Behavioral variant of frontotemporal dementia in carriers of biallelic TREM2 variants: cases study.

INTRODUCTION: First reports associated mutations in triggering receptors expressed on myeloid cells 2 (TREM2) with autosomal recessive Nasu-Hakola disease characterized by painful bone cysts and progressive presenile dementia with psychotic symptoms; however, recent TREM2 biallelic rare variants are suggested to be causative also for the behavioral variant of frontotemporal dementia (bvFTD) without bone involvement. MATERIAL AND METHODS: Clinical data of three unrelated bvFTD patients carrying TREM2 biallelic variants were evaluated. All patients underwent neurological, psychiatric, and cognitive evaluation and neuroimaging. A full neuropsychological assessment was performed in two cases. RESULTS: Two patients carried compound heterozygous TREM2 variants, p.R62C and p.T66M, and one carried the homozygous p.D87N variant. Based on all obtained clinical and neuroimaging data, a behavioral variant of frontotemporal dementia was diagnosed in all cases. Their clinical manifestation was typical with neuropsychiatric and cognitive features, without bone abnormalities. CONCLUSIONS: Despite all three subjects partially resembling clinical manifestations of Nasu-Hakola disease with TREM2 mutations, we reveal some distinct features, including age of onset, neuroimaging findings, or disease course.

Temporal restriction of Cas9 expression improves CRISPR-mediated deletion efficacy and fidelity.

Clinical application of CRISPR-Cas9 technology for large deletions of somatic mutations is inefficient, and methods to improve utility suffer from our inability to rapidly assess mono- vs. biallelic deletions. Here we establish a model system for investigating allelic heterogeneity at the single-cell level and identify indel scarring from non-simultaneous nuclease activity at gRNA cut sites as a major barrier to CRISPR-del efficacy both in vitro and in vivo. We show that non-simultaneous nuclease activity is partially prevented via restriction of CRISPR-Cas9 expression via inducible adeno-associated viruses (AAVs) or lipid nanoparticles (LNPs). Inducible AAV-based expression of CRISPR-del machinery significantly improved mono- and biallelic deletion frequency in vivo, supporting the use of the Xon cassette over traditional constitutively expressing AAV approaches. These data depicting improvements to deletions and insight into allelic heterogeneity after CRISPR-del will inform therapeutic approaches for phenotypes that require either large mono- or biallelic deletions, such as autosomal recessive diseases or where mutant allele-specific gRNAs are not readily available, or in situations where the targeted sequence for excision is located multiple times in a genome.

Investigation of the Genetic Determinants of Telangiectasia and Solid Organ Arteriovenous Malformation Formation in Hereditary Hemorrhagic Telangiectasia (HHT).

Telangiectases and arteriovenous malformations (AVMs) are the characteristic lesions of Hereditary Hemorrhagic Telangiectasia (HHT). Somatic second-hit loss-of-function variations in the HHT causative genes, ENG and ACVRL1, have been described in dermal telangiectasias. It is unclear if somatic second-hit mutations also cause the formation of AVMs and nasal telangiectasias in HHT. To investigate the genetic mechanism of AVM formation in HHT, we evaluated multiple affected tissues from fourteen individuals. DNA was extracted from fresh/frozen tissue of 15 nasal telangiectasia, 4 dermal telangiectasia, and 9 normal control tissue biopsies, from nine unrelated individuals with HHT. DNA from six formalin-fixed paraffin-embedded (FFPE) AVM tissues (brain, lung, liver, and gallbladder) from five individuals was evaluated. A 736 vascular malformation and cancer gene next-generation sequencing (NGS) panel was used to evaluate these tissues down to 1% somatic mosaicism. Somatic second-hit mutations were identified in three in four AVM biopsies (75%) or half of the FFPE (50%) samples, including the loss of heterozygosity in ENG in one brain AVM sample, in which the germline mutation occurred in a different allele than a nearby somatic mutation (both are loss-of-function mutations). Eight of nine (88.9%) patients in whom telangiectasia tissues were evaluated had a somatic mutation ranging from 0.68 to 1.96% in the same gene with the germline mutation. Six of fifteen (40%) nasal and two of four (50%) dermal telangiectasia had a detectable somatic second hit. Additional low-level somatic mutations in other genes were identified in several telangiectasias. This is the first report that nasal telangiectasias and solid organ AVMs in HHT are caused by very-low-level somatic biallelic second-hit mutations.

A mathematical description of nonself for biallelic genetic systems in pregnancy, transfusion, and transplantation.

A central issue in immunology is the immunological response against nonself. The prerequisite for a specific immunological response is the exposure to the immune system of a nonself antigen. Mathematical equations are presented, which define the fraction of all outcomes with a nonself allele in biallelic systems at the population level in pregnancy and transfusion/transplantation medicine. When designing assays, the mathematical descriptions can be used for estimating the number of genetic markers necessary to obtain a predetermined probability level in detecting nonself alleles of a given frequency. For instance, the equations can be helpful in the design of assays, where the nonself allele can be detected by analysis of cfDNA in plasma from pregnant women, to estimate fetal fraction or to monitor changes in cfDNA in plasma of transplantation patients. The equations give exact, quantitative descriptions of all nonself situations in pregnancy and transfusion/transplantation.

Patients with complex and very-early-onset ATL1-related spastic paraplegia offer insights on genotype/phenotype correlations and support for autosomal recessive forms of SPG3A.

Spastic paraplegia type 3A (SPG3A) is the second most common form of hereditary spastic paraplegia (HSP). This autosomal-dominant-inherited motor disorder is caused by heterozygous variants in the ATL1 gene which usually presents as a pure childhood-onset spastic paraplegia. Affected individuals present muscle weakness and spasticity in the lower limbs, with symptom onset in the first decade of life. Individuals with SPG3A typically present a slow progression and remain ambulatory throughout their life. Here we report three unrelated individuals presenting with very-early-onset (before 7 months) complex, and severe HSP phenotypes (axial hypotonia, spastic quadriplegia, dystonia, seizures and intellectual disability). For 2 of the 3 patients, these phenotypes led to the initial diagnosis of cerebral palsy (CP). These individuals carried novel ATL1 pathogenic variants (a de novo ATL1 missense p.(Lys406Glu), a homozygous frameshift p.(Arg403Glufs*3) and a homozygous missense variant (p.Tyr367His)). The parents carrying the heterozygous frameshift and missense variants were asymptomatic. Through these observations, we increase the knowledge on genotype-phenotype correlations in SPG3A and offer additional proof for possible autosomal recessive forms of SPG3A, while raising awareness on these exceptional phenotypes. Their ability to mimic CP also implies that genetic testing should be considered for patients with atypical forms of CP, given the implications for genetic counseling.

A family with nine siblings showing signs of Rothmund-Thomson syndrome with two being definitely diagnosed with the syndrome due to homozygous N-terminal mutation of RECQL4.

This study presents a family with nine children, two of them diagnosed with RTS2 using genetic testing. The other siblings show some of the RTS2 criteria and are suggestive of the syndrome. Such reports help physicians be more alert in dealing with cases of rare syndromes. Timely initiation of genetic counseling and testing once the first child was diagnosed with the syndrome could have prevented the birth of affected siblings by RTS2. Since RTS2 patients could have a severe clinical manifestation as osteosarcoma which probably leads to death at a young age, the importance of genetic testing is even more underlined.

Biallelic occult macular dystrophy.

PURPOSE: Occult macular dystrophy (OMD) is a cause of visual loss in young adults with a grossly normal fundus appearance. It is considered an autosomal dominant disorder, related to heterozygous pathogenic variants in the gene RP1L1. The purpose of this study is to report a biallelic form of the disease. RESULTS: A 29-year-old female had undergone neurological workup and ophthalmic examinations for transient visual loss in her left eye over the past two years but there was no definitive diagnosis. The best-corrected visual acuity was 20/30, 20/20. Indirect ophthalmoscopy with a 78D lens revealed subtle central retinal pigment epithelium mottling and optical coherence tomography confirmed subtle central thickening of the ellipsoid zone. Full-field electroretinography was normal, but pattern electroretinography showed decreased p50 responses. OMD was suspected. Retinal gene panel testing was significant only for a homozygous variant in RP1L1 (NM_178857.6: c.3571 G>T; p.Glu1191*). The parents and older brother were unavailable for segregation analysis. By history they did not have visual complaints other than a need for glasses. CONCLUSIONS: This report presents the clinical and genetic findings of a biallelic form of OMD associated with a novel pathogenic variant in RP1L1. It would be of interest to carefully assess macular function in heterozygotes with this variant.

Leukoencephalopathy with calcifications, developmental brain abnormalities and skeletal dysplasia due to homozygosity for a hypomorphic CSF1R variant: A report of three siblings.

We report three siblings homozygous for CSF1R variant c.1969 + 115_1969 + 116del to expand the phenotype of "brain abnormalities, neurodegeneration, and dysosteosclerosis" (BANDDOS) and discuss its link with "adult leukoencephalopathy with axonal spheroids and pigmented glia" (ALSP), caused by heterozygous CSF1R variants. We evaluated medical, radiological, and laboratory findings and reviewed the literature. Patients presented with developmental delay, therapy-resistant epilepsy, dysmorphic features, and skeletal abnormalities. Secondary neurological decline occurred from 23 years in sibling one and from 20 years in sibling two. Brain imaging revealed multifocal white matter abnormalities and calcifications during initial disease in siblings two and three. Developmental brain anomalies, seen in all three, were most severe in sibling two. During neurological decline in siblings one and two, the leukoencephalopathy was progressive and had the MRI appearance of ALSP. Skeletal survey revealed osteosclerosis, most severe in sibling three. Blood markers, monocytes, dendritic cell subsets, and T-cell proliferation capacity were normal. Literature review revealed variable initial disease and secondary neurological decline. BANDDOS presents with variable dysmorphic features, skeletal dysplasia, developmental delay, and epilepsy with on neuro-imaging developmental brain anomalies, multifocal white matter abnormalities, and calcifications. Secondary neurological decline occurs with a progressive leukoencephalopathy, in line with early onset ALSP. Despite the role of CSF1R signaling in myeloid development, immune deficiency is absent. Phenotype varies within families; skeletal and neurological manifestations may be disparate.

Therapy-related myeloid neoplasms with single-hit TP53 mutations share the clinical, molecular, and survival characteristics of their multi-hit counterparts.

Recent updates in the classification of myeloid neoplasms (MNs) recognize the poor prognostic impact of TP53 mutations, with particular emphasis on the TP53 allele status. Studies on the effect of TP53 allele status exclusively in therapy-related MNs (t-MNs) are lacking. We compared the clinicopathologic and survival characteristics of t-MNs with single-hit (SH) and multi-hit (MH) TP53 mutations. A total of 71 TP53-mutated t-MNs were included, including 56 (78.9%) MH and 15 (21.1%) SH. Both groups showed comparable genetic profiles with an excess of high-risk karyotypes and a paucity of other co-mutated genes. TP53 was the sole detectable mutation in 73.3% of SH and 75.0% of MH cases. The overall survival (OS) of SH TP53-mutated t-MNs was not significantly different from MH cases (median survival: 233 vs.273 days, p = 0.70). Our findings suggest that t-MNs with SH TP53 mutations share the poor prognostic and biologic profile of their MH counterparts.

Exome-wide evidence of compound heterozygous effects across common phenotypes in the UK Biobank.

The phenotypic impact of compound heterozygous (CH) variation has not been investigated at the population scale. We phased rare variants (MAF ∼0.001%) in the UK Biobank (UKBB) exome-sequencing data to characterize recessive effects in 175,587 individuals across 311 common diseases. A total of 6.5% of individuals carry putatively damaging CH variants, 90% of which are only identifiable upon phasing rare variants (MAF < 0.38%). We identify six recessive gene-trait associations (p < 1.68 × 10-7) after accounting for relatedness, polygenicity, nearby common variants, and rare variant burden. Of these, just one is discovered when considering homozygosity alone. Using longitudinal health records, we additionally identify and replicate a novel association between bi-allelic variation in ATP2C2 and an earlier age at onset of chronic obstructive pulmonary disease (COPD) (p < 3.58 × 10-8). Genetic phase contributes to disease risk for gene-trait pairs: ATP2C2-COPD (p = 0.000238), FLG-asthma (p = 0.00205), and USH2A-visual impairment (p = 0.0084). We demonstrate the power of phasing large-scale genetic cohorts to discover phenome-wide consequences of compound heterozygosity.

Genetic changes in the FH gene cause vagal paraganglioma.

Vagal paraganglioma (VPGL) is a rare neuroendocrine tumor that originates from the paraganglion associated with the vagus nerve. VPGLs present challenges in terms of diagnostics and treatment. VPGL can occur as a hereditary tumor and, like other head and neck paragangliomas, is most frequently associated with mutations in the SDHx genes. However, data regarding the genetics of VPGL are limited. Herein, we report a rare case of a 41-year-old woman with VPGL carrying a germline variant in the FH gene. Using whole-exome sequencing, a variant, FH p.S249R, was identified; no variants were found in other PPGL susceptibility and candidate genes. Loss of heterozygosity analysis revealed the loss of the wild-type allele of the FH gene in the tumor. The pathogenic effect of the p.S249R variant on FH activity was confirmed by immunohistochemistry for S-(2-succino)cysteine (2SC). Potentially deleterious somatic variants were found in three genes, SLC7A7, ZNF225, and MED23. The latter two encode transcriptional regulators that can impact gene expression deregulation and are involved in tumor development and progression. Moreover, FH-mutated VPGL was characterized by a molecular phenotype different from SDHx-mutated PPGLs. In conclusion, the association of genetic changes in the FH gene with the development of VPGL was demonstrated. The germline variant FH: p.S249R and somatic deletion of the second allele can lead to biallelic gene damage that promotes tumor initiation. These results expand the clinical and mutation spectra of FH-related disorders and improve our understanding of the molecular genetic mechanisms underlying the pathogenesis of VPGL.

Significant but partial lipoprotein lipase functional loss caused by a novel occurrence of rare LPL biallelic variants.

BACKGROUND: Lipoprotein lipase (LPL) plays a crucial role in triglyceride hydrolysis. Rare biallelic variants in the LPL gene leading to complete or near-complete loss of function cause autosomal recessive familial chylomicronemia syndrome. However, rare biallelic LPL variants resulting in significant but partial loss of function are rarely documented. This study reports a novel occurrence of such rare biallelic LPL variants in a Chinese patient with hypertriglyceridemia-induced acute pancreatitis (HTG-AP) during pregnancy and provides an in-depth functional characterization. METHODS: The complete coding sequences and adjacent intronic regions of the LPL, APOC2, APOA5, LMF1, and GPIHBP1 genes were analyzed by Sanger sequencing. The aim was to identify rare variants, including nonsense, frameshift, missense, small in-frame deletions or insertions, and canonical splice site mutations. The functional impact of identified LPL missense variants on protein expression, secretion, and activity was assessed in HEK293T cells through single and co-transfection experiments, with and without heparin treatment. RESULTS: Two rare LPL missense variants were identified in the patient: the previously reported c.809G > A (p.Arg270His) and a novel c.331G > C (p.Val111Leu). Genetic testing confirmed these variants were inherited biallelically. Functional analysis showed that the p.Arg270His variant resulted in a near-complete loss of LPL function due to effects on protein synthesis/stability, secretion, and enzymatic activity. In contrast, the p.Val111Leu variant retained approximately 32.3% of wild-type activity, without impacting protein synthesis, stability, or secretion. Co-transfection experiments indicated a combined activity level of 20.7%, suggesting no dominant negative interaction between the variants. The patient's post-heparin plasma LPL activity was about 35% of control levels. CONCLUSIONS: This study presents a novel case of partial but significant loss-of-function biallelic LPL variants in a patient with HTG-AP during pregnancy. Our findings enhance the understanding of the nuanced relationship between LPL genotypes and clinical phenotypes, highlighting the importance of residual LPL function in disease manifestation and severity. Additionally, our study underscores the challenges in classifying partial loss-of-function variants in classical Mendelian disease genes according to the American College of Medical Genetics and Genomics (ACMG)'s variant classification guidelines.

Recessive GNE Mutations in Korean Nonaka Distal Myopathy Patients with or without Peripheral Neuropathy.

Autosomal recessive Nonaka distal myopathy is a rare autosomal recessive genetic disease characterized by progressive degeneration of the distal muscles, causing muscle weakness and decreased grip strength. It is primarily associated with mutations in the GNE gene, which encodes a key enzyme of sialic acid biosynthesis (UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase). This study was performed to find GNE mutations in six independent distal myopathy patients with or without peripheral neuropathy using whole-exome sequencing (WES). In silico pathogenic prediction and simulation of 3D structural changes were performed for the mutant GNE proteins. As a result, we identified five pathogenic or likely pathogenic missense variants: c.86T>C (p.Met29Thr), c.527A>T (p.Asp176Val), c.782T>C (p.Met261Thr), c.1714G>C (p.Val572Leu), and c.1771G>A (p.Ala591Thr). Five affected individuals showed compound heterozygous mutations, while only one patient revealed a homozygous mutation. Two patients revealed unreported combinations of combined heterozygous mutations. We observed some specific clinical features, such as complex phenotypes of distal myopathy with distal hereditary peripheral neuropathy, an earlier onset of weakness in legs than that of hands, and clinical heterogeneity between two patients with the same set of compound heterozygous mutations. Our findings on these genetic causes expand the clinical spectrum associated with the GNE mutations and can help prepare therapeutic strategies.

Severe manifestation of Rauch-Azzarello syndrome associated with biallelic deletion of CTNND2.

CTNND2 encodes δ-catenin, a component of an adherens junction complex, and plays an important role in neuronal structure and function. To date, only heterozygous loss-of-function CTNND2 variants have been associated with mild neurodevelopmental delay and behavioral anomalies, a condition, which we named Rauch-Azzarello syndrome. Here, we report three siblings of a consanguineous family of Syrian descent with a homozygous deletion encompassing the last 19 exons of CTNND2 predicted to disrupt the transcript. All presented with severe neurodevelopmental delay with absent speech, profound motor delay, stereotypic behavior, microcephaly, short stature, muscular hypotonia with lower limb hypertonia, and variable eye anomalies. The parents and the fourth sibling were heterozygous carriers of the deletion and exhibited mild neurodevelopmental impairment resembling that of the previously described heterozygous individuals. The present study unveils a severe manifestation of CTNND2-associated Rauch-Azzarello syndrome attributed to biallelic loss-of-function aberrations, clinically distinct from the already described mild presentation of heterozygous individuals. Furthermore, we demonstrate novel clinical features in homozygous individuals that have not been reported in heterozygous cases to date.

The genetic landscape and phenotypic spectrum of GAA-FGF14 ataxia in China: a large cohort study.

BACKGROUND: An intronic GAA repeat expansion in FGF14 was recently identified as a cause of GAA-FGF14 ataxia. We aimed to characterise the frequency and phenotypic profile of GAA-FGF14 ataxia in a large Chinese ataxia cohort. METHODS: A total of 1216 patients that included 399 typical late-onset cerebellar ataxia (LOCA), 290 early-onset cerebellar ataxia (EOCA), and 527 multiple system atrophy with predominant cerebellar ataxia (MSA-c) were enrolled. Long-range and repeat-primed PCR were performed to screen for GAA expansions in FGF14. Targeted long-read and whole-genome sequencing were performed to determine repeat size and sequence configuration. A multi-modal study including clinical assessment, MRI, and neurofilament light chain was conducted for disease assessment. FINDINGS: 17 GAA-FGF14 positive patients with a (GAA)≥250 expansion (12 patients with a GAA-pure expansion, five patients with a (GAA)≥250-[(GAA)n (GCA)m]z expansion) and two possible patients with biallelic (GAA)202/222 alleles were identified. The clinical phenotypes of the 19 positive and possible positive cases covered LOCA phenotype, EOCA phenotype and MSA-c phenotype. Five of six patients with EOCA phenotype were found to have another genetic disorder. The NfL levels of patients with EOCA and MSA-c phenotypes were significantly higher than patients with LOCA phenotype and age-matched controls (p < 0.001). NfL levels of pre-ataxic GAA-FGF14 positive individuals were lower than pre-ataxic SCA3 (p < 0.001) and similar to controls. INTERPRETATION: The frequency of GAA-FGF14 expansion in a large Chinese LOCA cohort was low (1.3%). Biallelic (GAA)202/222 alleles and co-occurrence with other acquired or hereditary diseases may contribute to phenotypic variation and different progression. FUNDING: This study was funded by the National Key R&D Program of China (2021YFA0805200 to H.J.), the National Natural Science Foundation of China (81974176 and 82171254 to H.J.; 82371272 to Z.C.; 82301628 to L.W.; 82301438 to Z.L.; 82201411 to L.H.), the Innovation Research Group Project of Natural Science Foundation of Hunan Province (2020JJ1008 to H.J.), the Key Research and Development Program of Hunan Province (2020SK2064 to H.J.), the Innovative Research and Development Program of Development and Reform Commission of Hunan Province to H.J., the Natural Science Foundation of Hunan Province (2024JJ3050 to H.J.; 2022JJ20094 and 2021JJ40974 to Z.C.; 2022JJ40783 to L.H.; 2022JJ40703 to Z.L.), the Project Program of National Clinical Research Center for Geriatric Disorders (Xiangya Hospital, 2020LNJJ12 to H.J.), the Central South University Research Programme of Advanced Interdisciplinary Study (2023QYJC010 to H.J.) and the Science and Technology Innovation Program of Hunan Province (2022RC1027 to Z.C.). D.P. holds a Fellowship award from the Canadian Institutes of Health Research (CIHR).

Further delineation of Wiedemann-Rautenstrauch syndrome linked with POLR3A.

Wiedemann-Rautenstrauch Syndrome (WRS; MIM 264090) is an extremely rare and highly heterogeneous syndrome that is inherited in a recessive fashion. The patients have hallmark features such as prenatal and postnatal growth retardation, short stature, a progeroid appearance, hypotonia, facial dysmorphology, hypomyelination leukodystrophy, and mental impairment. Biallelic disease-causing variants in the RNA polymerase III subunit A (POLR3A) have been associated with WRS. Here, we report the first identified cases of WRS syndrome with novel phenotypes in three consanguineous families (two Omani and one Saudi) characterized by biallelic variants in POLR3A. Using whole-exome sequencing, we identified one novel homozygous missense variant (NM_007055: c.2456C>T; p. Pro819Leu) in two Omani families and one novel homozygous variant (c.1895G>T; p Cys632Phe) in Saudi family that segregates with the disease in the POLR3A gene. In silico homology modeling of wild-type and mutated proteins revealed a substantial change in the structure and stability of both proteins, demonstrating a possible effect on function. By identifying the homozygous variants in the exon 14 and 18 of the POLR3A gene, our findings will contribute to a better understanding of the phenotype-genotype relationship and molecular etiology of WRS syndrome.

Role of TRAK1 variants in epilepsy: genotype-phenotype analysis in a pediatric case of epilepsy with developmental disorder.

Purpose: The TRAK1 gene is mapped to chromosome 3p22.1 and encodes trafficking protein kinesin binding 1. The aim of this study was to investigate the genotype-phenotype of TRAK1-associated epilepsy. Methods: Trio-based whole-exome sequencing was performed on a cohort of 98 patients with epilepsy of unknown etiologies. Protein modeling and the VarCards database were used to predict the damaging effects of the variants. Detailed neurological phenotypes of all patients with epilepsy having TRAK1 variants were analyzed to assess the genotype-phenotype correlations. Results: A novel TRAK1 compound heterozygous variant comprising variant c.835C > T, p.Arg279Cys and variant c.2560A > C, p.Lys854Gln was identified in one pediatric patient. Protein modeling and VarCards database analyses revealed that the variants were damaging. The patient received a diagnosis of early infantile epileptic spasms with a developmental disorder; he became seizure-free through valproate and adrenocorticotropic hormone treatment. Further results for six variants in 12 patients with epilepsy indicated that biallelic TRAK1 variants (including homozygous or compound heterozygous variants) were associated with epilepsy with developmental disorders. Among these patients, eight (67%) had epileptic spasms and seven (58%) were intractable to anti-seizure medicines. Moreover, eight patients experienced refractory status epilepticus, of which seven (88%) died in early life. To our knowledge, this is the first reported case of epilepsy caused by TRAK1 compound heterozygous variants. Conclusion: Biallelic TRAK1 variants can cause epilepsy and developmental disorders. In these patients, seizures progress to status epilepticus, suggesting a high risk for poor outcomes and the requirement of early treatment.

Bi-allelic variants in DNAH3 cause male infertility with asthenoteratozoospermia in humans and mice.

STUDY QUESTION: Are there other pathogenic genes for asthenoteratozoospermia (AT)? SUMMARY ANSWER: DNAH3 is a novel candidate gene for AT in humans and mice. WHAT IS KNOWN ALREADY: AT is a major cause of male infertility. Several genes underlying AT have been reported; however, the genetic aetiology remains unknown in a majority of affected men. STUDY DESIGN SIZE DURATION: A total of 432 patients with AT were recruited in this study. DNAH3 mutations were identified by whole-exome sequencing (WES). Dnah3 knockout mice were generated using the genome editing tool. The morphology and motility of sperm from Dnah3 knockout mice were investigated. The entire study was conducted over 3 years. PARTICIPANTS/MATERIALS SETTING METHODS: WES was performed on 432 infertile patients with AT. In addition, two lines of Dnah3 knockout mice were generated. Haematoxylin and eosin (H&E) staining, transmission electron microscopy (TEM), immunostaining, and computer-aided sperm analysis (CASA) were performed to investigate the morphology and motility of the spermatozoa. ICSI was used to overcome the infertility of one patient and of the Dnah3 knockout mice. MAIN RESULTS AND THE ROLE OF CHANCE: DNAH3 biallelic variants were identified in three patients from three unrelated families. H&E staining revealed various morphological abnormalities in the flagella of sperm from the patients, and TEM and immunostaining further showed the loss of the central pair of microtubules, a dislocated mitochondrial sheath and fibrous sheath, as well as a partial absence of the inner dynein arms. In addition, the two Dnah3 knockout mouse lines demonstrated AT. One patient and the Dnah3 knockout mice showed good treatment outcomes after ICSI. LARGE SCALE DATA: N/A. LIMITATIONS REASONS FOR CAUTION: This is a preliminary report suggesting that defects in DNAH3 can lead to asthenoteratozoospermia in humans and mice. The pathogenic mechanism needs to be further examined in a future study. WIDER IMPLICATIONS OF THE FINDINGS: Our findings show that DNAH3 is a novel candidate gene for AT in humans and mice and provide crucial insights into the biological underpinnings of this disorder. The findings may also be beneficial for counselling affected individuals. STUDY FUNDING/COMPETING INTERESTS: This work was supported by grants from National Natural Science Foundation of China (82201773, 82101961, 82171608, 32322017, 82071697, and 81971447), National Key Research and Development Program of China (2022YFC2702604), Scientific Research Foundation of the Health Committee of Hunan Province (B202301039323, B202301039518), Hunan Provincial Natural Science Foundation (2023JJ30716), the Medical Innovation Project of Fujian Province (2020-CXB-051), the Science and Technology Project of Fujian Province (2023D017), China Postdoctoral Science Foundation (2022M711119), and Guilin technology project for people's benefit (20180106-4-7). The authors declare no competing interests.