Delineation of the adult phenotype of Coffin-Siris syndrome in 35 individuals.

Coffin-Siris syndrome (CSS) is a rare multisystemic autosomal dominant disorder. Since 2012, alterations in genes of the SWI/SNF complex were identified as the molecular basis of CSS, studying largely pediatric cohorts. Therefore, there is a lack of information on the phenotype in adulthood, particularly on the clinical outcome in adulthood and associated risks. In an international collaborative effort, data from 35 individuals ≥ 18 years with a molecularly ascertained CSS diagnosis (variants in ARID1B, ARID2, SMARCA4, SMARCB1, SMARCC2, SMARCE1, SOX11, BICRA) using a comprehensive questionnaire was collected. Our results indicate that overweight and obesity are frequent in adults with CSS. Visual impairment, scoliosis, and behavioral anomalies are more prevalent than in published pediatric or mixed cohorts. Cognitive outcomes range from profound intellectual disability (ID) to low normal IQ, with most individuals having moderate ID. The present study describes the first exclusively adult cohort of CSS individuals. We were able to delineate some features of CSS that develop over time and have therefore been underrepresented in previously reported largely pediatric cohorts, and provide recommendations for follow-up.

Functional studies in yeast confirm the pathogenicity of a new GINS3 Meier-Gorlin syndrome variant.

Meier-Gorlin syndrome (MGORS) is an autosomal recessive disorder characterized by short stature, microtia, and patellar hypoplasia, and is caused by pathogenic variants of cellular factors involved in the initiation of DNA replication. We previously reported that biallelic variants in GINS3 leading to amino acid changes at position 24 (p.Asp24) cause MGORS. Here, we describe the phenotype of a new individual homozygous for the Asp24Asn variant. We also report the clinical characteristics of an individual harboring a novel homozygous GINS3 variant (Ile25Phe) and features suggestive of MGORS. Modification of the corresponding residue in yeast Psf3 (Val9Phe) compromised S phase progression compared to a humanized Psf3 Val9Ile variant. Expression of Psf3 Val9Phe in yeast also caused sensitivity to elevated temperature and the replicative stress-inducing drug hydroxyurea, confirming partial loss of function of this variant in vivo and allowing us to upgrade the classification of this variant. Taken together, these data validate the critical importance of the GINS DNA replication complex in the molecular etiology of MGORS.

Experience using singleton exome sequencing of probands as an approach to preconception carrier screening in consanguineous couples.

BACKGROUND: Consanguineous couples have an increased risk of severe diseases in offspring due to autosomal recessive disorders. Exome sequencing (ES) offers the possibility of extensive preconception carrier screening (PCS) in consanguineous couples who may be at risk of rare genetic disorders. METHODS: We retrospectively analysed ES data from 65 probands affected with rare genetic disorders born from consanguineous couples. We explored diagnostic yield and carrier status for recessive disorders. RESULTS: The overall diagnostic yield in a singleton approach was 53.8%, mostly recessive variants. In a hypothetical exome-based PCS, only 11.7% of these causative rare variants would have been missed in the filtering process. Carrier screening for recessive conditions allowed the identification of at least one additional pathogenic or likely pathogenic variant in 85.7% of the probands, being the majority with a gene carrier frequency <1 in 200. In addition, considering only clinically actionable conditions, we estimated that 12.3% of our close consanguineous couples may be at risk for an additional recessive disease. CONCLUSIONS: Our results demonstrate that ES outperforms panel-based screening in a PCS context in consanguineous couples and could potentially increase their reproductive autonomy and facilitate informed decision-making.

Clinical and psychological implications of secondary and incidental findings in cancer susceptibility genes after exome sequencing in patients with rare disorders.

BACKGROUND/OBJECTIVES: Exome sequencing may identify pathogenic variants unrelated with the purpose of the analysis. We investigated the frequency of secondary and incidental findings (SF/IF) in cancer susceptibility genes (CSG), their clinical actionability and the psychological impact in individuals with an SF/IF (cases) compared with individuals tested due to their cancer history (controls). METHODS: This study analysed 533 exomes ordered for non-cancer conditions. Medical records were reviewed for clinical actionability of SF/IF. Psychological impact was analysed using the Multidimensional Impact of Cancer Risk Assessment (MICRA) scale and compared between cases and controls with a propensity score weighting method. RESULTS: The frequency of SF/IF in CSG was 2.1% (95% CI 1.1% to 3.8%): three BRCA2, three PMS2, two SDHB, and one each in BRCA1, MLH1 and RAD51C. Among the relatives, 18 were carriers. Twenty enrolled for surveillance, and a neoplasm was diagnosed in 20%: three paragangliomas and one breast cancer. Cases presented higher MICRA mean scores than controls (21.3 vs 16.2 in MICRA total score, 6.3 vs 4.2 in the distress subscale, and 8.3 vs 6.6 in the uncertainty subscale; all p<0.001). CONCLUSION: SF/IF in CSG were identified in 2.1% of patients. Despite a numerically higher psychological impact, the identification of SF/IF allowed early detection and cancer prevention in families without cancer history.

Identification of two novel RRM2B variants associated with autosomal recessive progressive external ophthalmoplegia in a family with pseudodominant inheritance pattern.

RRM2B encodes the p53-inducible small subunit (p53R2) of ribonucleotide reductase, a key protein for mitochondrial DNA (mtDNA) synthesis. Pathogenic variants in this gene result in familial mitochondrial disease in adults and children, secondary to a maintenance disorder of mtDNA. This study describes two patients, mother and son, with early-onset chronic progressive external ophthalmoplegia (PEO). Skeletal muscle biopsy from the latter was examined: cytochrome c oxidase (COX)-negative fibres were shown, and molecular studies revealed multiple mtDNA deletions. A next-generation sequencing gene panel for nuclear-encoded mitochondrial maintenance genes identified two unreported heterozygous missense variants (c.514 G > A and c.682 G > A) in the clinically affected son. The clinically affected mother harboured the first variant in homozygous state, and the clinically unaffected father harboured the remaining variant in heterozygous state. In silico analyses predicted both variants as deleterious. Cell culture studies revealed that patients' skin fibroblasts, but not fibroblasts from healthy controls, responded to nucleoside supplementation with enhanced mtDNA repopulation, thus suggesting an in vitro functional difference in patients' cells. Our results support the pathogenicity of two novel RRM2B variants found in two patients with autosomal recessive PEO with multiple mtDNA deletions inherited with a pseudodominant pattern.

Chronic progressive external ophthalmoplegia plus syndrome due to homozygous missense variant in TOP3A gene.

Chronic progressive external ophthalmoplegia (CPEO) plus syndrome due to pathogenic biallelic variants in TOP3A gene has been described in only one single patient. We report two adult siblings with c.614A>G (p.Asp205Gly) homozygous missense variant in the TOP3A gene who had CPEO plus syndrome.

Evolution of clinical and radiological presentations of spondyloepimetaphyseal dysplasia, RPL13-related: Description of 11 further cases.

Spondyloepimetaphyseal dysplasia (SEMD), RPL13-related is caused by heterozygous variants in RPL13, which encodes the ribosomal protein eL13, a component of the 60S human ribosomal subunit. Here, we describe the clinical and radiological evolution of 11 individuals, 7 children and 4 adults, from 6 families. Some of the skeletal features improved during the course of this condition, whilst others worsened. We describe for the first time "corner fractures" as a feature of this dysplasia which as with other dysplasias disappear with age. In addition, we review the heights and skeletal anomalies of these reported here and previously in a total of 25 individuals from 15 families. In this study, six different RPL13 variants were identified, five of which were novel. All were located in the apparently hotspot region, located in intron 5 and exon 6. Splicing assays were performed for two of the three previously undescribed splicing variants. Until now, all splice variants have occurred in the intron 5 splice donor site, incorporating an additional 18 amino acids to the mutant protein. Here, we report the first variant in intron 5 splice acceptor site which generates two aberrant transcripts, deleting the first three and four amino acids encoded by exon 6. Thus, this study doubles the number of SEMD-RPL13-related cases and variants reported to date and describes unreported age-related clinical and radiological features.

A systematic study and literature review of parental somatic mosaicism of FBN1 pathogenic variants in Marfan syndrome.

BACKGROUND: A proportion of de novo variants in patients affected by genetic disorders, particularly those with autosomal dominant (AD) inheritance, could be the consequence of somatic mosaicism in one of the progenitors. There is growing evidence that germline and somatic mosaicism are more common and play a greater role in genetic disorders than previously acknowledged. In Marfan syndrome (MFS), caused by pathogenic variants in the fibrillin-1 gene (FBN1) gene, approximately 25% of the disease-causing variants are reported as de novo. Only a few cases of parental mosaicism have been reported in MFS. METHODS: Employing an amplicon-based deep sequencing (ADS) method, we carried out a systematic analysis of 60 parents of 30 FBN1 positive, consecutive patients with MFS with an apparently de novo pathogenic variant. RESULTS: Out of the 60 parents studied (30 families), the majority (n=51, 85%) had a systemic score of 0, seven had a score of 1 and two a score of 2, all due to minor criteria common in the normal population. We detected two families with somatic mosaicism in one of the progenitors, with a rate of 6.6% (2/30) of apparently de novo cases. CONCLUSIONS: The search for parental somatic mosaicism should be routinely implemented in de novo cases of MFS, to offer appropriate genetic and reproductive counselling as well as to reveal masked, isolated clinical signs of MFS in progenitors that may require specific follow-up.

Differences between genetic dilated cardiomyopathy and myocarditis in children presenting with severe cardiac dysfunction.

Acute myocarditis is an inflammatory disease of the myocardium, and it can present as severe heart failure in children. Differential diagnosis with genetic cardiomyopathy can be difficult. The objective of this study is to identify patterns of clinical presentation and to assess invasive and non-invasive measures to differentiate patients with acute myocarditis from patients with dilated genetic cardiomyopathy. We performed a retrospective descriptive study of all paediatric patients (0-16 years old) that presented with new-onset heart failure with left ventricle ejection fraction < 35% in whom we performed an endomyocardial biopsy (EMB) during the period from April 2007 to December 2020. The patients were classified into two groups: Group 1 included 18 patients with myocarditis. Group 2 included 9 patients with genetic cardiomyopathy. Findings favouring a diagnosis of myocarditis included a fulminant or acute presentation (77.8% vs 33.3%, p = 0.01), higher degree of cardiac enzyme elevation (p = 0.011), lower left ventricular dimension z-score (2.2 vs 5.4, p = 0.03) increase of ventricular wall thickness (88.8% vs 33.3%, p = 0.03) and oedema in the EMB. Seven (77.8%) patients with genetic cardiomyopathy had inflammation in the endomyocardial biopsy fulfilling the diagnostic criteria of inflammatory cardiomyopathy.Conclusion: Differentiating patients with a myocarditis from those with genetic cardiomyopathy can be challenging, even performing an EMB. Some patients with genetic cardiomyopathy fulfil the diagnostic criteria of inflammatory cardiomyopathy. Using invasive and non-invasive measures may be useful to develop a predictive model to differentiate myocarditis from genetic cardiomyopathy. What is Known: • Acute myocarditis could present with cardiogenic shock in paediatric patients. • Parvovirus B19 is the main cause of myocarditis in this population. What is New: • Current diagnostic criteria for myocarditis have limited use in paediatric patients presenting with new-onset heart failure. • Some patients with a genetic cardiomyopathy and a new-onset heart failure fulfill the diagnostic criteria of inflammatory cardiomyopathy.

Deep Molecular Characterization of Milder Spinal Muscular Atrophy Patients Carrying the c.859G>C Variant in SMN2

Spinal muscular atrophy (SMA) is a severe neuromuscular disorder caused by biallelic loss or pathogenic variants in the SMN1 gene. Copy number and modifier intragenic variants in SMN2, an almost identical paralog gene of SMN1, are known to influence the amount of complete SMN proteins. Therefore, SMN2 is considered the main phenotypic modifier of SMA, although genotype−phenotype correlation is not absolute. We present eleven unrelated SMA patients with milder phenotypes carrying the c.859G>C-positive modifier variant in SMN2. All were studied by a specific NGS method to allow a deep characterization of the entire SMN region. Analysis of two homozygous cases for the variant allowed us to identify a specific haplotype, Smn2-859C.1, in association with c.859G>C. Two other cases with the c.859G>C variant in their two SMN2 copies showed a second haplotype, Smn2-859C.2, in cis with Smn2-859C.1, assembling a more complex allele. We also identified a previously unreported variant in intron 2a exclusively linked to the Smn2-859C.1 haplotype (c.154-1141G>A), further suggesting that this region has been ancestrally conserved. The deep molecular characterization of SMN2 in our cohort highlights the importance of testing c.859G>C, as well as accurately assessing the SMN2 region in SMA patients to gain insight into the complex genotype−phenotype correlations and improve prognostic outcomes.

Assessment of frailty in elderly patients attending a multidisciplinary wound care centre: a cohort study.

BACKGROUND: The incidence of frailty and non-healing wounds increases with patients' age. Knowledge of the relationship between frailty and wound healing progress is greatly lacking. METHODS: The aim of this study is to characterize the degree of frailty in elderly patients attending a multidisciplinary wound care centres (MWCC). Additionally, we seek to assess the impact of frailty on the wound healing rate and wound healing time. An open cohort study was conducted on 51 consecutive patients aged > 70 years treated for wounds at an MWCC of an intermediate care hospital. The frailty score was determined according to the Frail-VIG index. Data were collected through patient questionnaires at the beginning of the study, and at 6 months or upon wound healing. Wounds were followed up every 2 weeks. To analyse the relationship between two variables was used the Chi-square test and Student's or the ANOVA model. The t-test for paired data was used to analyse the evolution of the frailty index during follow-up. RESULTS: A total of 51 consecutive patients were included (aged 81.1 ± 6.1 years). Frailty prevalence was 74.5% according to the Frail-VIG index (47.1% mildly frail, 19.6% moderately frail, and 7.8% severely frail). Wounds healed in 69.6% of cases at 6 months. The frailty index (FI) was higher in patients with non-healing wounds in comparison with patients with healing wounds (IF 0.31 ± 0.15 vs IF 0.24 ± 0.11, p = 0.043). A strong correlation between FI and wound healing results was observed in patients with non-venous ulcers (FI 0.37 ± 0.13 vs FI 0.27 ± 0.10, p = 0.015). However, no correlation was observed in patients with venous ulcers (FI 0.17 ± 0.09 vs FI 0.19 ± 0.09, p = 0.637). Wound healing rate is statically significantly higher in non-frail patients (8.9% wound reduction/day, P25-P75 3.34-18.3%/day;AQ6 p = 0.044) in comparison with frail patients (3.26% wound reduction/day, P25-P75 0.8-8.8%/day). CONCLUSION: Frailty is prevalent in elderly patients treated at an MWCC. Frailty degree is correlated with wound healing results and wound healing time.

Beyond the disease itself: A cross-cutting educational initiative for patients and families with rare diseases.

Rare diseases (RDs) as a whole affect a huge number of individuals although each specific condition comprises a low number of individuals. As a consequence, funds allocated to expand research to all conditions are often limited. Several initiatives have emerged to invest more resources for research in RDs, but patients express unmet needs regarding educational initiatives, awareness support, and psychosocial resources. We developed an educational training program in the format of weekly sessions covering basic medical scientific knowledge and psychosocial aspects of RDs. The aim of this initiative was to assess its overall impact regarding knowledge, psychological issues, and participant satisfaction. Items were evaluated through surveys before and after the sessions. Here, we report the experience and impact of two editions of this initiative with a total of 37 participants. Our results show improvements in knowledge and better management of the psychological impact. Moreover, participants were able to exchange experiences and concerns, most of which were shared even though the RDs were different. Overall, the program was evaluated by the participants as a highly beneficial experience and all of them were interested in attending advanced editions.

A toolkit for the quantitative evaluation of chronic wounds evolution for early detection of non-healing wounds.

BACKGROUND: Chronic wounds resulting from a number of conditions do not heal properly and can pose serious health problems. Beyond clinician visual inspection, an objective evaluation of the wound is required to assess wound evolution and the effectiveness of therapies. AIM: Our objective is to provide a methodology for the analysis of wound area vs. time for the early prediction of non-healing wounds evolution. METHODS: We propose a two-step approach consisting of: i) wound area quantification from planimetries and ii) classification of wound healing through the inference of characteristic parameters. For the first step, we describe a user-friendly software (Woundaries) to automatically calculate the wound area and other geometric parameters from hand-traced planimetries. For the second, we use a procedure for the objective classification of wound time evolution and the early assessment of treatment efficacy. The methodology was tested on simulations and retrospectively applied to data from 85 patients to compare the effect of a biological therapy with respect to general basic therapeutics. RESULTS: Woundaries provides measurements of wound surface equivalent to a validated device. The two-step methodology allows to determine if a wound is healing with high sensitivity, even with limited amount of data. Therefore, it allows the early assessment of the efficacy of a therapy. CONCLUSION: The performance of this methodology for the quantification and the objective evaluation of wound area evolution suggest it as a useful toolkit to assist clinicians in the early assessment of the efficacy of treatments, leading to a timely change of therapy.

Genetic factors contributing to autism spectrum disorder in Williams-Beuren syndrome.

BACKGROUND: The hallmark of the neurobehavioural phenotype of Williams-Beuren syndrome (WBS) is increased sociability and relatively preserved language skills, often described as opposite to autism spectrum disorders (ASD). However, the prevalence of ASD in WBS is 6-10 times higher than in the general population. We have investigated the genetic factors that could contribute to the ASD phenotype in individuals with WBS. METHODS: We studied four males and four females with WBS and a confirmed diagnosis of ASD by the Autism Diagnostic Interview-Revised. We performed a detailed molecular characterisation of the deletion and searched for genomic variants using exome sequencing. RESULTS: A de novo deletion of 1.55 Mb (6 cases) or 1.83 Mb (2 cases) at 7q11.23 was detected, being in 7/8 patients of paternal origin. No common breakpoint, deletion mechanism or size was found. Two cases were hemizygous for the rare T allele at rs12539160 in MLXIPL, previously associated with ASD. Inherited rare variants in ASD-related or functionally constrained genes and a de novo nonsense mutation in the UBR5 gene were identified in six cases, with higher burden in females compared with males (p=0.016). CONCLUSIONS: The increased susceptibility to ASD in patients with WBS might be due to additive effects of the common WBS deletion, inherited and de novo rare sequence variants in ASD-related genes elsewhere in the genome, with higher burden of deleterious mutations required for females, and possible hypomorphic variants in the hemizygous allele or cis-acting mechanisms on imprinting.

Signatures of Evolutionary Adaptation in Quantitative Trait Loci Influencing Trace Element Homeostasis in Liver.

Essential trace elements possess vital functions at molecular, cellular, and physiological levels in health and disease, and they are tightly regulated in the human body. In order to assess variability and potential adaptive evolution of trace element homeostasis, we quantified 18 trace elements in 150 liver samples, together with the expression levels of 90 genes and abundances of 40 proteins involved in their homeostasis. Additionally, we genotyped 169 single nucleotide polymorphism (SNPs) in the same sample set. We detected significant associations for 8 protein quantitative trait loci (pQTL), 10 expression quantitative trait loci (eQTLs), and 15 micronutrient quantitative trait loci (nutriQTL). Six of these exceeded the false discovery rate cutoff and were related to essential trace elements: 1) one pQTL for GPX2 (rs10133290); 2) two previously described eQTLs for HFE (rs12346) and SELO (rs4838862) expression; and 3) three nutriQTLs: The pathogenic C282Y mutation at HFE affecting iron (rs1800562), and two SNPs within several clustered metallothionein genes determining selenium concentration (rs1811322 and rs904773). Within the complete set of significant QTLs (which involved 30 SNPs and 20 gene regions), we identified 12 SNPs with extreme patterns of population differentiation (FST values in the top 5% percentile in at least one HapMap population pair) and significant evidence for selective sweeps involving QTLs at GPX1, SELENBP1, GPX3, SLC30A9, and SLC39A8. Overall, this detailed study of various molecular phenotypes illustrates the role of regulatory variants in explaining differences in trace element homeostasis among populations and in the human adaptive response to environmental pressures related to micronutrients.

How to Study the Location and Size of Rectal Tumors That Are Candidates for Local Surgery: Rigid Rectoscopy, Magnetic Resonance, Endorectal Ultrasound or Colonoscopy? An Interobservational Study.

1. BACKGROUND: Preoperative staging of rectal lesions for transanal endoscopic surgery (TES) comprises digital rectal examination, intraoperative rigid rectoscopy (IRR), endorectal ultrasound (EUS), colonoscopy and rectal magnetic resonance imaging (rMRI). The gold standard for topographic features is IRR. Are the results of the other tests sufficiently reliable to eliminate the need for IRR? rMRI is a key test in advanced rectal cancer and is not operator-dependent. Description of anatomical landmarks is variable. Can we rely on the information regarding topographic features provided by all radiologists? 2. MATERIALS AND METHODS: This is a concordance interobservational study involving four diagnostic tests of anatomical characteristics of rectal lesions (colonoscopy, EUS, rectal MRI and IRR), performed by four expert radiologists, regarding topographic rectal features with rMRI. 3. RESULTS: Fifty-five rectal tumors were operated on by using TES. The distance of the tumor from the anal verge, location by quadrants, size by quadrants and size of tumor were assessed (IRR as gold standard). For most of the tumors, the correlation between IRR and colonoscopy or EUS was very good (ICC > 0.75); the correlation between rMRI and IRR in respect of the size by quadrants (ICC = 0.092) and location by quadrants (ICC = 0.292) was weak. Topographic landmarks studied by the expert radiologists had an excellent correlation, except for distance from the peritoneal reflection to the anal verge (ICC = 0.606). 4. CONCLUSIONS: Anatomical description of rectal lesions by IRR, EUS, colonoscopy and rMRI is reliable. Topographic data obtained by EUS and colonoscopy can serve as a reference to avoid IRR. Determination of these topographic data by rMRI is less reliable. As performed by the expert radiologists, the anatomical study by rMRI is accurate and reproducible.

A novel FAM83G variant from palmoplantar keratoderma patient disrupts WNT signalling via loss of FAM83G-CK1α interaction.

Palmoplantar keratoderma (PPK) is a multi-faceted skin disorder characterized by the thickening of the epidermis and abrasions on the palms and soles of the feet. Among the genetic causes, biallelic pathogenic variants in the FAM83G gene have been associated with PPK in dogs and humans. Here, a novel homozygous variant (c.794G>C, p.Arg265Pro) in the FAM83G gene, identified by whole exome sequencing in a 60-year-old female patient with PPK, is reported. The patient exhibited alterations in the skin of both hands and feet, dystrophic nails, thin, curly and sparse hair, long upper eyelid eyelashes, and poor dental enamel. FAM83G activates WNT signalling through association with ser/thr protein kinase CK1α. When expressed in FAM83G-/- DLD1 colorectal cancer cells, the FAM83GR265P variant displayed poor stability, a loss of interaction with CK1α and attenuated WNT signalling response. These defects persisted in skin fibroblast cells derived from the patient. Our findings imply that the loss of FAM83G-CK1α interaction and subsequent attenuation of WNT signalling underlie the pathogenesis of PPK caused by the FAM83GR265P variant.

Complex SMN Hybrids Detected in a Cohort of 31 Patients With Spinal Muscular Atrophy.

Background and Objectives: Spinal muscular atrophy (SMA) is a recessive neuromuscular disorder caused by the loss or presence of point pathogenic variants in the SMN1 gene. The main positive modifier of the SMA phenotype is the number of copies of the SMN2 gene, a paralog of SMN1, which only produces around 10%-15% of functional SMN protein. The SMN2 copy number is inversely correlated with phenotype severity; however, discrepancies between the SMA type and the SMN2 copy number have been reported. The presence of SMN2-SMN1 hybrids has been proposed as a possible modifier of SMA disease. Methods: We studied 31 patients with SMA, followed at a single center and molecularly diagnosed by Multiplex Ligand-Dependent Probe Amplification (MLPA), with a specific next-generation sequencing protocol to investigate their SMN2 genes in depth. Hybrid characterization also included bioinformatics haplotype phasing and specific PCRs to resolve each SMN2-SMN1 hybrid structure. Results: We detected SMN2-SMN1 hybrid genes in 45.2% of the patients (14/31), the highest rate reported to date. This represents a total of 25 hybrid alleles, with 9 different structures, of which only 4 are detectable by MLPA. Of particular interest were 2 patients who presented 4 SMN2-SMN1 hybrid copies each and no pure SMN2 copies, an event reported here for the first time. No clear trend between the presence of hybrids and a milder phenotype was observed, although 5 of the patients with hybrid copies showed a better-than-expected phenotype. The higher hybrid detection rate in our cohort may be due to both the methodology applied, which allows an in-depth characterization of the SMN genes and the ethnicity of the patients, mainly of African origin. Discussion: Although hybrid genes have been proposed to be beneficial for patients with SMA, our work revealed great complexity and variability between hybrid structures; therefore, each hybrid structure should be studied independently to determine its contribution to the SMA phenotype. Large-scale studies are needed to gain a better understanding of the function and implications of SMN2-SMN1 hybrid copies, improving genotype-phenotype correlations and prediction of the evolution of patients with SMA.

Mutations in the U2 snRNA gene RNU2-2P cause a severe neurodevelopmental disorder with prominent epilepsy.

The major spliceosome comprises the five snRNAs U1, U2, U4, U5 and U6. We recently showed that mutations in RNU4- 2, which encodes U4 snRNA, cause one of the most prevalent monogenic neurodevelopmental disorders. Here, we report that recurrent germline mutations in RNU2-2P , a 191bp gene encoding U2 snRNA, are responsible for a related disorder. By genetic association, we implicated recurrent de novo single nucleotide mutations at nucleotide positions 4 and 35 of RNU2-2P among nine cases. We replicated this finding in six additional cases, bringing the total to 15. The disorder is characterized by intellectual disability, neurodevelopmental delay, autistic behavior, microcephaly, hypotonia, epilepsy and hyperventilation. All cases display a severe and complex seizure phenotype. Our findings cement the role of major spliceosomal snRNAs in the etiologies of neurodevelopmental disorders.