Homozygous Frameshift Variant Research Articles

Filippi syndrome: Three new families suggest that urinary system abnormalities may belong to clinical spectrum of the disease.

Filippi syndrome is a rare genetic disorder characterized by growth and neurodevelopmental delays, dysmorphism, and selective limb abnormalities. Although the syndrome was described approximately four decades ago, only a few families with molecularly confirmed diagnoses have been reported. In this article, we present three new patients of Filippi syndrome with unusual clinical and genetic aspects. These patients exhibited novel clinical features that have not previously been associated with Filippi syndrome, including renal hypoplasia/aplasia, renal cysts, renal cortical thinning, hypomelanotic, and hypermelanotic macules. All three patients had homozygous frameshift variants of the CKAP2L gene, specifically NM_152515.3: c.554_555del, c.981_982del, and c.1463_1467del, with the second being a novel variant. Given the limited number of reported Filippi syndrome patients to date and the ongoing discovery of new clinical aspects of the disease, exploring its potential connection with kidney and skin pigmentation abnormalities could be valuable for future research.

Novel MRI and histopathological findings in a young Bullmastiff cross dog with mitochondrial fission encephalopathy.

A 9-month-old male Bullmastiff cross dog was presented with a history of progressive proprioceptive ataxia and behavior changes. Neuroanatomical localization was multifocal with forebrain and vestibulo-cerebellum involvement. MRI identified moderate diffuse cerebral sulci widening, dilation of the ventricular system, and rounded, well-defined, bilaterally symmetrical T2W, FLAIR, and T2* hyperintense intra-axial lesions affecting the olivary nuclei. Histopathological examination was indicative of a primary mitochondrial disorder. This was confirmed following genetic analysis which identified mitochondrial fission encephalopathy with a homozygous frameshift variant in the MFF gene. This case report documents diagnostic imaging and histopathological findings not previously reported in dogs affected with mitochondrial fission encephalopathy, suggesting a different selective regional vulnerability of the neurons.

Discovery of a novel homozygous SOD1 truncating variant bolsters infantile SOD1 deficiency syndrome.

Superoxide dismutase 1 (SOD1) is an important antioxidant enzyme whose main function is to neutralise superoxide free radicals in the cytoplasm. Heterozygous variants in SOD1 are responsible for a substantial percentage of familial amyotrophic lateral sclerosis (ALS) cases. Recently, several reports have shown that biallelic loss of SOD1 function results in a novel phenotype called infantile SOD1 deficiency syndrome, which is consistent with a recessive pattern of inheritance and can be distinguished from typical (adult-onset) ALS. We documented detailed family histories and clinical data, followed by whole-exome sequencing and family co-segregation analysis through Sanger sequencing. To facilitate comparisons, relevant data from fifteen previously reported patients with SOD1-related neurodevelopmental disorders were included. This study presents a new Turkish family with two affected children exhibiting severe delayed motor development, infancy-onset loss of motor skills, axial hypotonia, tetraspasticity, and impaired cognitive functions. Genetic analysis revealed a novel homozygous frameshift variant in SOD1 (c.248dupG [p.Asp84Argfs*8]), with computational biochemical studies shedding light on the mechanistic aspects of SOD1 dysfunction. Our findings contribute an affirmative report of a fourth biallelic variant resulting in a severe clinical phenotype, reminiscent of those induced by previously identified homozygous loss-of-function SOD1 variants. This research not only advances our understanding of the pathogenesis of this debilitating neurological syndrome but also aligns with ongoing intensive efforts to comprehend and address SOD1-linked ALS.

A novel variant in NSUN2 causes intellectual disability in a Chinese family

NSUN2-intellectual disability syndrome, also known as intellectual disability type 5 (MRT5), is an autosomal recessive disorder that is characterized by intellectual disability (ID), postnatal growth retardation, dysmorphic facies, microcephaly, short stature, developmental delay, language impairment and other congenital abnormalities. The disease is caused by mutations in the NSUN2 gene, which encodes a tRNA cytosine methyltransferase that has an important role in spindle assembly during mitosis and chromosome segregation. In this study, we recruited a family that had two individuals with ID. Whole exome sequencing was performed to identify a homozygous frameshift variant (c.1171_1175delACCAT(p.Thr391fs*18*)) in NSUN2 (NM_017755.5) in the proband. The varint was confirmed as segregating in his affected brother and his parents by Sanger sequencing. The individuals that we described showed a similar dysmorphology profile to that associated with MRT5. To analyze the correlations between genotypes of NSUN2 and phenotypes of individuals with ID, we examined 17 variants and the associated phenotypes from 32 ID individuals in current and previous studies. We concluded that mutations in NSUN2 cause a wide range of phenotypic defects. Although some clinical manifestations were highly variable, the core phenotypes associated with NSUN2 mutations were dysmorphic facies, microcephaly, short stature, ID, growth restriction, language impairment, hypotonia and delayed puberty. Our study expands the genetic spectrum of NSUN2 mutations and helps to further define the genotype-phenotype correlations in MRT5.

Long-term course of a case with a novel homozygous kyphoscoliosis peptidase variant.

We herein report a case with a novel homozygous variant in the kyphoscoliosis peptidase (KY) gene. A 58-year-old Japanese female was referred to our hospital with a gait disturbance that gradually worsened after the age of 50. She had bilateral equinus foot deformity since early childhood. Neurological examination revealed moderate weakness of the neck, trunk, femoral, and brachial muscles, mild respiratory failure, and areflexia. Whole-exome sequencing revealed a novel homozygous frameshift variant of the KY gene, NM_178554.6:c.824del p.(Glu275Glyfs*53). Our case demonstrated that KY-associated neuromuscular disease can present with extremely slow progressive muscle weakness and respiratory failure over a long natural course.

Clinical and Molecular Characterization of a Novel Homozygous Frameshift Variant in AEBP1-Related Classical-like Ehlers Danlos Syndrome Type 2 with Comparison to Previously Reported Rare Cases.

Recently, an autosomal recessive subtype of connective tissue disorder within the spectrum of Ehlers-Danlos syndrome (EDS), named classical-like EDS type 2 (clEDS2), was identified. clEDS2 is associated with biallelic variants in the adipocyte enhancer binding protein 1 (AEBP1) gene, specifically, affecting its aortic carboxypeptidase-like protein (ACLP) isoform. We described the 15th patient (13th family) diagnosed with clEDS2. This patient presented with notable similarities in phenotype to the documented cases, along with additional characteristics such as significant prematurity and short stature. An EDS sequencing panel-based analysis revealed homozygous AEBP1: NM_001129.5:c.2923del, p.Ala975Profs*22 likely pathogenic variants, and maternally inherited heterozygous COL11A1: NM_001854.4:c.1160A>G, p.Lys387Arg variant of uncertain significance in our patient. Upon comprehensive review of all previously reported clEDS2 patients, our patient exhibited the following overlapping phenotypes, including cutaneous features: hyperextensibility, atrophic scars/delayed wound healing (100%), easy bruising (100%), excessive skin (93%); skeletal features: generalized joint hypermobility (93%), pes planus (93%), dislocation/subluxation (93%); and cardiovascular features (86%). Our patient did not display symptoms of the critical complications reported in a few individuals, including superior mesenteric artery aneurysms and ruptures, aortic root aneurysm/dissection, spontaneous pneumothoraxes, and bowel ruptures. Together, this case expands the genetic and clinical phenotypic spectrum of AEBP1-related clEDS2.

Biallelic loss-of-function variants of ZFTRAF1 cause neurodevelopmental disorder with microcephaly and hypotonia

PurposeNeurodevelopmental disorders exhibit clinical and genetic heterogeneity, ergo manifest dysfunction in components of diverse cellular pathways; the precise pathomechanism for the majority remains elusive. MethodsWe studied 5 affected individuals from 3 unrelated families manifesting global developmental delay, postnatal microcephaly, and hypotonia. We used exome sequencing and prioritized variants that were subsequently characterized using immunofluorescence, immunoblotting, pulldown assays, and RNA sequencing. ResultsWe identified biallelic variants in ZFTRAF1, encoding a protein of yet unknown function. Four affected individuals from 2 unrelated families segregated 2 homozygous frameshift variants in ZFTRAF1, whereas, in the third family, an intronic splice site variant was detected. We investigated ZFTRAF1 at the cellular level and signified it as a nucleocytoplasmic protein in different human cell lines. ZFTRAF1 was completely absent in the fibroblasts of 2 affected individuals. We also identified 110 interacting proteins enriched in mRNA processing and autophagy-related pathways. Based on profiling of autophagy markers, patient-derived fibroblasts show irregularities in the protein degradation process. ConclusionThus, our findings suggest that biallelic variants of ZFTRAF1 cause a severe neurodevelopmental disorder.

Co-occurring Usher syndrome Type 1 and Renal Failure.

To describe a patient with a rare co-occurrence of Usher syndrome type 1C (USH1C) and renal disease, suspected to be secondary to Alport syndrome. Case report and literature review of cases with Usher syndrome and renal failure. Clinical examination, color fundus photography, visual field tests, electroretinography and whole exome sequencing were used to diagnose and document the patient's clinical presentation. An 18-year-old female with known history of congenital hearing loss and chronic renal failure, presents with progressive night and peripheral visual impairment suspicious for an inherited retinal disease. Visual field testing, fundus exam and electroretinography findings supported the diagnosis of Usher syndrome. Whole exome sequencing (WES) identified a novel homozygous frameshift variant (c.238del) in USH1C. WES also identified a homozygous COL4A3 variant of unknown significance, which may be responsible for concomitant Alport syndrome. By presenting this rare case of co-occurring Usher syndrome Type 1 and renal failure, we highlight the importance of conducting further investigations that could reveal an additional underlying etiology when these entities are present.

Comprehensive functional characterization of a novel ANO6 variant in a new patient with Scott syndrome

BackgroundScott syndrome is a mild platelet-type bleeding disorder, first described in 1979, with only 3 unrelated families identified through defective phosphatidylserine (PS) exposure and confirmed by sequencing. The syndrome is distinguished by impaired surface exposure of procoagulant PS on platelets after stimulation. To date, platelet function and thrombin generation in this condition have not been extensively characterized. ObjectivesGenetic and functional studies were undertaken in a consanguineous family with a history of excessive bleeding of unknown cause. MethodsA targeted gene panel of known bleeding and platelet genes was used to identify possible genetic variants. Platelet phenotyping, flow adhesion, flow cytometry, whole blood and platelet-rich plasma thrombin generation, and specialized extracellular vesicle measurements were performed. ResultsWe detected a novel homozygous frameshift variant, c.1943del (p.Arg648Hisfs∗23), in ANO6 encoding Anoctamin 6, in a patient with a bleeding history but interestingly with normal ANO6 expression. Phenotyping of the patient’s platelets confirmed the absence of PS expression and procoagulant activity but also revealed other defects including reduced platelet δ granules, reduced ristocetin-mediated aggregation and secretion, and reduced P-selectin expression after stimulation. PS was absent on spread platelets, and thrombi formed over collagen at 1500/s. Reduced thrombin generation was observed in platelet-rich plasma and confirmed in whole blood using a new thrombin generation assay. ConclusionWe present a comprehensive report of a patient with Scott syndrome with a novel frameshift variant in AN06, which is associated with no platelet PS exposure and markedly reduced thrombin generation in whole blood, explaining the significant bleeding phenotype observed.

ST3GAL3 deficiency with autistic behavior: First description of frameshift variant and literature review

ST3GAL-III deficiency is an extremely rare genetic disease caused by pathogenic variants in the ST3GAL3 gene. There are two extremely rare disorders caused by homozygous mutations in the ST3GAL3 gene: developmental and epileptic encephalopathy 15 (MIM#615006) and intellectual developmental disorder, autosomal recessive 12 (MIM#611089). To date, no homozygous frameshift mutation in the ST3GAL3 gene has been identified that results in ST3GAL-III deficiency. The present study describes the first pathogenic homozygous frameshift variant (NM_174964.4:c.1113dup, p. Glu372ArgfsTer14) in the ST3GAL3 gene, which was identified by Whole-Exome sequencing and confirmed by Sanger sequencing. This novel mutation is responsible for developmental delay, speech impairment, epilepsy, hypotonia, intellectual disability, and behavioral issues in the proband. Eventually, we provide a case-based review of the clinical features associated with ST3GAL3 mutation. We compared our findings to previously reported cases, suggesting that developmental delay, speech impairment and intellectual disability are the main clinical features in ST3GAL3 deficient patients. Further studies would be beneficial to determine which genetic variants cause intellectual and behavioral problems, since they are highly diverse and poorly understood.

Brachyolmia, dental anomalies and short stature (DASS): Phenotype and genotype analyses of Egyptian and Pakistani patients

Brachyolmia is a heterogeneous group of developmental disorders characterized by a short trunk, short stature, scoliosis, and generalized platyspondyly without significant deformities in the long bones. DASS (Dental Abnormalities and Short Stature), caused by alterations in the LTBP3 gene, was previously considered as a subtype of brachyolmia.The present study investigated three unrelated consanguineous families (A, B, C) with Brachyolmia and DASS from Egypt and Pakistan. In our Egyptian patients, we also observed hearing impairment. Exome sequencing was performed to determine the genetic causes of the diverse clinical conditions in the patients. Exome sequencing identified a novel homozygous splice acceptor site variant (LTBP3:c.3629-1G > T; p. ?) responsible for DASS phenotypes and a known homozygous missense variant (CABP2: c.590T > C; p.Ile197Thr) causing hearing impairment in the Egyptian patients. In addition, two previously reported homozygous frameshift variants (LTBP3:c.132delG; p.Pro45Argfs*25) and (LTBP3:c.2216delG; p.Gly739Alafs*7) were identified in Pakistani patients.This study emphasizes the vital role of LTBP3 in the axial skeleton and tooth morphogenesis and expands the mutational spectrum of LTBP3. We are reporting LTBP3 variants in seven patients of three families, majorly causing brachyolmia with dental and cardiac anomalies. Skeletal assessment documented short webbed neck, broad chest, evidences of mild long bones involvement, short distal phalanges, pes planus and osteopenic bone texture as additional associated findings expanding the clinical phenotype of DASS. The current study reveals that the hearing impairment phenotype in Egyptian patients of family A has a separate transmission mechanism independent of LTBP3.

A novel SMOC1 pathogenic homozygous variant in a fetus with mesomelia of the lower limbs, micrognathia and hypertelorism and an incidental finding of CYP21A2-related congenital adrenal hyperplasia.

Trio exome sequencing was performed on a fetus with bilateral mesomelia of the lower limbs with significant angulation of the tibial bones, micrognathia and hypertelorism detected on ultrasound scan at 19+0weeks gestation. The couple is consanguineous. A homozygous pathogenic frameshift variant in the SMOC1 gene (c.339_340del p.(Phe114Cysfs*40)) was detected and both parents were shown to be heterozygous. Pathogenic variants in the SMOC1 gene are associated with microphthalmia with limb anomalies which multidisciplinary team discussion determined to be causal of the scan anomalies detected. The fetus was also a compound heterozygote for CYP21A2 pathogenic variants, confirming a second diagnosis of non-classical congenital adrenal hyperplasia, which was felt incidental to the scan findings. The risk that this couple's next pregnancy would be affected by either of these disorders is 1 in 4 (25%) and demonstrates the importance of genetic diagnoses for the family and implications for future pregnancies.

Two rare autosomal recessive neurological disorders identified by combined genetic approaches in a single consanguineous family with multiple offspring.

Neurodevelopmental disorders (NDDs) refer to a broad range of diseases including developmental delay, intellectual disability, epilepsy, autism spectrum disorders, and attention-deficit/hyperactivity disorder caused by dysfunctions in tightly controlled brain development. The genetic backgrounds of NDDs are quite heterogeneous; to date, recessive or dominant variations in numerous genes have been implicated. Herein, we present a large consanguineous family from Turkiye, who has been suffering from NDDs with two distinct clinical presentations. Combined in-depth genetic approaches led us to identify a homozygous frameshift variant in NALCN related to NDD and expansion of dodecamer repeat in CSTB related to Unverricht-Lundborg disease (ULD). Additionally, we sought to functionally analyze the NALCN variant in terms of mRNA expression level and current alteration. We have both detected a decrease in the level of premature stop codon-bearing mRNA possibly through nonsense-mediated mRNA decay mechanism and also an increased current in patch-clamp recordings for the expressed truncated protein. In conclusion, increased consanguinity may lead to the revealing of distinct rare neurogenetic diseases in a single family. Exome sequencing is generally considered the first-tier diagnostic test in individuals with NDD. Yet we underline the fact that customized approaches other than exome sequencing may be used as in the case of ULD to aid diagnosis and better genetic counseling.

Genetic insights into PHARC syndrome: identification of a novel frameshift mutation in ABHD12

BackgroundMutations in ABHD12 (OMIM: 613,599) are associated with polyneuropathy, hearing loss, ataxia, retinitis pigmentosa, and cataract (PHARC) syndrome (OMIM: 612674), which is a rare autosomal recessive neurodegenerative disease. PHARC syndrome is easily misdiagnosed as other neurologic disorders, such as retinitis pigmentosa, Charcot-Marie-Tooth disease, and Refsum disease, due to phenotype variability and slow progression. This paper presents a novel mutation in ABHD12 in two affected siblings with PHARC syndrome phenotypes. In addition, we summarize genotype-phenotype information of the previously reported patients with ABHD12 mutation.MethodsFollowing a thorough medical evaluation, whole-exome sequencing was done on the proband to look for potential genetic causes. This was followed by confirmation of identified variant in the proband and segregation analysis in the family by Sanger sequencing. The variants were interpreted based on the American College of Medical Genetics and Genomics (ACMG) guidelines.ResultsA novel pathogenic homozygous frameshift variant, NM_001042472.3:c.601dup, p.(Val201GlyfsTer4), was identified in exon 6 of ABHD12 (ACMG criteria: PVS1 and PM2, PM1, PM4, PP3, and PP4). Through Sanger sequencing, we showed that this variant is co-segregated with the disease in the family. Further medical evaluations confirmed the compatibility of the patients’ phenotype with PHARC syndrome.ConclusionsOur findings expand the spectrum of mutations in the ABHD12 and emphasize the significance of multidisciplinary diagnostic collaboration among clinicians and geneticists to solve the differential diagnosis of related disorders. Moreover, a summary based on mutations found so far in the ABHD12 gene did not suggest a clear genotype-phenotype correlation for PHARC syndrome.

Refining the phenotypic spectrum of CCDC88A-related PEHO-like syndrome.

Progressive encephalopathy with edema, hypsarrhythmia, and optic atrophy (PEHO) and PEHO-like syndromes are very rare infantile disorders characterized by profound intellectual disability, hypotonia, convulsions, optic, and progressive brain atrophy. Many causative genes for PEHO and PEHO-like syndromes have been identified including CCDC88A. So far, only five patients from two unrelated families with biallelic CCDC88A variants have been reported in the literature. Herein, we describe a new family from Egypt with a lethal epileptic encephalopathy. Our patient was the youngest child born to a highly consanguineous couple and had a family history of five deceased sibs with the same condition. She presented with postnatal microcephaly, poor visual responsiveness, and epilepsy. Her brain MRI showed abnormal cortical gyration with failure of opercularization of the insula, hypogenesis of corpus callosum, colpocephaly, reduced white matter, hypoplastic vermis, and brain stem. Whole exome sequencing identified a new homozygous frameshift variant in CCDC88A gene (c.1795_1798delACAA, p.Thr599ValfsTer4). Our study presents the third reported family with this extremely rare disorder. We also reviewed all described cases to better refine the phenotypic spectrum associated with biallelic loss of function variants in the CCDC88A gene.

Novel homozygous frameshift variant in the ATCAY gene in an Iranian patient with Cayman cerebellar ataxia; expanding the neuroimaging and clinical features: a case report

BackgroundPathogenic variants in the ATCAY gene are associated with a rare autosomal recessive disorder called Cayman cerebellar ataxia. Affected individuals display psychomotor retardation, cerebellar dysfunction, nystagmus, intention tremor, ataxic gait and dysarthric in some cases.Case presentationWhole exome sequencing was performed for a 21-month-old girl suffering from developmental delay specifically in motor and language aspects, hypotonia, nystagmus, pes planus and strabismus. The detected variant in the patient was confirmed by family segregation analysis by Sanger sequencing in both of her parents. Previously three homozygous variants in the ATCAY gene (missense, splice site and frameshift deletion) have been reported in patients with Cayman cerebellar ataxia. Here we report the fourth homozygous variant and the second homozygous frameshift deletion in this gene to be associated with autosomal recessive Cayman cerebellar ataxia.ConclusionThe identification of this novel homozygous frameshift deletion in the ATCAY gene expands our understanding of the genetic landscape underlying Cayman cerebellar ataxia. Furthermore, the occurrence of this variant in Iran, in addition to Pakistan, signifies the importance of considering genotypic and phenotypic factors beyond ethnicity when studying this disorder. These findings contribute to the ongoing efforts to unravel the molecular basis of Cayman cerebellar ataxia and improve diagnostic approaches and potential therapeutic interventions.

A homozygous frameshift variant in SYCP2 caused meiotic arrest and non-obstructive azoospermia.

Genetic causation for the majority of non-obstructive azoospermia (NOA) remains unclear. Mutations in synaptonemal complex (SC)-associated genes could cause meiotic arrest and NOA. Previous studies showed that heterozygous truncating variants in SYCP2 encoding a protein essential for SC formation, are associated with non-obstructive azoospermia and severe oligozoospermia. Herein, we showed a homozygous loss-of-function variant in SYCP2 (c.2689_2690insT) in an NOA-affected patient. And this variant was inherited from heterozygous parental carriers by natural reproduction. HE, IF, and meiotic chromosomal spread analyses demonstrated that spermatogenesis was arrested at the zygotene stage in the proband with NOA. Thus, this study revealed that SYCP2 associated with NOA segregates in an autosomal recessive inheritance pattern, rather than an autosomal dominant pattern. Furthermore, our study expanded the knowledge of variants in SYCP2 and provided new insight into understanding the genetic etiology of NOA.

A novel DOCK7 variant as a rare reason for epileptic encephalopathy, cortical blindness, dysmorphic features: A case report and brief review of the literature

Early infantile epileptic encephalopathy 23 (EIEE23; OMIM #615859) is a rare autosomal recessive disorder. It is characterized by refractory seizures, multifocal epileptic activity on electroencephalography, psychomotor development delay, dysmorphic facial features and cortical blindness/visual impairment. DOCK7 is involved in intracellular signaling networks and plays a role in axon formation and neuronal polarization. Function loss of this gene has previously been described in the molecular etiology of EIEE23. Here, we report a boy with a pathogenic novel variant in the DOCK7 gene presenting with, infantile-onset epileptic encephalopathy, severe neurodevelopmental delay, dysmorphic facial features, cortical blindness as well as previously unreported minor dental and extremity anomalies. Few cases with DOCK7 mutations have been reported in the literature. Due to its high genetic heterogeneity and scarcity, it is extremely important to report a novel and specific mutations and their associated clinical phenotypes. Whole exome sequencing revealed a novel pathogenic homozygous frameshift variant which has not been reported (c.5669dup (p.Cys1891ValfsTer2) mutation in the exon 44 of DOCK7).

Biallelic Variants in Seven Different Genes Associated with Clinically Suspected Bardet–Biedl Syndrome

Bardet-Biedl syndrome (BBS) is a rare clinically and genetically heterogeneous autosomal recessive multi-systemic disorder with 22 known genes. The primary clinical and diagnostic features include six different hallmarks, such as rod-cone dystrophy, learning difficulties, renal abnormalities, male hypogonadism, post-axial polydactyly, and obesity. Here, we report nine consanguineous families and a non-consanguineous family with several affected individuals presenting typical clinical features of BBS. In the present study, 10 BBS Pakistani families were subjected to whole exome sequencing (WES), which revealed novel/recurrent gene variants, including a homozygous nonsense mutation (c.94C>T; p.Gln32Ter) in the IFT27 (NM_006860.5) gene in family A, a homozygous nonsense mutation (c.160A>T; p.Lys54Ter) in the BBIP1 (NM_001195306.1) gene in family B, a homozygous nonsense variant (c.720C>A; p.Cys240Ter) in the WDPCP (NM_015910.7) in family C, a homozygous nonsense variant (c.505A>T; p.Lys169Ter) in the LZTFL1 (NM_020347.4) in family D, pathogenic homozygous 1 bp deletion (c.775delA; p.Thr259Leufs*21) in the MKKS/BBS5 (NM_170784.3) gene in family E, a pathogenic homozygous missense variant (c.1339G>A; p.Ala447Thr) in BBS1 (NM_024649.4) in families F and G, a pathogenic homozygous donor splice site variant (c.951+1G>A; p?) in BBS1 (NM_024649.4) in family H, a pathogenic bi-allelic nonsense variant in MKKS (NM_170784.3) (c.119C>G; p.Ser40*) in family I, and homozygous pathogenic frameshift variants (c.196delA; p.Arg66Glufs*12) in BBS5 (NM_152384.3) in family J. Our findings extend the mutation and phenotypic spectrum of four different types of ciliopathies causing BBS and also support the importance of these genes in the development of multi-systemic human genetic disorders.

Loss-of-function mutations in IQCN cause male infertility in humans and mice owing to total fertilization failure.

Fertilization failure is a significant manifestation of unexplained male infertility. Previous work has suggested a genetic origin. In this study, we report on a man with unexplained infertility from a large consanguineous marriage family. Whole-exome sequencing and Sanger sequencing identified a homozygous frameshift variation of the IQ motif containing N (IQCN; GenBank: NM_001145304.1; c.1061_1062delAT; p.Y354Sfs*13) in the proband and one of his two brothers, who also remained infertile. Analyses of spermatozoa by quantitative RT-PCR indicated that the level of IQCN mRNA was significantly reduced compared to fertile men and the protein could not be detected by western blotting and immunofluorescent staining in the proband. Immunofluorescent staining of spermatozoa from fertile men showed that IQCN was located in the acrosomal region and translocated to the equatorial segment after the acrosome reaction. The proband spermatozoa had abnormal morphology and function. Finally, the proband couple underwent IVF with donor sperm and a healthy baby was born. Furthermore, we developed an Iqcn-KO mouse model using the CRISPR/Cas9 technique. Sperm quality, except for sperm motility, and the fertility of male Iqcn-/- mice were consistent with those of the proband. In conclusion, the findings in humans and mice demonstrate that the homozygous frameshift variant of IQCN causes male infertility owing to autosomal-recessive fertilization failure.