertility.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        we investigated the genetic cause of a form of situs inversus (SI) and male
        infertility present in multiple individuals in an extended Amish family
      explanation: >-
        Establishes the pedigree and phenotype in which this founder frameshift
        allele was identified.
  - name: MNS1 c.603_604insG p.Lys202Glufs*6
    description: >-
      Homozygous frameshift variant identified in a Han Chinese proband with severe
      oligoasthenoteratozoospermia, the fertility-only presentation of MNS1
      deficiency.
    evidence:
    - reference: PMID:33037173
      reference_title: >-
        A novel homozygous frameshift mutation in MNS1 associated with severe
        oligoasthenoteratozoospermia in humans.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        we identified a novel homozygous frameshift mutation in meiosis-specific
        nuclear structural 1 (MNS1; NM_018365: c.603_604insG: p.Lys202Glufs*6) by
        whole-exome sequencing in an OAT proband from a consanguineous Chinese
        family
      explanation: >-
        Reports the variant and the isolated infertility phenotype in which it was
        ascertained.

pathophysiology:
- name: Biallelic MNS1 Loss of Function
  biological_scale: MOLECULAR
  role: trigger
  description: >-
    Homozygous or compound heterozygous nonsense, frameshift and in-frame deletion
    alleles in MNS1 abolish production of functional MNS1 protein. Immunofluorescence
    in affected individuals shows loss of MNS1 from the axonemes and flagella where
    the wild-type protein normally resides, confirming that the reported alleles
    behave as true nulls at the protein level rather than as hypomorphs of uncertain
    consequence.
  genes:
  - preferred_term: MNS1
    term:
      id: hgnc:29636
      label: MNS1
  evidence:
  - reference: PMID:30148830
    reference_title: >-
      Homozygous loss-of-function mutations in MNS1 cause laterality defects and
      likely male infertility.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Immunofluorescence analysis further revealed that MNS1 localizes to the
      axonemes of respiratory cilia as well as sperm flagella in human.
    explanation: >-
      Establishes where wild-type MNS1 protein resides in human tissue, the
      baseline against which its loss in patients is scored.
  - reference: PMID:33037173
    reference_title: >-
      A novel homozygous frameshift mutation in MNS1 associated with severe
      oligoasthenoteratozoospermia in humans.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Immunostaining analysis showed MNS1 to be normally located in the whole-sperm
      flagella, but was absent in the proband's sperm.
    explanation: >-
      Demonstrates at the protein level that a frameshift allele results in absent
      MNS1 from the flagellum.
  downstream:
  - target: Outer Dynein Arm Docking Defect in the Motile Axoneme
    description: >-
      Absence of the MNS1 protein removes a structural component required for
      normal assembly and docking of outer dynein arms on the axonemal outer
      doublet microtubules.
    evidence:
    - reference: PMID:30148830
      reference_title: >-
        Homozygous loss-of-function mutations in MNS1 cause laterality defects and
        likely male infertility.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        we demonstrate that MNS1 deficiency in humans causes laterality defects
        (situs inversus) and likely male infertility and that MNS1 plays a role in
        the ODA-DC assembly
      explanation: >-
        Directly links MNS1 deficiency to a defect in outer dynein arm docking
        complex assembly.

- name: Outer Dynein Arm Docking Defect in the Motile Axoneme
  biological_scale: MOLECULAR
  role: central_effector
  description: >-
    MNS1 dimerises and binds CCDC114, a component of the outer dynein arm docking
    complex (ODA-DC). Without MNS1, outer dynein arms are incompletely docked onto
    the outer doublet microtubules. Crucially, the resulting ultrastructural lesion
    is subtle - a partial rather than complete loss of outer dynein arms, most
    pronounced in the distal axoneme - which distinguishes MNS1 deficiency from the
    complete ODA loss seen with DNAH5 or DNAI1 defects and accounts for the mild
    airway phenotype relative to classic primary ciliary dyskinesia.
  biological_processes:
  - preferred_term: outer dynein arm assembly
    term:
      id: GO:0036158
      label: outer dynein arm assembly
    modifier: DECREASED
  cellular_components:
  - preferred_term: axoneme
    term:
      id: GO:0005930
      label: axoneme
  evidence:
  - reference: PMID:30148830
    reference_title: >-
      Homozygous loss-of-function mutations in MNS1 cause laterality defects and
      likely male infertility.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In-depth ultrastructural analyses confirmed a subtle outer dynein arm (ODA)
      defect in the axonemes of respiratory epithelial cells resembling findings
      reported in Mns1-deficient mice.
    explanation: >-
      Documents the ultrastructural lesion in patient respiratory axonemes and
      explicitly characterises it as subtle.
  - reference: PMID:30148830
    reference_title: >-
      Homozygous loss-of-function mutations in MNS1 cause laterality defects and
      likely male infertility.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Ultrastructural analyses in the female carrying combined mutations in MNS1
      and DNAH5 indicated a role for MNS1 in the process of ODA docking (ODA-DC) in
      the distal respiratory axonemes.
    explanation: >-
      Localises the MNS1-dependent docking defect to the distal respiratory
      axoneme.
  notes: >-
    The individual in whom the distal ODA-docking phenotype was characterised also
    carried homozygous DNAH5 mutations, so the MNS1-specific contribution to that
    particular ultrastructural readout is partially confounded. See the
    mns1_pcd_boundary KNOWLEDGE_GAP discussion.
  downstream:
  - target: Nodal Cilia Motility Failure at the Left-Right Organizer
    description: >-
      The motile monocilia of the embryonic left-right organiser depend on outer
      dynein arm-driven beating to generate leftward nodal flow.
    evidence:
    - reference: PMID:30148830
      reference_title: >-
        Homozygous loss-of-function mutations in MNS1 cause laterality defects and
        likely male infertility.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Consistent with the laterality defects observed in these individuals, we
        found Mns1 to be expressed in mouse embryonic ventral node.
      explanation: >-
        Places MNS1 expression at the left-right organiser, the anatomical link
        between the axonemal defect and the laterality phenotype.
  - target: Sperm Flagellar Axoneme Assembly Failure
    description: >-
      The sperm flagellum is built on the same 9+2 axonemal template and requires
      MNS1 as an integral structural component.
    evidence:
    - reference: PMID:30148830
      reference_title: >-
        Homozygous loss-of-function mutations in MNS1 cause laterality defects and
        likely male infertility.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Immunofluorescence analysis further revealed that MNS1 localizes to the
        axonemes of respiratory cilia as well as sperm flagella in human.
      explanation: >-
        Establishes MNS1 as a component of the human sperm flagellar axoneme,
        licensing the causal edge to flagellar assembly failure.
  - target: Respiratory Ciliary Dysfunction
    description: >-
      Partial outer dynein arm loss in airway multiciliated cells impairs
      mucociliary clearance in a subset of affected individuals.
    evidence:
    - reference: PMID:38920647
      reference_title: >-
        Biallelic Variants in MNS1 Are Associated with Laterality Defects and
        Respiratory Involvement.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Accordingly, immunofluorescence analysis showed the absence of MNS1 from
        the respiratory epithelial cells of this individual.
      explanation: >-
        Ties the respiratory phenotype in an affected child to demonstrated loss of
        MNS1 from her own airway epithelium.
  - target: Partial absence of outer dynein arms in respiratory cilia
    description: >-
      The docking defect is what transmission electron microscopy of patient
      respiratory cilia visualises as partial outer dynein arm loss.
    evidence:
    - reference: PMID:30148830
      reference_title: >-
        Homozygous loss-of-function mutations in MNS1 cause laterality defects and
        likely male infertility.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        In-depth ultrastructural analyses confirmed a subtle outer dynein arm (ODA)
        defect in the axonemes of respiratory epithelial cells resembling findings
        reported in Mns1-deficient mice.
      explanation: >-
        The ultrastructural readout of the docking defect in patient material.

- name: Nodal Cilia Motility Failure at the Left-Right Organizer
  biological_scale: CELLULAR
  role: intermediate
  conforms_to: "ciliopathy_dysfunction#Motile Cilia Beat Dysfunction"
  description: >-
    During gastrulation, motile monocilia at the ventral node beat to drive a
    leftward extraembryonic fluid flow that is the earliest known symmetry-breaking
    event in the vertebrate embryo. MNS1 is expressed in the mouse ventral node,
    and MNS1 deficiency compromises the outer dynein arm machinery that powers this
    beat, so nodal flow fails to be established robustly.
  cell_types:
  - preferred_term: ciliated epithelial cell
    term:
      id: CL:0000067
      label: ciliated epithelial cell
  biological_processes:
  - preferred_term: cilium movement
    term:
      id: GO:0003341
      label: cilium movement
    modifier: DECREASED
  - preferred_term: determination of left/right symmetry
    term:
      id: GO:0007368
      label: determination of left/right symmetry
    modifier: ABNORMAL
  evidence:
  - reference: PMID:30148830
    reference_title: >-
      Homozygous loss-of-function mutations in MNS1 cause laterality defects and
      likely male infertility.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Consistent with the laterality defects observed in these individuals, we
      found Mns1 to be expressed in mouse embryonic ventral node.
    explanation: >-
      Expression at the left-right organiser is the evidence that MNS1 acts at this
      node of the mechanism.
  - reference: PMID:31534215
    reference_title: MNS1 variant associated with situs inversus and male infertility.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This study identifies an MNS1 variant as a cause of laterality defects and
      male infertility in humans, mirroring findings in Mns1-deficient mice which
      also display male infertility and randomisation of left-right asymmetry of
      internal organs, confirming a crucial role for MNS1 in nodal cilia and sperm
      flagella formation and function.
    explanation: >-
      Explicitly assigns MNS1 a crucial role in nodal cilia formation and function,
      the conformance claim of this node.
  downstream:
  - target: Randomization of Left-Right Axis Specification
    description: >-
      Absent or insufficient nodal flow leaves the left-right axis unspecified, so
      situs is determined stochastically in each embryo.

- name: Respiratory Ciliary Dysfunction
  biological_scale: CELLULAR
  role: intermediate
  conforms_to: "ciliopathy_dysfunction#Motile Cilia Beat Dysfunction"
  description: >-
    MNS1 is present in the axonemes of human respiratory cilia, and affected
    individuals show its absence from airway epithelium together with a partial
    outer dynein arm defect. Unlike classic primary ciliary dyskinesia, however,
    the airway consequence is variable and frequently absent: most reported
    individuals have no significant otosinopulmonary disease, and the airway arm of
    the module is only partially manifested. Where it does occur it presents as
    neonatal respiratory distress, recurrent respiratory tract infection, chronic
    rhinitis and wet cough rather than established bronchiectasis.
  cell_types:
  - preferred_term: multiciliated airway epithelial cell
    term:
      id: CL:0002145
      label: multiciliated columnar cell of tracheobronchial tree
  locations:
  - preferred_term: respiratory airway
    term:
      id: UBERON:0001005
      label: respiratory airway
  biological_processes:
  - preferred_term: epithelial cilium movement involved in extracellular fluid movement
    term:
      id: GO:0003351
      label: epithelial cilium movement involved in extracellular fluid movement
    modifier: DECREASED
  evidence:
  - reference: PMID:38920647
    reference_title: >-
      Biallelic Variants in MNS1 Are Associated with Laterality Defects and
      Respiratory Involvement.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This study represents the first observation of heterotaxia and respiratory
      disease in individuals with biallelic MNS1 variants, an important extension
      of the phenotype associated with MNS1-related motile ciliopathy disorder.
    explanation: >-
      Establishes that respiratory disease is part of the MNS1 phenotype, while its
      framing as a novel extension records that it is not the usual presentation.
  - reference: PMID:38920647
    reference_title: >-
      Biallelic Variants in MNS1 Are Associated with Laterality Defects and
      Respiratory Involvement.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Two other individuals with hypomorphic variants showed laterality defects and
      mild respiratory phenotype.
    explanation: >-
      Records that where airway involvement occurs in MNS1 deficiency it is
      typically mild, which is the qualification this node carries relative to the
      module's airway arm.
  notes: >-
    Conformance to the module's motile-cilia arm is asserted for the mechanism (MNS1
    is demonstrably absent from patient airway axonemes, with a partial ODA defect),
    not for a claim that MNS1 deficiency reproduces primary ciliary dyskinesia.
    ClinGen classifies the MNS1-PCD gene-disease relationship as Disputed.
  downstream:
  - target: Recurrent respiratory tract infections
    description: >-
      Impaired mucociliary clearance predisposes to recurrent lower and upper
      airway infection in the minority of individuals with an airway phenotype.
    evidence:
    - reference: PMID:38920647
      reference_title: >-
        Biallelic Variants in MNS1 Are Associated with Laterality Defects and
        Respiratory Involvement.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Interestingly, a single affected six-year-old girl homozygous for an MNS1
        nonsense variant presented with a history of neonatal respiratory distress
        syndrome, recurrent respiratory tract infections, chronic rhinitis, and wet
        cough.
      explanation: >-
        The airway phenotype observed in the individual with demonstrated loss of
        MNS1 from her respiratory epithelium.
  - target: Chronic rhinitis
    description: Upper-airway manifestation of impaired mucociliary clearance.
    evidence:
    - reference: PMID:38920647
      reference_title: >-
        Biallelic Variants in MNS1 Are Associated with Laterality Defects and
        Respiratory Involvement.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Interestingly, a single affected six-year-old girl homozygous for an MNS1
        nonsense variant presented with a history of neonatal respiratory distress
        syndrome, recurrent respiratory tract infections, chronic rhinitis, and wet
        cough.
      explanation: Chronic rhinitis is enumerated in the same airway presentation.
  - target: Neonatal respiratory distress
    description: >-
      Failure of perinatal airway clearance, the earliest airway manifestation of
      motile ciliary dysfunction.
    evidence:
    - reference: PMID:38920647
      reference_title: >-
        Biallelic Variants in MNS1 Are Associated with Laterality Defects and
        Respiratory Involvement.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Interestingly, a single affected six-year-old girl homozygous for an MNS1
        nonsense variant presented with a history of neonatal respiratory distress
        syndrome, recurrent respiratory tract infections, chronic rhinitis, and wet
        cough.
      explanation: Neonatal respiratory distress syndrome is explicitly reported.
  - target: Recurrent otitis media
    description: >-
      Middle-ear clearance depends on the same motile cilia, so otitis media is the
      mildest and most frequently isolated airway manifestation.
    evidence:
    - reference: PMID:31534215
      reference_title: MNS1 variant associated with situs inversus and male infertility.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        All affected individuals were clinically assessed, no PCD symptoms were
        reported, with the exception of IX-1 who suffered recurrent otitis media.
      explanation: >-
        Recurrent otitis media was the single airway manifestation in an otherwise
        PCD-symptom-free Amish pedigree, which is exactly the mild, isolated form
        this edge describes.

- name: Sperm Flagellar Axoneme Assembly Failure
  biological_scale: CELLULAR
  role: intermediate
  description: >-
    MNS1 is an integral, detergent-resistant component of the sperm flagellum. In
    its absence the flagellar axoneme is not correctly assembled: the 9+2
    microtubule arrangement and the surrounding outer dense fibres are disrupted,
    and outer doublet microtubules show ultrastructural disturbance in human
    patients. Because MNS1 loss acts during spermiogenesis - the post-meiotic
    morphogenesis of the round spermatid into a spermatozoon - both the number and
    the structure of the resulting gametes are affected.
  cell_types:
  - preferred_term: sperm
    term:
      id: CL:0000019
      label: sperm
  biological_processes:
  - preferred_term: sperm axoneme assembly
    term:
      id: GO:0007288
      label: sperm axoneme assembly
    modifier: DECREASED
  - preferred_term: spermatid development
    term:
      id: GO:0007286
      label: spermatid development
    modifier: ABNORMAL
  evidence:
  - reference: PMID:33037173
    reference_title: >-
      A novel homozygous frameshift mutation in MNS1 associated with severe
      oligoasthenoteratozoospermia in humans.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Abnormal flagellum morphology and ultrastructural disturbances in outer
      doublet microtubules were observed in the proband's sperm.
    explanation: >-
      Human ultrastructural evidence that MNS1 loss disrupts flagellar axoneme
      architecture.
  - reference: PMID:33037173
    reference_title: >-
      A novel homozygous frameshift mutation in MNS1 associated with severe
      oligoasthenoteratozoospermia in humans.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In our study, MNS1 defect was associated with missing peripheral DMTs (2–4
      out of 9) and absent ODAs in humans
    explanation: >-
      Ties the sperm flagellar defect specifically to loss of outer dynein arms,
      which is the same lesion the upstream Outer Dynein Arm Docking Defect node
      describes. This is what makes the axoneme node a continuation of the ODA
      docking defect in sperm rather than an independent spermatogenic failure.
  - reference: PMID:22396656
    reference_title: MNS1 is essential for spermiogenesis and motile ciliary functions in mice.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      We find that MNS1 is expressed in the germ cells in the testes and localizes
      to sperm flagella in a detergent-resistant manner, indicating that it is an
      integral component of flagella.
    explanation: >-
      Establishes MNS1 as a structural component of the flagellum rather than a
      transient assembly factor.
  - reference: PMID:22396656
    reference_title: MNS1 is essential for spermiogenesis and motile ciliary functions in mice.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      These results demonstrate that MNS1 is essential for spermiogenesis, the
      assembly of sperm flagella, and motile ciliary functions.
    explanation: >-
      Summary statement of the mouse loss-of-function phenotype underpinning this
      node.
  downstream:
  - target: Oligoasthenoteratozoospermia and Male Infertility
    description: >-
      Failure of flagellar assembly during spermiogenesis yields few, malformed and
      immotile spermatozoa.
    evidence:
    - reference: PMID:22396656
      reference_title: MNS1 is essential for spermiogenesis and motile ciliary functions in mice.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        MNS1-deficient males are sterile, as they exhibit a sharp reduction in
        sperm production and the remnant sperm are immotile with abnormal short
        tails.
      explanation: >-
        Directly connects flagellar assembly failure to reduced sperm number,
        abnormal morphology, immotility and sterility.

- name: Randomization of Left-Right Axis Specification
  biological_scale: ORGANISM
  role: consequence
  description: >-
    With nodal flow absent, left-right identity is assigned stochastically rather
    than deterministically. Some affected individuals develop normal situs solitus,
    some develop mirror-image situs inversus totalis, and a further fraction fails
    to establish a coherent axis at all and develops true heterotaxy (situs
    ambiguus) with discordant thoracic and abdominal arrangement and complex
    congenital heart disease. This randomisation - as opposed to consistent
    reversal - is the signature of a nodal-cilium laterality defect and explains the
    intrafamilial variability seen in MNS1 pedigrees.
  biological_processes:
  - preferred_term: determination of left/right symmetry
    term:
      id: GO:0007368
      label: determination of left/right symmetry
    modifier: ABNORMAL
  evidence:
  - reference: PMID:31534215
    reference_title: MNS1 variant associated with situs inversus and male infertility.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Genotyping of multiple family members identified randomisation of the
      laterality defects in other homozygous individuals, with all wild type or
      MNS1 c.407_410del heterozygous carriers being unaffected, consistent with an
      autosomal recessive mode of inheritance.
    explanation: >-
      Documents randomisation, rather than uniform inversion, of laterality among
      homozygotes in a single extended pedigree.
  - reference: PMID:38920647
    reference_title: >-
      Biallelic Variants in MNS1 Are Associated with Laterality Defects and
      Respiratory Involvement.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A broad spectrum of laterality defects including situs inversus totalis and
      heterotaxia was confirmed.
    explanation: >-
      Confirms that the laterality outcome spans complete mirror-imaging through to
      true heterotaxy.
  downstream:
  - target: Laterality defect
    description: >-
      Abnormal left-right arrangement of the thoraco-abdominal organs is the direct
      clinical expression of a randomised left-right axis.
    evidence:
    - reference: PMID:38920647
      reference_title: >-
        Biallelic Variants in MNS1 Are Associated with Laterality Defects and
        Respiratory Involvement.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        A broad spectrum of laterality defects including situs inversus totalis and
        heterotaxia was confirmed.
      explanation: >-
        The clinical laterality spectrum observed in MNS1-deficient individuals.
  - target: Situs inversus totalis
    description: >-
      Complete mirror-image reversal is the outcome when a coherent but inverted
      axis is established.
    evidence:
    - reference: PMID:31534215
      reference_title: MNS1 variant associated with situs inversus and male infertility.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        IX-5 died from meningitis aged 5 months and was discovered to have
        heterotaxy, subsequently a diagnosis of SI was made in IX-2, IX-1, VIII-15
        and VII-9.
      explanation: >-
        Names the situs inversus outcome directly: four homozygotes in this pedigree
        received an SI diagnosis while a fifth had heterotaxy, so situs inversus is
        one stochastic outcome of the randomised axis rather than the uniform result
        of a directed reversal.
  - target: Complex congenital heart disease
    description: >-
      When no coherent axis is established, cardiac segments are discordantly
      arranged and complex structural heart disease results.
    evidence:
    - reference: PMID:38920647
      reference_title: >-
        Biallelic Variants in MNS1 Are Associated with Laterality Defects and
        Respiratory Involvement.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        All four affected individuals presented with laterality defects, including
        one male individual with heterotaxia and complex congenital heart defects.
      explanation: >-
        Couples the heterotaxy outcome to complex congenital heart disease in an
        affected individual.
  - target: Asplenia
    description: >-
      Splenic agenesis accompanies right isomerism, the bilateral-right-sidedness
      form of a failed left-right axis.
    evidence:
    - reference: PMID:38920647
      reference_title: >-
        Biallelic Variants in MNS1 Are Associated with Laterality Defects and
        Respiratory Involvement.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Individual EX-1II1 presented with right isomerism, asplenia, and complex
        congenital heart disease that required surgical intervention.
      explanation: >-
        Directly links asplenia to right isomerism in an MNS1-deficient individual.

- name: Oligoasthenoteratozoospermia and Male Infertility
  biological_scale: ORGANISM
  role: consequence
  description: >-
    Affected males have severe oligoasthenoteratozoospermia: reduced sperm counts,
    absent or near-absent progressive motility, and abnormal head and tail
    morphology. Infertility is the consistent reproductive outcome. In the one
    reported attempt, intracytoplasmic sperm injection did not rescue fertility,
    which is consistent with the defect being structural and gamete-intrinsic
    rather than purely motility-limited.
  evidence:
  - reference: PMID:33037173
    reference_title: >-
      A novel homozygous frameshift mutation in MNS1 associated with severe
      oligoasthenoteratozoospermia in humans.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The semen examination results of the proband were as follows: semen volume,
      3.4 ml; sperm concentration, 1.8 × 106 ml−1; and percentage progressive
      motility, 5.8%.
    explanation: >-
      The measured semen phenotype of the MNS1-deficient proband. All three
      components of the oligoasthenoteratozoospermia triad are quantified in the
      same individual and each falls below the WHO lower reference limit, which is
      what makes this node an observed outcome rather than a definitional label.
  - reference: PMID:30148830
    reference_title: >-
      Homozygous loss-of-function mutations in MNS1 cause laterality defects and
      likely male infertility.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      a homozygous nonsense mutation p.Arg242* in four males with laterality
      defects and infertility
    explanation: >-
      Reports infertility in all four homozygous males in the index cohort.
      Recorded as PARTIAL because the same paper qualifies the association as
      likely male infertility, formal semen analysis not being available for every
      individual.
  downstream:
  - target: Male infertility
    description: >-
      The reproductive endpoint of the flagellar defect in affected males.
    evidence:
    - reference: PMID:31534215
      reference_title: MNS1 variant associated with situs inversus and male infertility.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        This study identifies an MNS1 variant as a cause of laterality defects and
        male infertility in humans, mirroring findings in Mns1-deficient mice which
        also display male infertility and randomisation of left-right asymmetry of
        internal organs, confirming a crucial role for MNS1 in nodal cilia and sperm
        flagella formation and function.
      explanation: >-
        States male infertility as the consequence of MNS1 deficiency in humans.
  - target: Reduced sperm motility
    description: >-
      Immotility is the functional component of the oligoasthenoteratozoospermia
      triad.
    evidence:
    - reference: PMID:33037173
      reference_title: >-
        A novel homozygous frameshift mutation in MNS1 associated with severe
        oligoasthenoteratozoospermia in humans.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        The semen examination results of the proband were as follows: semen volume,
        3.4 ml; sperm concentration, 1.8 × 106 ml−1; and percentage progressive
        motility, 5.8%.
      explanation: >-
        Progressive motility measured at 5.8% in the MNS1-deficient proband, far
        below the WHO lower reference limit.
  - target: Oligozoospermia
    description: The quantitative component of the oligoasthenoteratozoospermia triad.
    evidence:
    - reference: PMID:33037173
      reference_title: >-
        A novel homozygous frameshift mutation in MNS1 associated with severe
        oligoasthenoteratozoospermia in humans.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        The semen examination results of the proband were as follows: semen volume,
        3.4 ml; sperm concentration, 1.8 × 106 ml−1; and percentage progressive
        motility, 5.8%.
      explanation: >-
        Sperm concentration measured at 1.8 million per ml in the MNS1-deficient
        proband, an order of magnitude below the WHO lower reference limit.
  - target: Abnormal sperm morphology
    description: The structural component of the oligoasthenoteratozoospermia triad.
    evidence:
    - reference: PMID:33037173
      reference_title: >-
        A novel homozygous frameshift mutation in MNS1 associated with severe
        oligoasthenoteratozoospermia in humans.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Abnormal flagellum morphology and ultrastructural disturbances in outer
        doublet microtubules were observed in the proband's sperm.
      explanation: >-
        Direct morphological description of the patient's spermatozoa.

phenotypes:
- category: Developmental
  name: Laterality defect
  description: >-
    The defining clinical feature. Affected individuals present with abnormal
    left-right arrangement of the thoraco-abdominal organs, ranging from complete
    mirror-image situs inversus totalis to true heterotaxy with discordant organ
    arrangement.
  phenotype_term:
    preferred_term: Heterotaxy
    term:
      id: HP:0030853
      label: Heterotaxy
  frequency: FREQUENT
  evidence:
  - reference: PMID:38920647
    reference_title: >-
      Biallelic Variants in MNS1 Are Associated with Laterality Defects and
      Respiratory Involvement.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A broad spectrum of laterality defects including situs inversus totalis and
      heterotaxia was confirmed.
    explanation: >-
      Confirms laterality defects, including frank heterotaxy, across the reported
      cohort.
  - reference: PMID:30148830
    reference_title: >-
      Homozygous loss-of-function mutations in MNS1 cause laterality defects and
      likely male infertility.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      a homozygous nonsense mutation p.Arg242* in four males with laterality
      defects and infertility
    explanation: >-
      Establishes the association: all five reported homozygotes across four
      consanguineous families had laterality defects. These individuals were
      ascertained through those defects, so the count fixes the disease-phenotype
      association but cannot estimate its frequency; the band is carried by the
      genotype-first pedigree count below.
  - reference: PMID:31534215
    reference_title: MNS1 variant associated with situs inversus and male infertility.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Six individuals were found to be homozygous for the MNS1
      NM_018365.2:c.407_410del variant, of whom four (67%) exhibited SI and two
      (33%) exhibited situs solitus.
    explanation: >-
      The one genotype-first denominator available for this disorder: 26 members of
      the Amish pedigree were genotyped and clinically assessed, and four of the six
      homozygotes so identified (67%) had a laterality defect while two had normal
      situs. 67% sits in the frequent (30-79%) band. The two situs solitus
      homozygotes are what the randomisation mechanism predicts, and are why a very
      frequent (80-99%) band would contradict this entry's central claim.

- category: Developmental
  name: Situs inversus totalis
  description: >-
    Complete mirror-image reversal of thoracic and abdominal viscera, the most
    commonly reported laterality outcome in MNS1 deficiency and the presentation of
    the Amish founder pedigree.
  phenotype_term:
    preferred_term: Situs inversus totalis
    term:
      id: HP:0001696
      label: Situs inversus totalis
  evidence:
  - reference: PMID:31534215
    reference_title: MNS1 variant associated with situs inversus and male infertility.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      we investigated the genetic cause of a form of situs inversus (SI) and male
      infertility present in multiple individuals in an extended Amish family
    explanation: >-
      Situs inversus was the ascertaining phenotype in this pedigree.
  - reference: PMID:39233552
    reference_title: Expanding MNS1 Heterotaxy Phenotype.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The first patient was a female presenting complete situs inversus and unusual
      symptoms, including severe myopia and dental agenesis of 10 permanent teeth.
    explanation: >-
      Independent report of complete situs inversus in a compound heterozygous
      individual.

- category: Cardiovascular
  name: Complex congenital heart disease
  description: >-
    Where the laterality defect is true heterotaxy rather than complete inversion,
    the cardiac segments are discordantly arranged and complex structural heart
    disease results. This is the principal determinant of morbidity in affected
    individuals.
  phenotype_term:
    preferred_term: Complex congenital heart malformation
    term:
      id: HP:0001627
      label: Abnormal heart morphology
  evidence:
  - reference: PMID:38920647
    reference_title: >-
      Biallelic Variants in MNS1 Are Associated with Laterality Defects and
      Respiratory Involvement.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All four affected individuals presented with laterality defects, including
      one male individual with heterotaxia and complex congenital heart defects.
    explanation: >-
      Reports complex congenital heart defects in the individual with true
      heterotaxy.
  notes: >-
    HP:0001627 (Abnormal heart morphology) is used because HPO has no single term
    for complex congenital heart disease; the preferred_term carries the intended
    clinical granularity.

- category: Developmental
  name: Asplenia
  description: >-
    Splenic agenesis, reported with right isomerism (bilateral right-sidedness) in
    an MNS1-deficient individual with complex congenital heart disease. Asplenia is
    the classic splenic accompaniment of right isomerism and carries a lifelong
    risk of overwhelming encapsulated-organism sepsis, so it changes management
    (immunisation, antibiotic prophylaxis) rather than being an incidental
    anatomical note.
  phenotype_term:
    preferred_term: Asplenia
    term:
      id: HP:0001746
      label: Asplenia
  evidence:
  - reference: PMID:38920647
    reference_title: >-
      Biallelic Variants in MNS1 Are Associated with Laterality Defects and
      Respiratory Involvement.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Individual EX-1II1 presented with right isomerism, asplenia, and complex
      congenital heart disease that required surgical intervention.
    explanation: >-
      Reports asplenia in an MNS1-deficient individual, together with the right
      isomerism that mechanistically explains it.

- category: Respiratory
  name: Recurrent otitis media
  description: >-
    Middle-ear disease is the mildest and most frequently isolated airway
    manifestation of MNS1 deficiency. In the Amish founder pedigree it was the only
    airway symptom in any affected individual, the rest being explicitly free of
    primary ciliary dyskinesia symptoms - which is the clearest single illustration
    of how attenuated the airway arm is in this disorder relative to classic PCD.
  phenotype_term:
    preferred_term: Recurrent otitis media
    term:
      id: HP:0000403
      label: Recurrent otitis media
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:31534215
    reference_title: MNS1 variant associated with situs inversus and male infertility.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All affected individuals were clinically assessed, no PCD symptoms were
      reported, with the exception of IX-1 who suffered recurrent otitis media.
    explanation: >-
      IX-1 was the only individual in this pedigree with any airway symptom; every
      other assessed homozygote was explicitly free of PCD symptoms. Against the six
      homozygotes the same paper reports, that is 1/6 (17%), inside the occasional
      (5-29%) band.

- category: Reproductive
  name: Male infertility
  description: >-
    Consistently reported in homozygous adult males. Infertility is primary and
    gamete-intrinsic; assisted reproduction by intracytoplasmic sperm injection was
    unsuccessful in the one reported attempt.
  phenotype_term:
    preferred_term: Male infertility
    term:
      id: HP:0003251
      label: Male infertility
  evidence:
  - reference: PMID:31534215
    reference_title: MNS1 variant associated with situs inversus and male infertility.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This study identifies an MNS1 variant as a cause of laterality defects and
      male infertility in humans, mirroring findings in Mns1-deficient mice which
      also display male infertility and randomisation of left-right asymmetry of
      internal organs, confirming a crucial role for MNS1 in nodal cilia and sperm
      flagella formation and function.
    explanation: >-
      States male infertility as an established consequence of the MNS1 variant in
      humans.
  - reference: PMID:33037173
    reference_title: >-
      A novel homozygous frameshift mutation in MNS1 associated with severe
      oligoasthenoteratozoospermia in humans.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A total of three intracytoplasmic sperm injection cycles were carried out for
      the proband's wife, but they all failed to lead to a successful pregnancy.
    explanation: >-
      Documents failure of assisted reproduction, the practical severity of the
      infertility phenotype.

- category: Reproductive
  name: Reduced sperm motility
  description: >-
    Spermatozoa are immotile or severely hypomotile because the flagellar axoneme
    lacks its normal outer dynein arm complement and 9+2 organisation.
  phenotype_term:
    preferred_term: Reduced sperm motility
    term:
      id: HP:0012207
      label: Reduced sperm motility
  evidence:
  - reference: PMID:33037173
    reference_title: >-
      A novel homozygous frameshift mutation in MNS1 associated with severe
      oligoasthenoteratozoospermia in humans.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The semen examination results of the proband were as follows: semen volume,
      3.4 ml; sperm concentration, 1.8 × 106 ml−1; and percentage progressive
      motility, 5.8%.
    explanation: >-
      Progressive motility measured at 5.8% in the MNS1-deficient proband, far
      below the WHO lower reference limit. A measured value in a named individual
      rather than a definition of the term.
  - reference: PMID:22396656
    reference_title: MNS1 is essential for spermiogenesis and motile ciliary functions in mice.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      MNS1-deficient males are sterile, as they exhibit a sharp reduction in sperm
      production and the remnant sperm are immotile with abnormal short tails.
    explanation: >-
      Mouse null spermatozoa are immotile. Kept as MODEL_ORGANISM alongside the
      human oligoasthenoteratozoospermia report rather than substituting for it.

- category: Reproductive
  name: Oligozoospermia
  description: Reduced sperm concentration, part of the oligoasthenoteratozoospermia phenotype.
  phenotype_term:
    preferred_term: Oligozoospermia
    term:
      id: HP:0000798
      label: Oligozoospermia
  evidence:
  - reference: PMID:33037173
    reference_title: >-
      A novel homozygous frameshift mutation in MNS1 associated with severe
      oligoasthenoteratozoospermia in humans.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The semen examination results of the proband were as follows: semen volume,
      3.4 ml; sperm concentration, 1.8 × 106 ml−1; and percentage progressive
      motility, 5.8%.
    explanation: >-
      Sperm concentration measured at 1.8 million per ml in the MNS1-deficient
      proband, an order of magnitude below the WHO lower reference limit.

- category: Reproductive
  name: Abnormal sperm morphology
  description: >-
    Spermatozoa show abnormal head and tail morphology, with short and malformed
    flagella and disorganised outer doublet microtubules.
  phenotype_term:
    preferred_term: Abnormal sperm morphology
    term:
      id: HP:0012864
      label: Abnormal sperm morphology
  evidence:
  - reference: PMID:33037173
    reference_title: >-
      A novel homozygous frameshift mutation in MNS1 associated with severe
      oligoasthenoteratozoospermia in humans.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Abnormal flagellum morphology and ultrastructural disturbances in outer
      doublet microtubules were observed in the proband's sperm.
    explanation: >-
      Direct morphological and ultrastructural description of the patient's
      spermatozoa.

- category: Respiratory
  name: Recurrent respiratory tract infections
  description: >-
    Reported in a minority of affected individuals. This is an extension of the
    originally described phenotype and is not the usual presentation of MNS1
    deficiency; most affected individuals have no significant airway disease.
  phenotype_term:
    preferred_term: Recurrent respiratory infections
    term:
      id: HP:0002205
      label: Recurrent respiratory infections
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:38920647
    reference_title: >-
      Biallelic Variants in MNS1 Are Associated with Laterality Defects and
      Respiratory Involvement.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Interestingly, a single affected six-year-old girl homozygous for an MNS1
      nonsense variant presented with a history of neonatal respiratory distress
      syndrome, recurrent respiratory tract infections, chronic rhinitis, and wet
      cough.
    explanation: >-
      One of five newly reported individuals, framed by the authors as noteworthy
      precisely because it is unusual, had a pronounced respiratory phenotype;
      combined with the two further individuals reported to have only a mild
      respiratory phenotype this supports an occasional (5-29%) band for clinically
      significant recurrent infection.

- category: Respiratory
  name: Chronic rhinitis
  description: >-
    Part of the airway phenotype documented in the minority of MNS1-deficient
    individuals with respiratory involvement.
  phenotype_term:
    preferred_term: Chronic rhinitis
    term:
      id: HP:0002257
      label: Chronic rhinitis
  evidence:
  - reference: PMID:38920647
    reference_title: >-
      Biallelic Variants in MNS1 Are Associated with Laterality Defects and
      Respiratory Involvement.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Interestingly, a single affected six-year-old girl homozygous for an MNS1
      nonsense variant presented with a history of neonatal respiratory distress
      syndrome, recurrent respiratory tract infections, chronic rhinitis, and wet
      cough.
    explanation: >-
      Chronic rhinitis is explicitly enumerated in the respiratory presentation.

- category: Respiratory
  name: Neonatal respiratory distress
  description: >-
    Neonatal respiratory distress syndrome, a recognised early presentation of
    motile ciliopathies, was reported in the individual with the most pronounced
    MNS1 airway phenotype.
  phenotype_term:
    preferred_term: Neonatal respiratory distress
    term:
      id: HP:0002643
      label: Neonatal respiratory distress
  evidence:
  - reference: PMID:38920647
    reference_title: >-
      Biallelic Variants in MNS1 Are Associated with Laterality Defects and
      Respiratory Involvement.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Interestingly, a single affected six-year-old girl homozygous for an MNS1
      nonsense variant presented with a history of neonatal respiratory distress
      syndrome, recurrent respiratory tract infections, chronic rhinitis, and wet
      cough.
    explanation: >-
      Neonatal respiratory distress syndrome is explicitly reported.

- category: Cellular
  name: Partial absence of outer dynein arms in respiratory cilia
  description: >-
    Transmission electron microscopy of respiratory epithelial cells shows a subtle,
    partial loss of outer dynein arms, most marked distally. The subtlety of this
    lesion, compared with the complete ODA loss of DNAH5- or DNAI1-related disease,
    is the ultrastructural correlate of the mild airway phenotype.
  phenotype_term:
    preferred_term: Absent outer dynein arms
    term:
      id: HP:0012256
      label: Absent outer dynein arms
  diagnostic: true
  evidence:
  - reference: PMID:30148830
    reference_title: >-
      Homozygous loss-of-function mutations in MNS1 cause laterality defects and
      likely male infertility.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In-depth ultrastructural analyses confirmed a subtle outer dynein arm (ODA)
      defect in the axonemes of respiratory epithelial cells resembling findings
      reported in Mns1-deficient mice.
    explanation: >-
      Recorded as PARTIAL because the defect described is subtle and partial,
      whereas HP:0012256 (Absent outer dynein arms) names complete absence; the HPO
      term is the closest available and the preferred_term and description carry
      the qualification.

prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    Fewer than twenty affected individuals have been reported since the disease was
    delineated in 2018: five in the index cohort of four consanguineous families,
    an extended Amish founder pedigree, five individuals from four further
    families, three individuals in a French/GeneMatcher report, one Han Chinese
    proband ascertained through infertility, and single cases in heterotaxy cohort
    studies. No population prevalence estimate exists.
  evidence:
  - reference: PMID:39233552
    reference_title: Expanding MNS1 Heterotaxy Phenotype.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We add here new cases with the ultra-rare MNS1-related disorder and provide a
      review of all published individuals.
    explanation: >-
      The most recent review of all published individuals characterises the
      disorder as ultra-rare.
  - reference: PMID:39233552
    reference_title: Expanding MNS1 Heterotaxy Phenotype.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      To date, two different homozygous MNS1 variants have been associated with
      autosomal recessive visceral heterotaxy
    explanation: >-
      Quantifies how small the reported allelic series was at the time of the most
      recent review.
- population: Consanguineous heterotaxy cohort, Saudi Arabia
  measure_type: CASES_IN_LITERATURE
  prevalence_class: UNKNOWN
  notes: >-
    MNS1 was one of eight autosomal recessive heterotaxy genes identified in a
    consecutively recruited consanguineous cohort of 24 affected individuals from
    19 families, illustrating that MNS1 is a recurring but individually minor
    contributor to the genetic architecture of heterotaxy.
  evidence:
  - reference: PMID:39513328
    reference_title: Genetic Analysis of Heterotaxy in a Consanguineous Cohort.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Genetic analysis, with exome sequencing, genome sequencing, or multigene
      panel, detected 9 unique variants, 7 of which were novel, in 8 genes known to
      be implicated in autosomal recessive form of HTX (C1orf127, CCDC39, CIROP,
      DNAAF3, DNAH5, DNAH9, MMP21, and MNS1) providing a yield of 42.1%.
    explanation: >-
      Places MNS1 among the recurrently implicated autosomal recessive heterotaxy
      genes in a consanguineous population.

animal_models:
- name: Mns1 knockout mouse
  species: Mouse
  genotype: Mns1 null (homozygous)
  publication: PMID:22396656
  description: >-
    The founding loss-of-function model for MNS1 deficiency. Mns1-null males are
    sterile with markedly reduced sperm production and immotile, short-tailed
    spermatozoa in which the 9+2 microtubule arrangement and outer dense fibres are
    disrupted. The mice also display situs inversus and hydrocephalus, and their
    tracheal motile cilia lack a subset of outer dynein arms - the same partial ODA
    lesion later found in human patients.
  evidence:
  - reference: PMID:22396656
    reference_title: MNS1 is essential for spermiogenesis and motile ciliary functions in mice.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Here, we report that MNS1, a coiled-coil protein of unknown function, is
      essential for spermiogenesis.
    explanation: >-
      Establishes the Mns1-null mouse as a characterised loss-of-function model of
      the gene curated here.
  modeled_mechanisms:
  - target: Sperm Flagellar Axoneme Assembly Failure
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      The mouse null reproduces the human flagellar assembly defect at both the
      light-microscopic (short, immotile tails) and ultrastructural (disrupted 9+2
      axoneme and outer dense fibres) level.
    limitations: >-
      Mouse sterility is complete, whereas the human phenotype is reported as
      severe oligoasthenoteratozoospermia with residual sperm production; the human
      quantitative severity is therefore not identical.
    readouts:
    - name: Sperm production and flagellar ultrastructure
      target: Sperm Flagellar Axoneme Assembly Failure
      direction: DECREASED
      interpretation: >-
        Reduced sperm output with disrupted axonemal and outer dense fibre
        architecture is the structural correlate of the flagellar assembly node.
      evidence:
      - reference: PMID:22396656
        reference_title: >-
          MNS1 is essential for spermiogenesis and motile ciliary functions in
          mice.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          MNS1-deficient males are sterile, as they exhibit a sharp reduction in
          sperm production and the remnant sperm are immotile with abnormal short
          tails.
        explanation: >-
          Reports the measured reduction in sperm production and the flagellar
          abnormality.
    evidence:
    - reference: PMID:22396656
      reference_title: MNS1 is essential for spermiogenesis and motile ciliary functions in mice.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        These results demonstrate that MNS1 is essential for spermiogenesis, the
        assembly of sperm flagella, and motile ciliary functions.
      explanation: >-
        Establishes the model as informative for the flagellar assembly mechanism.
  - target: Nodal Cilia Motility Failure at the Left-Right Organizer
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      Mns1-null mice display situs inversus, the organismal readout of failed nodal
      cilium function, and their tracheal motile cilia show the partial outer dynein
      arm loss that is the presumed proximate cause.
    limitations: >-
      Nodal cilium beating and nodal flow were not measured directly in this study;
      situs inversus and tracheal ciliary ultrastructure are used as proxies. The
      mouse also develops hydrocephalus, which has not been reported in
      MNS1-deficient humans.
    readouts:
    - name: Tracheal ciliary outer dynein arm content
      target: Nodal Cilia Motility Failure at the Left-Right Organizer
      direction: DECREASED
      interpretation: >-
        Partial loss of outer dynein arms from motile cilia is the ultrastructural
        readout supporting impaired ciliary beating in this model.
      evidence:
      - reference: PMID:22396656
        reference_title: >-
          MNS1 is essential for spermiogenesis and motile ciliary functions in
          mice.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: MNS1-deficient tracheal motile cilia lack some outer dynein arms in the axoneme.
        explanation: >-
          Reports the measured ultrastructural deficit, and notably that it is
          partial, matching the human finding.
    evidence:
    - reference: PMID:22396656
      reference_title: MNS1 is essential for spermiogenesis and motile ciliary functions in mice.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: In addition, MNS1-deficient mice display situs inversus and hydrocephalus.
      explanation: >-
        The laterality phenotype in the mouse null is the organismal evidence that
        this model is informative for the nodal-cilium node.

diagnosis:
- name: Molecular genetic testing
  description: >-
    Diagnosis rests on identification of biallelic loss-of-function MNS1 variants by
    exome, genome or motile-ciliopathy panel sequencing in an individual with a
    laterality defect, with or without male infertility. Because the airway
    phenotype is usually absent, MNS1 deficiency is frequently reached through
    genome-wide sequencing of a heterotaxy cohort rather than through a primary
    ciliary dyskinesia diagnostic pathway.
  evidence:
  - reference: PMID:39513328
    reference_title: Genetic Analysis of Heterotaxy in a Consanguineous Cohort.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our work demonstrates a relatively high yield of genetic testing in HTX in a
      consanguineous population with an enrichment of homozygous variants.
    explanation: >-
      Supports genome-wide molecular testing as the diagnostic route by which
      recessive heterotaxy genes including MNS1 are identified.
- name: Immunofluorescence analysis of ciliated cells
  description: >-
    Immunofluorescence staining of respiratory epithelial cells or spermatozoa
    demonstrates absence of MNS1 from the axoneme, and is used to confirm the
    functional consequence of candidate variants.
  evidence:
  - reference: PMID:38920647
    reference_title: >-
      Biallelic Variants in MNS1 Are Associated with Laterality Defects and
      Respiratory Involvement.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Accordingly, immunofluorescence analysis showed the absence of MNS1 from the
      respiratory epithelial cells of this individual.
    explanation: >-
      Demonstrates the use of immunofluorescence to confirm loss of the MNS1 protein
      in a patient sample.

treatments:
- name: Surgical management of congenital heart disease
  description: >-
    In individuals with true heterotaxy and complex congenital heart disease,
    staged cardiac surgical repair or palliation is the mainstay of management.
    There is no MNS1-directed or mechanism-targeted therapy; management is entirely
    supportive and directed at the individual anatomical and functional consequences
    of the laterality defect.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: surgical procedure
    term:
      id: NCIT:C15329
      label: Surgical Procedure
  target_phenotypes:
  - preferred_term: Complex congenital heart malformation
    term:
      id: HP:0001627
      label: Abnormal heart morphology
  notes: >-
    Deliberately carries no evidence item: no MNS1-specific management study or
    guideline exists. Recorded because omitting management entirely would
    misrepresent the clinical picture, but citing a paper that does not make this
    claim would be worse than citing none.
- name: Assisted reproduction (intracytoplasmic sperm injection)
  description: >-
    ICSI is the conventional approach to severe oligoasthenoteratozoospermia. In the
    single reported MNS1-deficient couple, three ICSI cycles all failed to achieve
    pregnancy, so ICSI should not be presented to affected men as reliably
    effective.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: intracytoplasmic sperm injection
    term:
      id: NCIT:C185482
      label: Intracytoplasmic Sperm Injection
  target_phenotypes:
  - preferred_term: Male infertility
    term:
      id: HP:0003251
      label: Male infertility
  target_mechanisms:
  - target: Oligoasthenoteratozoospermia and Male Infertility
    treatment_effect: BYPASSES
    description: >-
      ICSI does not correct the flagellar lesion. It circumvents the requirement
      for sperm motility and normal morphology by injecting a single spermatozoon
      directly into the oocyte, so it acts on the reproductive consequence rather
      than on any upstream mechanism node. In the one reported MNS1-deficient
      couple the bypass worked as far as fertilisation and cleavage but did not
      produce a pregnancy, so it is recorded as an incomplete bypass.
    evidence:
    - reference: PMID:33037173
      reference_title: >-
        A novel homozygous frameshift mutation in MNS1 associated with severe
        oligoasthenoteratozoospermia in humans.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        eight eggs were fertilized successfully (fertilization rate: 80%), and
        eight viable cleavage embryos were achieved, which suggests that normal
        embryos could be obtained using the spermatozoa with the MNS1 mutation
        during ICSI treatment
      explanation: >-
        Direct evidence that the gamete-intrinsic defect can be bypassed at
        fertilisation. Recorded as PARTIAL because the same cycle did not lead to
        pregnancy, so the bypass is demonstrated only up to the cleavage stage.
  evidence:
  - reference: PMID:33037173
    reference_title: >-
      A novel homozygous frameshift mutation in MNS1 associated with severe
      oligoasthenoteratozoospermia in humans.
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A total of three intracytoplasmic sperm injection cycles were carried out for
      the proband's wife, but they all failed to lead to a successful pregnancy.
    explanation: >-
      A negative therapeutic result: three ICSI cycles in the only reported
      MNS1-deficient couple did not achieve pregnancy. Recorded as REFUTE against
      the implicit claim that ICSI reliably rescues fertility in this disorder. This
      is a single couple, so it constrains rather than settles the question.

discussions:
- discussion_id: mns1_pcd_boundary
  kind: KNOWLEDGE_GAP
  attaches_to:
  - pathophysiology#Respiratory Ciliary Dysfunction
  prompt: >-
    Does biallelic MNS1 loss of function cause primary ciliary dyskinesia-grade
    airway disease on its own, or only a mild and variable respiratory phenotype
    that requires a second ciliary lesion to become clinically significant?
  rationale: >-
    The two strongest airway observations in MNS1 deficiency are confounded or
    isolated. In the index cohort, the one individual with recurrent respiratory
    infections and the informative distal ODA-docking ultrastructure also carried
    homozygous DNAH5 mutations, a well-established PCD gene, so her airway phenotype
    cannot be attributed to MNS1 alone. The later report of a pronounced respiratory
    phenotype rests on a single six-year-old girl, with two further individuals
    showing only a mild phenotype. ClinGen's Motile Ciliopathy Gene Curation Expert
    Panel classifies the MNS1-primary ciliary dyskinesia gene-disease relationship
    as Disputed. Resolving this matters clinically: it determines whether
    MNS1-deficient individuals need PCD surveillance (airway clearance, spirometry,
    imaging for bronchiectasis) or only laterality and fertility management.
  status: OPEN
  evidence:
  - reference: PMID:30148830
    reference_title: >-
      Homozygous loss-of-function mutations in MNS1 cause laterality defects and
      likely male infertility.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      a homozygous nonsense mutation p.Gln203* in one female with laterality defects
      and recurrent respiratory infections additionally carrying homozygous
      mutations in DNAH5
    explanation: >-
      Documents the DNAH5 co-mutation that confounds attribution of the airway
      phenotype to MNS1 in the index cohort.
  - reference: CGGV:assertion_255ba802-ece2-43c7-9089-6e54672b4f4a-2022-09-13T170000.000Z
    reference_title: MNS1 / primary ciliary dyskinesia (Disputed)
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      MNS1 | HGNC:29636 | primary ciliary dyskinesia | MONDO:0016575 | AR |
      Disputed
    explanation: >-
      An expert panel's formal classification of the MNS1-PCD relationship as
      Disputed, the current authoritative statement of this gap.
  proposed_experiments:
  - experiment_id: mns1_pcd_diagnostic_battery
    name: Systematic PCD diagnostic workup of an MNS1 cohort
    description: >-
      Apply the standard PCD diagnostic battery - nasal nitric oxide, high-speed
      video microscopy of ciliary beat frequency and waveform, transmission electron
      microscopy and air-liquid interface culture - to every reported MNS1-deficient
      individual without a second motile-ciliopathy gene lesion, and compare against
      genotype-matched DNAH5 controls. Only a systematic, second-gene-negative
      series can separate an MNS1-intrinsic airway phenotype from digenic or
      coincidental disease.
    decision_criterion: >-
      MNS1 is judged an independent cause of PCD-grade airway disease if
      second-gene-negative individuals show low nasal nitric oxide together with
      abnormal ciliary beat pattern in the majority of cases; it is judged
      insufficient alone if those individuals are indistinguishable from controls.
    would_support:
    - pathophysiology#Respiratory Ciliary Dysfunction

- discussion_id: mns1_hydrocephalus_model_mismatch
  kind: HUMAN_MODEL_MISMATCH
  attaches_to:
  - pathophysiology#Nodal Cilia Motility Failure at the Left-Right Organizer
  prompt: >-
    Mns1-null mice develop hydrocephalus, a canonical consequence of ependymal
    motile cilia dysfunction, yet hydrocephalus has not been reported in any
    MNS1-deficient human. Is the ependymal arm of MNS1 function genuinely absent in
    humans, or has it simply not been looked for?
  rationale: >-
    Ependymal cilia use the same axonemal machinery as nodal and respiratory cilia,
    so an MNS1-dependent ependymal phenotype is mechanistically expected. Its
    absence from the human literature could reflect a true species difference (mouse
    aqueductal geometry makes murine hydrocephalus far more sensitive to ciliary
    dysfunction than the human equivalent), ascertainment bias (affected individuals
    are ascertained through cardiology and fertility clinics, not neurology, and
    brain imaging is not routinely reported), or the small size of the published
    cohort. This is a model-fidelity question rather than a plain absence of
    evidence: the evidence exists in mouse and its translational validity to human
    disease is what is uncertain.
  status: OPEN
  evidence:
  - reference: PMID:22396656
    reference_title: MNS1 is essential for spermiogenesis and motile ciliary functions in mice.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: In addition, MNS1-deficient mice display situs inversus and hydrocephalus.
    explanation: The mouse phenotype that has no reported human counterpart.
  - reference: PMID:38920647
    reference_title: >-
      Biallelic Variants in MNS1 Are Associated with Laterality Defects and
      Respiratory Involvement.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Defects in motile cilia, termed motile ciliopathies, result in clinical
      manifestations affecting the respiratory and reproductive system, as well as
      laterality defects and hydrocephalus.
    explanation: >-
      Hydrocephalus is listed among the expected manifestations of motile
      ciliopathies in general, yet is not among the findings reported in this
      paper's five MNS1-deficient individuals.
  proposed_experiments:
  - experiment_id: mns1_prospective_neuroimaging
    name: Prospective neuroimaging of MNS1-deficient individuals
    description: >-
      Obtain brain MRI with ventricular volumetry in every genetically confirmed
      MNS1-deficient individual, and report ependymal ciliary function where
      post-mortem or surgical tissue is available. This distinguishes a genuine
      species difference from a reporting gap; a negative imaging series across the
      known cohort would itself be a substantive human result.
    decision_criterion: >-
      Ventriculomegaly in a meaningful fraction of the imaged cohort would establish
      the ependymal arm in humans; normal ventricular volumes across the full known
      cohort would establish the mouse hydrocephalus phenotype as species-specific.

- discussion_id: mns1_phenotype_expansion_uncertainty
  kind: KNOWLEDGE_GAP
  attaches_to:
  - pathophysiology#Randomization of Left-Right Axis Specification
  prompt: >-
    Are the non-ciliary features reported in individual MNS1 cases - severe myopia
    and oligodontia in one compound heterozygous woman, and a complex prenatal
    malformation syndrome in a sibling fetal pair - part of the MNS1 phenotype, or
    attributable to coincidental or second-locus variation?
  rationale: >-
    The report expanding the MNS1 phenotype describes features with no known
    connection to motile cilia. Critically, the two affected fetuses in that report
    carried homozygous GLDN variants in addition to their in-frame MNS1 deletion,
    so their malformation syndrome cannot be attributed to MNS1 without
    disentangling the two loci. Given that only a handful of individuals have ever
    been reported, single additional features carry disproportionate weight in
    shaping the perceived phenotype, and this entry deliberately does not curate
    them as MNS1 phenotypes.
  status: OPEN
  evidence:
  - reference: PMID:39233552
    reference_title: Expanding MNS1 Heterotaxy Phenotype.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The second and third patients were sibling fetuses with homozygous in-frame
      deletion variants in MNS1 and homozygous missense variants in GLDN.
    explanation: >-
      Documents the second-locus variant that confounds attribution of the fetal
      malformation syndrome to MNS1.
  - reference: PMID:39233552
    reference_title: Expanding MNS1 Heterotaxy Phenotype.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The first patient was a female presenting complete situs inversus and unusual
      symptoms, including severe myopia and dental agenesis of 10 permanent teeth.
    explanation: >-
      The authors themselves describe these features as unusual, marking them as
      unresolved rather than established components of the phenotype.

notes: >-
  Scope: this is a standalone Disease entry rather than a subtype of the existing
  Visceral_Heterotaxy entry (MONDO:0018677), which models heterotaxy as a
  genetically heterogeneous clinical class and carries no subtypes. HTX9 has its
  own MONDO term, its own OMIM phenotype number (618948), a single defined causal
  gene, and a phenotype - male infertility from flagellar assembly failure - that
  is not part of the umbrella entity at all. MONDO records HTX9 as is_a visceral
  heterotaxy, which the parents list reflects.

  No GeneReviews chapter exists for MNS1-related disease or for heterotaxy as of
  this curation, so the GeneReviews phenotype baseline step was not applicable.

  Named Entity Confusion preflight: MONDO:0030070 carries no textual definition, so
  identity was anchored on OMIM:618948 and on the MONDO RO:0004003 causal-gene
  relationship to HGNC:29636 (MNS1). All curated content is drawn from
  MNS1-specific primary literature. Content about other numbered heterotaxy loci
  (HTX1/ZIC3, HTX2/CFC1, HTX4/ACVR2B, HTX5/NODAL, HTX6/CFAP52) was deliberately
  excluded.

  A Falcon deep-research report was generated for this entry and then DISCARDED
  after `just preflight-dr ... MONDO:0030070` returned FAIL: the report never
  mentioned MNS1 and discussed MMP21 62 times, i.e. it had resolved "Visceral
  Heterotaxy 9" to MMP21-related heterotaxy 7 (MONDO:0014762, OMIM:616749). This
  is the canonical Named Entity Confusion failure mode for the numbered HTX
  series - the report was internally coherent, its citations resolved, and its
  quotes would have validated as exact substrings, so only the semantic gene check
  caught it. Per CLAUDE.md the report was discarded whole rather than
  cherry-picked, and is deliberately not committed under research/ so that a later
  curator cannot pick it up under its misleading filename. This entry is built
  entirely from PubMed-sourced MNS1 primary literature and the ClinGen structured
  record.

Visceral Heterotaxy 9

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