Whole-exome sequencing improves the diagnosis and care of men with non-obstructive azoospermia.

Non-obstructive azoospermia (NOA) is a severe and frequent cause of male infertility, often treated by testicular sperm extraction followed by intracytoplasmic sperm injection. The aim of this study is to improve the genetic diagnosis of NOA, by identifying new genes involved in human NOA and to better assess the chances of successful sperm extraction according to the individual's genotype. Exome sequencing was performed on 96 NOA-affected individuals negative for routine genetic tests. Bioinformatics analysis was limited to a panel of 151 genes selected as known causal or candidate genes for NOA. Only highly deleterious homozygous or hemizygous variants were retained as candidates. A likely causal defect was identified in 16 genes in a total of 22 individuals (23%). Six genes had not been described in man (DDX25, HENMT1, MCMDC2, MSH5, REC8, TDRKH) and 10 were previously reported (C14orf39, DMC1, FANCM, GCNA, HFM1, MCM8, MEIOB, PDHA2, TDRD9, TERB1). Seven individuals had defects in genes from piwi or DNA repair pathways, three in genes involved in post-meiotic maturation, and 12 in meiotic processes. Interestingly, all individuals with defects in meiotic genes had an unsuccessful sperm retrieval, indicating that genetic diagnosis prior to TESE could help identify individuals with low or null chances of successful sperm retrieval and thus avoid unsuccessful surgeries.

Extending the clinical spectrum of X-linked Tonne-Kalscheuer syndrome (TOKAS): new insights from the fetal perspective.

INTRODUCTION: Tonne-Kalscheuer syndrome (TOKAS) is a recessive X-linked multiple congenital anomaly disorder caused by RLIM variations. Of the 41 patients reported, only 7 antenatal cases were described. METHOD: After the antenatal diagnosis of TOKAS by exome analysis in a family followed for over 35 years because of multiple congenital anomalies in five male fetuses, a call for collaboration was made, resulting in a cohort of 11 previously unpublished cases. RESULTS: We present a TOKAS antenatal cohort, describing 11 new cases in 6 French families. We report a high frequency of diaphragmatic hernia (9 of 11), differences in sex development (10 of 11) and various visceral malformations. We report some recurrent dysmorphic features, but also pontocerebellar hypoplasia, pre-auricular skin tags and olfactory bulb abnormalities previously unreported in the literature. Although no clear genotype-phenotype correlation has yet emerged, we show that a recurrent p.(Arg611Cys) variant accounts for 66% of fetal TOKAS cases. We also report two new likely pathogenic variants in RLIM, outside of the two previously known mutational hotspots. CONCLUSION: Overall, we present the first fetal cohort of TOKAS, describe the clinical features that made it a recognisable syndrome at fetopathological examination, and extend the phenotypical spectrum and the known genotype of this rare disorder.

An intermediate-effect size variant in UMOD confers risk for chronic kidney disease.

The kidney-specific gene UMOD encodes for uromodulin, the most abundant protein excreted in normal urine. Rare large-effect variants in UMOD cause autosomal dominant tubulointerstitial kidney disease (ADTKD), while common low-impact variants strongly associate with kidney function and the risk of chronic kidney disease (CKD) in the general population. It is unknown whether intermediate-effect variants in UMOD contribute to CKD. Here, candidate intermediate-effect UMOD variants were identified using large-population and ADTKD cohorts. Biological and phenotypical effects were investigated using cell models, in silico simulations, patient samples, and international databases and biobanks. Eight UMOD missense variants reported in ADTKD are present in the Genome Aggregation Database (gnomAD), with minor allele frequency (MAF) ranging from 10-5 to 10-3. Among them, the missense variant p.Thr62Pro is detected in ∼1/1,000 individuals of European ancestry, shows incomplete penetrance but a high genetic load in familial clusters of CKD, and is associated with kidney failure in the 100,000 Genomes Project (odds ratio [OR] = 3.99 [1.84 to 8.98]) and the UK Biobank (OR = 4.12 [1.32 to 12.85). Compared with canonical ADTKD mutations, the p.Thr62Pro carriers displayed reduced disease severity, with slower progression of CKD and an intermediate reduction of urinary uromodulin levels, in line with an intermediate trafficking defect in vitro and modest induction of endoplasmic reticulum (ER) stress. Identification of an intermediate-effect UMOD variant completes the spectrum of UMOD-associated kidney diseases and provides insights into the mechanisms of ADTKD and the genetic architecture of CKD.

Diagnostic Yield of Exome Sequencing in Early-Onset Hypertensive Nephropathy in Adults.

INTRODUCTION: Hypertensive nephrosclerosis (HN) ranks as one of the most frequent causes of chronic kidney disease (CKD), but its very existence has repeatedly been called into question, especially in young adults. Its diagnostic framework is established chiefly on non-specific clinical criteria, and its defining histopathological set of features is in fact shared by numerous other conditions. Genetic testing based on exome sequencing (ES) has emerged as a comprehensive tool to detect Mendelian diseases in timely fashion in nephrology, with a significant number of re-established diagnoses. The aim of this study was to investigate the diagnostic yield of ES in patients with a clinical diagnosis of hypertensive nephropathy. METHOD: Since September 2018, ES has been readily available as part of the routine diagnostic work-up in our institution. The indication of ES includes hypertensive nephropathy of early onset (i.e., <45 years old). We retrospectively collected the ES data performed in the context of hypertensive nephropathy in our institution between September 2018 and February 2021. RESULTS: A total of 128 patients were sequenced in the context of hypertensive nephropathy with early onset. The chief indications of ES were an early onset of CKD (47%), family history of kidney disease (8%), or both (18%). We detected diagnostic variants in 19 of the 128 patients (15%), encompassing a total of 13 different monogenic disorders. The diagnostic yield of ES was lower in patients of African ancestry (diagnostic yield of 7 vs. 30% in non-African ancestry patients, p < 0.001). CONCLUSIONS: The high diagnostic yield of ES (15%) in a population of patients thought to have HN casts further doubts on the validity of the existing diagnosis criteria, including histological criteria, supposed to characterize the condition. This was especially true in patients with no African ancestry, where ES positivity reached 30%.

Can we identify patients carrying targeted deleterious DPYD variants with plasma uracil and dihydrouracil? A GPCO-RNPGx retrospective analysis.

OBJECTIVES: Dihydropyrimidine dehydrogenase (DPD) deficiency is the main cause of severe fluoropyrimidine-related toxicities. The best strategy for identifying DPD-deficient patients is still not defined. The EMA recommends targeted DPYD genotyping or uracilemia (U) testing. We analyzed the concordance between both approaches. METHODS: This study included 19,376 consecutive French patients with pre-treatment plasma U, UH2 and targeted DPYD genotyping (*2A, *13, D949V, *7) analyzed at Eurofins Biomnis (2015-2022). RESULTS: Mean U was 9.9 ± 10.1 ng/mL (median 8.7, range 1.6-856). According to French recommendations, 7.3 % of patients were partially deficient (U 16-150 ng/mL) and 0.02 % completely deficient (U≥150 ng/mL). DPYD variant frequencies were *2A: 0.83 %, *13: 0.17 %, D949V: 1.16 %, *7: 0.05 % (2 homozygous patients with U at 22 and 856 ng/mL). Variant carriers exhibited higher U (median 13.8 vs. 8.6 ng/mL), and lower UH2/U (median 7.2 vs. 11.8) and UH2/U2 (median 0.54 vs. 1.37) relative to wild-type patients (p<0.00001). Sixty-six% of variant carriers exhibited uracilemia <16 ng/mL, challenging correct identification of DPD deficiency based on U. The sensitivity (% patients with a deficient phenotype among variant carriers) of U threshold at 16 ng/mL was 34 %. The best discriminant marker for identifying variant carriers was UH2/U2. UH2/U2<0.942 (29.7 % of patients) showed enhanced sensitivity (81 %) in identifying deleterious genotypes across different variants compared to 16 ng/mL U. CONCLUSIONS: These results reaffirm the poor concordance between DPD phenotyping and genotyping, suggesting that both approaches may be complementary and that targeted DPYD genotyping is not sufficiently reliable to identify all patients with complete deficiency.

Biallelic variants in NSUN6 cause an autosomal recessive neurodevelopmental disorder.

PURPOSE: 5-methylcytosine RNA modifications are driven by NSUN methyltransferases. Although variants in NSUN2 and NSUN3 were associated with neurodevelopmental diseases, the physiological role of NSUN6 modifications on transfer RNAs and messenger RNAs remained elusive. METHODS: We combined exome sequencing of consanguineous families with functional characterization to identify a new neurodevelopmental disorder gene. RESULTS: We identified 3 unrelated consanguineous families with deleterious homozygous variants in NSUN6. Two of these variants are predicted to be loss-of-function. One maps to the first exon and is predicted to lead to the absence of NSUN6 via nonsense-mediated decay, whereas we showed that the other maps to the last exon and encodes a protein that does not fold correctly. Likewise, we demonstrated that the missense variant identified in the third family has lost its enzymatic activity and is unable to bind the methyl donor S-adenosyl-L-methionine. The affected individuals present with developmental delay, intellectual disability, motor delay, and behavioral anomalies. Homozygous ablation of the NSUN6 ortholog in Drosophila led to locomotion and learning impairment. CONCLUSION: Our data provide evidence that biallelic pathogenic variants in NSUN6 cause one form of autosomal recessive intellectual disability, establishing another link between RNA modification and cognition.

Monoallelic Loss-of-Function IFT140 Pathogenic Variants Cause Autosomal Dominant Polycystic Kidney Disease: A Confirmatory Study With Suspicion of an Additional Cardiac Phenotype.

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited kidney disease. While biallelic variants affecting IFT140 are responsible for Mainzer-Saldino syndrome (characterized by severe ciliopathy causing skeletal abnormalities, kidney disease, and cysts), monoallelic loss-of-function (LoF) variants have been recently reported as an important cause of ADPKD beyond PKD1/2 genes. Herein, we report 6 non-family-related cases of monoallelic IFT140 LoF variants, identified from 1,340 exomes sequenced for nephrological indications in our local database. Every patient presented with polycystic kidney disease. Furthermore, the mother of a boy diagnosed with Mainzer-Saldino syndrome with a biallelic variant affecting IFT140 presented with several bilateral cysts, revealed after kidney imaging, and was found to carry a pathologic frameshift IFT140 variation. As well as this particular Mainzer-Saldino case, our 6 additional patients confirm that heterozygous IFT140 frameshift variants are responsible for the cystic phenotype and kidney failure. Interestingly, of the 6 patients, 2 also exhibited dilated cardiomyopathy, which was of unknown origin, as no genetic cause was found after exome sequencing analysis, suggesting a potential connection between IFT140 and heart disease.

Clinical and genetic spectra of 1550 index patients with hereditary spastic paraplegia.

Hereditary spastic paraplegia refers to rare genetic neurodevelopmental and/or neurodegenerative disorders in which spasticity due to length-dependent damage to the upper motor neuron is a core sign. Their high clinical and genetic heterogeneity makes their diagnosis challenging. Multigene panels allow a high-throughput targeted analysis of the increasing number of genes involved using next-generation sequencing. We report here the clinical and genetic results of 1550 index cases tested for variants in a panel of hereditary spastic paraplegia related genes analysed in routine diagnosis. A causative variant was found in 475 patients (30.7%) in 35/65 screened genes. SPAST and SPG7 were the most frequently mutated genes, representing 142 (9.2%) and 75 (4.8%) index cases of the whole series, respectively. KIF1A, ATL1, SPG11, KIF5A and REEP1 represented more than 1% (>17 cases) each. There were 661 causative variants (382 different ones) and 30 of them were structural variants. This large cohort allowed us to obtain an overview of the clinical and genetic spectrum of hereditary spastic paraplegia in clinical practice. Because of the wide phenotypic variability, there was no very specific sign that could predict the causative gene, but there were some constellations of symptoms that were found often related to specific subtypes. Finally, we confirmed the diagnostic effectiveness of a targeted sequencing panel as a first-line genetic test in hereditary spastic paraplegia. This is a pertinent strategy because of the relative frequency of several known genes (i.e. SPAST, KIF1A) and it allows identification of variants in the rarest involved genes and detection of structural rearrangements via coverage analysis, which is less efficient in exome datasets. It is crucial because these structural variants represent a significant proportion of the pathogenic hereditary spastic paraplegia variants (∼6% of patients), notably for SPAST and REEP1. In a subset of 42 index cases negative for the targeted multigene panel, subsequent whole-exome sequencing allowed a theoretical diagnosis yield of ∼50% to be reached. We then propose a two-step strategy combining the use of a panel of genes followed by whole-exome sequencing in negative cases.

Exome sequencing as a first-tier test for copy number variant detection: retrospective evaluation and prospective screening in 2418 cases.

BACKGROUND: Despite the availability of whole exome (WES) and genome sequencing (WGS), chromosomal microarray (CMA) remains the first-line diagnostic test in most rare disorders diagnostic workup, looking for copy number variations (CNVs), with a diagnostic yield of 10%-20%. The question of the equivalence of CMA and WES in CNV calling is an organisational and economic question, especially when ordering a WGS after a negative CMA and/or WES. METHODS: This study measures the equivalence between CMA and GATK4 exome sequencing depth of coverage method in detecting coding CNVs on a retrospective cohort of 615 unrelated individuals. A prospective detection of WES-CNV on a cohort of 2418 unrelated individuals, including the 615 individuals from the validation cohort, was performed. RESULTS: On the retrospective validation cohort, every CNV detectable by the method (ie, a CNV with at least one exon not in a dark zone) was accurately called (64/64 events). In the prospective cohort, 32 diagnoses were performed among the 2418 individuals with CNVs ranging from 704 bp to aneuploidy. An incidental finding was reported. The overall increase in diagnostic yield was of 1.7%, varying from 1.2% in individuals with multiple congenital anomalies to 1.9% in individuals with chronic kidney failure. CONCLUSION: Combining single-nucleotide variant (SNV) and CNV detection increases the suitability of exome sequencing as a first-tier diagnostic test for suspected rare Mendelian disorders. Before considering the prescription of a WGS after a negative WES, a careful reanalysis with updated CNV calling and SNV annotation should be considered.

Genome Alert!: A standardized procedure for genomic variant reinterpretation and automated gene-phenotype reassessment in clinical routine.

PURPOSE: Retrospective interpretation of sequenced data in light of the current literature is a major concern of the field. Such reinterpretation is manual and both human resources and variable operating procedures are the main bottlenecks. METHODS: Genome Alert! method automatically reports changes with potential clinical significance in variant classification between releases of the ClinVar database. Using ClinVar submissions across time, this method assigns validity category to gene-disease associations. RESULTS: Between July 2017 and December 2019, the retrospective analysis of ClinVar submissions revealed a monthly median of 1247 changes in variant classification with potential clinical significance and 23 new gene-disease associations. Re-examination of 4929 targeted sequencing files highlighted 45 changes in variant classification, and of these classifications, 89% were expert validated, leading to 4 additional diagnoses. Genome Alert! gene-disease association catalog provided 75 high-confidence associations not available in the OMIM morbid list; of which, 20% became available in OMIM morbid list For more than 356 negative exome sequencing data that were reannotated for variants in these 75 genes, this elective approach led to a new diagnosis. CONCLUSION: Genome Alert! (https://genomealert.univ-grenoble-alpes.fr/) enables systematic and reproducible reinterpretation of acquired sequencing data in a clinical routine with limited human resource effect.

CYP2U1 activity is altered by missense mutations in hereditary spastic paraplegia 56.

Hereditary spastic paraplegia (HSP) is an inherited disorder of the central nervous system mainly characterized by gradual spasticity and weakness of the lower limbs. SPG56 is a rare autosomal recessive early onset complicated form of HSP caused by mutations in CYP2U1. The CYP2U1 enzyme was shown to catalyze the hydroxylation of arachidonic acid. Here, we report two further SPG56 families carrying three novel CYP2U1 missense variants and the development of an in vitro biochemical assay to determine the pathogenicity of missense variants of uncertain clinical significance. We compared spectroscopic, enzymatic, and structural (from a 3D model) characteristics of the over expressed wild-type or mutated CYP2U1 in HEK293T cells. Our findings demonstrated that most of the tested missense variants in CYP2U1 were functionally inactive because of a loss of proper heme binding or destabilization of the protein structure. We also showed that functional data do not necessarily correlate with in silico predictions of variants pathogenicity, using different bioinformatic phenotype prediction tools. Our results therefore highlight the importance to use biological tools, such as the enzymatic test set up in this study, to evaluate the effects of newly identified variants in clinical settings.

A novel non sense mutation in WDR62 causes autosomal recessive primary microcephaly: a case report.

BACKGROUND: Autosomal recessive primary microcephaly (MCPH) is a rare genetically heterogeneous disorder of neurogenic brain development characterized by a reduced head circumference at birth with no remarkable anomalies of brain architecture and variable degrees of intellectual impairment. Clinical and genetic heterogeneity in genetic disorders represent a major diagnostic challenge. CASE PRESENTATION: Two patients, 11 and 9 years old, born from consanguineous parents, were referred to the department of medical genetics at the National Institute of Health in Rabat. The diagnosis of MCPH was made, based on reduced head circumference without brain architecture abnormalities. The two patients were subject to the whole-exome sequencing, which allowed to diagnose a novel homozygous mutation c.1027C > T; p.Gln343* in exon 8 of WDR62, a gene already known to be related to MCPH. Sanger sequencing confirmed the segregation of the mutation in the family. CONCLUSION: Our data expends the spectrum of mutations in WDR62 gene, proves the efficiency and cost-effectiveness of whole exome sequencing for the molecular diagnosis of genetically heterogeneous disorders such MCPH. Exome sequencing led to the rapid and cost-effective identification of a novel homozygous mutation in WDR62 gene, thereby facilitating genetic counseling.

KIF1C mutations in two families with hereditary spastic paraparesis and cerebellar dysfunction.

BACKGROUND: Hereditary spastic paraparesis (HSP) (syn. Hereditary spastic paraplegia, SPG) are a group of genetic disorders characterised by spasticity of the lower limbs due to pyramidal tract dysfunction. Nearly 60 disease loci have been identified, which include mutations in two genes (KIF5A and KIF1A) that encode motor proteins of the kinesin superfamily. Here we report a novel genetic defect in KIF1C of patients with spastic paraparesis and cerebellar dysfunction in two consanguineous families of Palestinian and Moroccan ancestry. METHODS AND RESULTS: We performed autozygosity mapping in a Palestinian and classic linkage analysis in a Moroccan family and found a locus on chromosome 17 that had previously been associated with spastic ataxia type 2 (SPAX2, OMIM %611302). Whole-exome sequencing revealed two homozygous mutations in KIF1C that were absent among controls: a nonsense mutation (c.2191C>T, p.Arg731*) that segregated with the disease phenotype in the Palestinian kindred resulted in the entire absence of KIF1C protein from the patient's fibroblasts, and a missense variant (c.505C>T, p.Arg169Trp) affecting a conserved amino acid of the motor domain that was found in the Moroccan kindred. CONCLUSIONS: Kinesin genes encode a family of cargo/motor proteins and are known to cause HSP if mutated. Here we identified nonsense and missense mutations in a further member of this protein family. The KIF1C mutation is associated with a HSP subtype (SPAX2/SAX2) that combines spastic paraplegia and weakness with cerebellar dysfunction.