Clinical spectrum of individuals with pathogenic NF1 missense variants affecting p.Met1149, p.Arg1276, and p.Lys1423: genotype-phenotype study in neurofibromatosis type 1.

We report 281 individuals carrying a pathogenic recurrent NF1 missense variant at p.Met1149, p.Arg1276, or p.Lys1423, representing three nontruncating NF1 hotspots in the University of Alabama at Birmingham (UAB) cohort, together identified in 1.8% of unrelated NF1 individuals. About 25% (95% confidence interval: 20.5-31.2%) of individuals heterozygous for a pathogenic NF1 p.Met1149, p.Arg1276, or p.Lys1423 missense variant had a Noonan-like phenotype, which is significantly more compared with the "classic" NF1-affected cohorts (all p < .0001). Furthermore, p.Arg1276 and p.Lys1423 pathogenic missense variants were associated with a high prevalence of cardiovascular abnormalities, including pulmonic stenosis (all p < .0001), while p.Arg1276 variants had a high prevalence of symptomatic spinal neurofibromas (p < .0001) compared with "classic" NF1-affected cohorts. However, p.Met1149-positive individuals had a mild phenotype, characterized mainly by pigmentary manifestations without externally visible plexiform neurofibromas, symptomatic spinal neurofibromas or symptomatic optic pathway gliomas. As up to 0.4% of unrelated individuals in the UAB cohort carries a p.Met1149 missense variant, this finding will contribute to more accurate stratification of a significant number of NF1 individuals. Although clinically relevant genotype-phenotype correlations are rare in NF1, each affecting only a small percentage of individuals, together they impact counseling and management of a significant number of the NF1 population.

A novel RAB39B mutation and concurrent de novo NF1 mutation in a boy with neurofibromatosis type 1, intellectual disability, and autism: a case report.

BACKGROUND: Mutations in RAB39B at Xq28 causes a rare form of X-linked intellectual disability (ID) and Parkinson's disease. Neurofibromatosis type 1 (NF1) is caused by heterozygous mutations in NF1 occurring de novo in about 50% of cases, usually due to paternal gonadal mutations. This case report describes clinical and genetic findings in a boy with the occurrence of two distinct causative mutations in NF1 and RAB39B explaining the observed phenotype. CASE PRESENTATION: Here we report a 7-year-old boy with multiple café-au-lait macules (CALMs) and freckling, severe macrocephaly, peculiar facial gestalt, severe ID with absent speech, epilepsy, autistic traits, self-harming, and aggressiveness. Proband is an only child born to a father aged 47. Parents did not present signs of NF1, while a maternal uncle showed severe ID, epilepsy, and tremors.By RNA analysis of NF1, we identified a de novo splicing variant (NM_000267.3:c.6579+2T>C) in proband, which explained NF1 clinical features but not the severe ID, behavioral problems, and aggressiveness. Family history suggested an X-linked condition and massively parallel sequencing of X-exome identified a novel RAB39B mutation (NM_171998.2:c.436_447del) in proband, his mother, and affected maternal uncle, subsequently validated by Sanger sequencing in these and other family members. CONCLUSIONS: The case presented here highlights how concurrent genetic defects should be considered in NF1 patients when NF1 mutations cannot reasonably explain all the observed clinical features.

UBE2A deficiency in two siblings: A novel splicing variant inherited from a maternal germline mosaicism.

UBE2A deficiency is a syndromic condition of X-linked intellectual disability (ID) characterized by typical dysmorphic features that include synophrys, prominent supraorbital ridges, almond-shaped, and deep-set eyes, large ears, wide mouth, myxedematous appearance, hirsutism, micropenis, and onychodystrophy. To date, only seven familial UBE2A intragenic mutations and nine larger microdeletions encompassing UBE2A have been reported. Here, we describe two siblings with X-linked ID and typical clinical features of UBE2A deficiency caused by a novel hemizygous variant, identified by massively parallel sequencing of X-exome. The synonymous c.330G>A substitution in UBE2A modifies the last nucleotide of exon 5, causing the exon skipping and resulting in an out-of-frame transcript, likely encoding for a truncated form of the ubiquitin-conjugating enzyme E2 A. As confirmed by deep sequencing, the c.330G>A substitution in UBE2A was undetectable in genomic DNA from maternal blood cells, suggesting that the recurrent UBE2A deficiency observed in males of this family is caused by a maternal germline mosaicism.

Moyamoya syndrome in children with neurofibromatosis type 1: Italian-French experience.

Moyamoya syndrome (MMS) is the most common cerebral vasculopathy among children with neurofibromatosis type 1 (NF1). In this study, we clinically, radiologically, and genetically examined a cohort that was not previously described, comprising European children with NF1 and MMS. The NF1 genotyping had been registered. This study included 18 children. The mean age was 2.93 ± 3.03 years at the NF1 diagnosis and 7.43 ± 4.27 years at the MMS diagnosis. In seven patients, MMS was diagnosed before or at the same time as NF1. Neuroimaging was performed in 10 patients due to clinical symptoms, including headache (n = 6), cerebral infarction (n = 2), and complex partial seizures (n = 2). The remaining eight children (47%) had MMS diagnosed incidentally. Sixteen children were characterized molecularly. The features of MMS were similar between patients with and without NF1. Additionally, the NF1 phenotype and genotype were similar between children with and without MMS. Interestingly, three children experienced tumors with malignant histology or behavior. The presence of two first cousins in our cohort suggested that there may be potential genetic factors, not linked to NF1, with an additional role respect of NF1 might play a role in MMS pathogenesis. The incidental diagnosis of MMS, and the observation that, among children with NF1, those with MMS were clinically indistinguishable from those without MMS, suggested that it might be worthwhile to add an angiographic sequence to brain MRIs requested for children with NF1. A MMS diagnosis may assist in properly addressing an NF1 diagnosis in very young children who do not fulfill diagnostic criteria.

A novel diagnostic method to detect truncated neurofibromin in neurofibromatosis 1.

Neurofibromatosis type 1 (NF1) is an autosomal dominant genetic condition caused by dominant loss-of-function mutations of the tumor suppressor gene NF1 that encodes neurofibromin, a negative regulator of RAS activity. Mutation analysis of NF1 located at 17q11.2 has been hampered by the large size of the gene, the high rate of new mutations, the lack of mutational clustering, and the presence of several homologous loci. To date, about 80% of the reported NF1 mutations are predicted to result in protein truncation, but very few studies have correlated the causative NF1 mutation with its effect at the protein level. We evaluated a novel diagnostic method to detect truncated forms of neurofibromin in a large cohort of unrelated subjects suspected of having NF1, according to the NIH consensus criteria. Western blot analysis was carried out on protein extracts from patients' leukocytes to highlight the possible presence of altered neurofibromin as a result of mutations in NF1. Truncated neurofibromin was identified in 274/336 patients (81%), confirming the usefulness and reproducibility of the proposed diagnostic approach. Our methodology can be routinely applied in the diagnostic setting, thanks to its simplicity and reliability. Combined with molecular approaches, it may increase the accuracy and efficiency of NF1 genetic testing. We evaluated a novel diagnostic method to detect truncated forms of neurofibromin in patients fulfilling the clinical criteria for Neurofibromatosis 1. Western blot analysis identified truncated neurofibromin in 274/336 patients (81%). Our results indicate that the proposed technique is cheap and reliable, and could ideally be performed as a preliminary biochemical screening before molecular analysis of the NF1 gene.

LEOPARD syndrome: clinical dilemmas in differential diagnosis of RASopathies.

BACKGROUND: Diagnosis within RASopathies still represents a challenge. Nevertheless, many efforts have been made by clinicians to identify specific clinical features which might help in differentiating one disorder from another. Here, we describe a child initially diagnosed with Neurofibromatosis-Noonan syndrome. The follow-up of the proband, the clinical evaluation of his father together with a gene-by-gene testing approach led us to the proper diagnosis. CASE PRESENTATION: We report a 8-year-old male with multiple café-au-lait macules, several lentigines and dysmorphic features that suggest Noonan syndrome initially diagnosed with Neurofibromatosis-Noonan syndrome. However, after a few years of clinical and ophthalmological follow-up, the absence of typical features of Neurofibromatosis type 1 and the lack of NF1 mutation led us to reconsider the original diagnosis. A new examination of the patient and his similarly affected father, who was initially referred as healthy, led us to suspect LEOPARD syndrome, The diagnosis was then confirmed by the occurrence in both patients of a heterozygous mutation c.1403 C > T, p.(Thr468Met), of PTPN11. Subsequently, the proband was also found to have type-1 Arnold-Chiari malformation in association with syringomyelia. CONCLUSION: Our experience suggests that differential clinical diagnosis among RASopathies remains ambiguous and raises doubts on the current diagnostic clinical criteria. In some cases, genetic tests represent the only conclusive proof for a correct diagnosis and, consequently, for establishing individual prognosis and providing adequate follow-up. Thus, molecular testing represents an essential tool in differential diagnosis of RASophaties. This view is further strengthened by the increasing accessibility of new sequencing techniques.Finally, to our knowledge, the described case represents the third report of the occurrence of Arnold Chiari malformation and the second description of syringomyelia with LEOPARD syndrome.

Motor chip: a comparative genomic hybridization microarray for copy-number mutations in 245 neuromuscular disorders.

BACKGROUND: Array-based comparative genomic hybridization (aCGH) is a reference high-throughput technology for detecting large pathogenic or polymorphic copy-number variations in the human genome; however, a number of quantitative monogenic mutations, such as smaller heterozygous deletions or duplications, are usually missed in most disease genes when proper multiplex ligation-dependent probe assays are not performed. METHODS: We developed the Motor Chip, a customized CGH array with exonic coverage of 245 genes involved in neuromuscular disorders (NMDs), as well as 180 candidate disease genes. We analyzed DNA samples from 26 patients with known deletions or duplications in NMDs, 11 patients with partial molecular diagnoses, and 19 patients with a clinical diagnosis alone. RESULTS: The Motor Chip efficiently confirmed and refined the copy-number mutations in all of the characterized patients, even when only a single exon was involved. In noncharacterized or partially characterized patients, we found deletions in the SETX (senataxin), SGCG [sarcoglycan, gamma (35kDa dystrophin-associated glycoprotein)], and LAMA2 (laminin, alpha 2) genes, as well as duplications involving LAMA2 and the DYSF [dysferlin, limb girdle muscular dystrophy 2B (autosomal recessive)] locus. CONCLUSIONS: The combination of exon-specific gene coverage and optimized platform and probe selection makes the Motor Chip a complementary tool for molecular diagnosis and gene investigation in neuromuscular diseases.

Improving Copy Number Variant Detection from Sequencing Data with a Combination of Programs and a Predictive Model.

Bioinformatics tools for analyzing copy number variants (CNVs) from massively parallel sequencing (MPS) data are less well developed compared with other variant types. We present an efficient bioinformatics pipeline for CNV detection from gene panel MPS data in neuromuscular disorders. CNVs were generated in silico into samples sequenced with a previously published MPS gene panel. The in silico CNVs from these samples were analyzed with four programs having complementary CNV detection ranges: CoNIFER, XHMM, ExomeDepth, and CODEX. A logistic regression model was trained with the obtained set of in silico CNV detections to predict true-positive CNV detections among all CNV detections from samples. This model was validated using 66 control samples with a verified true-positive (n = 58) or false-positive (n = 8) CNV detection. Applying all four programs together provided more sensitive detection results with in silico CNVs than other program combinations or any program alone. Furthermore, a model with CNV detection-specific scores from all four programs as variables performed overall best in the validation. No single program could detect all CNV sizes and types equally or with enough accuracy. Therefore, a combination of carefully selected programs should be used to maximize detection accuracy. In addition, the detected CNVs should be reviewed with a statistical model to streamline and standardize the filtering of the detections for annotation.

Identification and Characterization of Splicing Defects by Single-Molecule Real-Time Sequencing Technology (PacBio).

Although DNA-sequencing is the most effective procedure to achieve a molecular diagnosis in genetic diseases, complementary RNA analyses are often required.Reverse-Transcription polymerase chain reaction (RT-PCR) is still a valuable option when the clinical phenotype and/or available DNA-test results address the diagnosis toward a gene of interest or when the splicing effect of a single variant needs to be assessed.We use Single-Molecule Real-Time sequencing to detect and characterize splicing defects and single nucleotide variants in well-known disease genes (DMD, NF1, TTN). After proper optimization, the procedure could be used in the diagnostic setting, simplifying the workflow of cDNA analysis.

The position of nonsense mutations can predict the phenotype severity: A survey on the DMD gene.

A nonsense mutation adds a premature stop signal that hinders any further translation of a protein-coding gene, usually resulting in a null allele. To investigate the possible exceptions, we used the DMD gene as an ideal model. First, because dystrophin absence causes Duchenne muscular dystrophy (DMD), while its reduction causes Becker muscular dystrophy (BMD). Second, the DMD gene is X-linked and there is no second allele that can interfere in males. Third, databases are accumulating reports on many mutations and phenotypic data. Finally, because DMD mutations may have important therapeutic implications. For our study, we analyzed large databases (LOVD, HGMD and ClinVar) and literature and revised critically all data, together with data from our internal patients. We totally collected 2593 patients. Positioning these mutations along the dystrophin transcript, we observed a nonrandom distribution of BMD-associated mutations within selected exons and concluded that the position can be predictive of the phenotype. Nonsense mutations always cause DMD when occurring at any point in fifty-one exons. In the remaining exons, we found milder BMD cases due to early 5' nonsense mutations, if reinitiation can occur, or due to late 3' nonsense when the shortened product retains functionality. In the central part of the gene, all mutations in some in-frame exons, such as in exons 25, 31, 37 and 38 cause BMD, while mutations in exons 30, 32, 34 and 36 cause DMD. This may have important implication in predicting the natural history and the efficacy of therapeutic use of drug-stimulated translational readthrough of premature termination codons, also considering the action of internal natural rescuers. More in general, our survey confirm that a nonsense mutation should be not necessarily classified as a null allele and this should be considered in genetic counselling.

Improved Criteria for the Classification of Titin Variants in Inherited Skeletal Myopathies.

BACKGROUND: Extensive genetic screening results in the identification of thousands of rare variants that are difficult to interpret. Because of its sheer size, rare variants in the titin gene (TTN) are detected frequently in any individual. Unambiguous interpretation of molecular findings is almost impossible in many patients with myopathies or cardiomyopathies. OBJECTIVE: To refine the current classification framework for TTN-associated skeletal muscle disorders and standardize the interpretation of TTN variants. METHODS: We used the guidelines issued by the American College of Medical Genetics and Genomics (ACMG) and the Association for Molecular Pathology (AMP) to re-analyze TTN genetic findings from our patient cohort. RESULTS: We identified in the classification guidelines three rules that are not applicable to titin-related skeletal muscle disorders; six rules that require disease-/gene-specific adjustments and four rules requiring quantitative thresholds for a proper use. In three cases, the rule strength need to be modified. CONCLUSIONS: We suggest adjustments are made to the guidelines. We provide frequency thresholds to facilitate filtering of candidate causative variants and guidance for the use and interpretation of functional data and co-segregation evidence. We expect that the variant classification framework for TTN-related skeletal muscle disorders will be further improved along with a better understanding of these diseases.

Congenital myopathy with hanging big toe due to homozygous myopalladin (MYPN) mutation.

BACKGROUND: Myopalladin (MYPN) is a component of the sarcomere that tethers nebulin in skeletal muscle and nebulette in cardiac muscle to alpha-actinin at the Z lines. Autosomal dominant MYPN mutations cause hypertrophic, dilated, or restrictive cardiomyopathy. Autosomal recessive MYPN mutations have been reported in only six families showing a mildly progressive nemaline or cap myopathy with cardiomyopathy in some patients. CASE PRESENTATION: A consanguineous family with congenital to adult-onset muscle weakness and hanging big toe was reported. Muscle biopsy showed minimal changes with internal nuclei, type 1 fiber predominance, and ultrastructural defects of Z line. Muscle CT imaging showed marked hypodensity of the sartorius bilaterally and MRI scattered abnormal high-intensity areas in the internal tongue muscle and in the posterior cervical muscles. Cardiac involvement was demonstrated by magnetic resonance imaging and late gadolinium enhancement. Whole exome sequencing analysis identified a homozygous loss of function single nucleotide deletion in the exon 11 of the MYPN gene in two siblings. Full-length MYPN protein was undetectable on immunoblotting, and on immunofluorescence, its localization at the Z line was missed. CONCLUSIONS: This report extends the phenotypic spectrum of recessive MYPN-related myopathies showing: (1) the two patients had hanging big toe and the oldest one developed spine and hand contractures, none of these signs observed in the previously reported patients, (2) specific ultrastructural changes consisting in Z line fragmentation, but (3) no nemaline or caps on muscle pathology.

Clinical and Genetic Findings in Children with Neurofibromatosis Type 1, Legius Syndrome, and Other Related Neurocutaneous Disorders.

Pigmentary manifestations can represent an early clinical sign in children affected by Neurofibromatosis type 1 (NF1), Legius syndrome, and other neurocutaneous disorders. The differential molecular diagnosis of these pathologies is a challenge that can now be met by combining next generation sequencing of target genes with concurrent second-level tests, such as multiplex ligation-dependent probe amplification and RNA analysis. We clinically and genetically investigated 281 patients, almost all pediatric cases, presenting with either NF1 (n = 150), only pigmentary features (café au lait macules with or without freckling; (n = 95), or clinical suspicion of other RASopathies or neurocutaneous disorders (n = 36). The causative variant was identified in 239 out of the 281 patients analyzed (85.1%), while 42 patients remained undiagnosed (14.9%). The NF1 and SPRED1 genes were mutated in 73.3% and 2.8% of cases, respectively. The remaining 8.9% carried mutations in different genes associated with other disorders. We achieved a molecular diagnosis in 69.5% of cases with only pigmentary manifestations, allowing a more appropriate clinical management of these patients. Our findings, together with the increasing availability and sharing of clinical and genetic data, will help to identify further novel genotype-phenotype associations that may have a positive impact on patient follow-up.

Assessment of de novo copy-number variations in Italian patients with schizophrenia: Detection of putative mutations involving regulatory enhancer elements.

OBJECTIVES: Variants appearing de novo in genes regulating key neurodevelopmental processes and/or in non-coding cis-regulatory elements (CREs), as enhancers, may increase the risk for schizophrenia. However, CREs involvement in schizophrenia needs to be explored more deeply. METHODS: We investigated de novo copy-number variations (CNVs) in the whole-genomic DNA obtained from 46 family trios of schizophrenia probands by using the Enhancer Chip, a customised array CGH able to investigate the whole genome with a 300-kb resolution, specific disease loci at a ten-fold higher resolution, and which was highly enriched in probes in more than 1,250 enhancer elements selected from Vista Enhancer Browser. RESULTS: In seven patients, we found de novo CNVs, two of which overlapped VISTA enhancer elements. De novo CNVs encompass genes (CNTNAP2, MAGI1, TSPAN7 and MET) involved in brain development, while that involving the enhancer element hs1043, also includes ZIC1, which plays a role in neural development and is responsible of behavioural abnormalities in Zic mutant mice. CONCLUSIONS: These findings provide further evidence for the involvement of de novo CNVs in the pathogenesis of schizophrenia and suggest that CNVs affecting regulatory enhancer elements could contribute to the genetic vulnerability to the disorder.

A Novel 12q13.2-q13.3 Microdeletion Syndrome With Combined Features of Diamond Blackfan Anemia, Pierre Robin Sequence and Klippel Feil Deformity.

Diamond-Blackfan anemia (DBA) is a rare congenital erythroid aplasia with a highly heterogeneous genetic background; it usually occurs in infancy. Approximately 30-40% of patients have other associated congenital anomalies; in particular, facial anomalies, such as cleft palate, are part of about 10% of the DBA clinical presentations. Pierre Robin sequence (PRS) is a heterogeneous condition, defined by the presence of the triad of glossoptosis, micrognathia and cleft palate; it occurs in 1/8500 to 1/14,000 births. Klippel Feil (KF) syndrome is a complex of both osseous and visceral anomalies, characterized mainly by congenital development defects of the cervical spine. We describe the case of a 22-years-old woman affected by DBA, carrying a de novo deletion about 500 Kb-long at 12q13.2-q13.3 that included RPS26 and, at least, others 25 flanking genes. The patient showed craniofacial anomalies due to PRS and suffered for KF deformities (type II). Computed Tomography study of cranio-cervical junction (CCJ) drew out severe bone malformations and congenital anomalies as atlanto-occipital assimilation (AOA), arcuate foramen and occipito-condylar hyperplasia. Foramen magnum was severely reduced. Atlanto-axial instability (AAI) was linked to atlanto-occipital assimilation, congenital vertebral fusion and occipito-condyle bone hyperplasia. Basilar invagination and platybasia were ruled out on CT and Magnetic Resonance Imaging (MRI) studies. Furthermore, the temporal Bone CT study showed anomalies of external auditory canals, absent mastoid pneumatization, chronic middle ear otitis and abnormal course of the facial nerve bones canal. The described phenotype might be related to the peculiar deletion affecting the patient, highlighting that genes involved in the in the breakdown of extracellular matrix (MMP19), in cell cycle regulation (CDK2), vesicular trafficking (RAB5B), in ribonucleoprotein complexes formation (ZC3H10) and muscles function (MYL6 and MYL6B) could be potentially related to bone-developmental disorders. Moreover, it points out that multiple associated ribosomal deficits might play a role in DBA-related phenotypes, considering the simultaneous deletion of three of them in the index case (RPS26, PA2G4 and RPL41), and it confirms the association among SLC39A5 functional disruption and severe myopia. This report highlights the need for a careful genetic evaluation and a detailed phenotype-genotype correlation in each complex malformative syndrome.

Whole exome sequencing identifies MRVI1 as a susceptibility gene for moyamoya syndrome in neurofibromatosis type 1.

BACKGROUND AND PURPOSE: Moyamoya angiopathy is a progressive cerebral vasculopathy. The p.R4810K substitution in RNF213 has previously been linked to moyamoya disease in Asian populations. When associated with other medical conditions, such as neurofibromatosis type 1, this vasculopathy is frequently reported as moyamoya syndrome. Intriguingly, most cases of moyamoya-complicated neurofibromatosis type 1 have been described in Caucasians, inverting the population ratio observed in Asians, although prevalence of neurofibromatosis type 1 is constant worldwide. Our aim was to investigate whether, among Caucasians, additive genetic factors may contribute to the occurrence of moyamoya in neurofibromatosis type 1. METHODS: Whole exome sequencing was carried out on an Italian family with moyamoya-complicated neurofibromatosis type 1 to identify putative genetic modifiers independent of the NF1 locus and potentially involved in moyamoya pathogenesis. Results were validated in an unrelated family of German ancestry. RESULTS: We identified the p.P186S substitution (rs35857561) in MRVI1 that segregated with moyamoya syndrome in both the Italian and German family. CONCLUSIONS: The rs35857561 polymorphism in MRVI1 may be a genetic susceptibility factor for moyamoya in European patients with neurofibromatosis type 1. MRVI1 is a functional partner of ITPR1, PRKG1 and GUCY1A3, which are involved in response to nitric oxide. Mutations in GUCY1A3 have been recently linked to a recessive syndromic form of moyamoya with esophageal achalasia.

Seizures in children with neurofibromatosis type 1: is neurofibromatosis type 1 enough?

BACKGROUND: Neurofibromatosis type 1 (NF1) is related to a generally increased prevalence of seizures. The mechanism underlying the increased predisposition to seizures has not been fully elucidated. The aim of the study was to evaluate the role of NF1 in seizures pathogenesis in a cohort of children with NF1 and seizures. METHODS: The medical records of 437 children (0-18 years old) with NF1 were reviewed. All children with at least one afebrile seizure were included. Demographic, clinical, neurological, NF1 mutation status, and EEG data were collected along with brain magnetic resonance imaging. Depending on etiology, structural seizures have been identified and were further classified as NF1 related or not. RESULTS: Nineteen patients (4.3%; 13 males) were included. NF1 was inherited in 7 (37.5%), with 3 maternal forms. Ten children with structural seizures were identified. Seven forms were identified someway related to NF1, two of which were associated to 17q11.2 microdeletion and hypoxic-ischemic encephalopathy. Any brain lesion that could explain seizures was found in nine patients, two third of these patients had a familiar history of epilepsy. CONCLUSIONS: Our results suggest seizures are more frequent in NF1 children (4.3%) than in general pediatric population (0.3-0.5%) and that are someway related to NF1 in half of patients. Facing seizures in NF1, the clinician should first exclude brain tumors but also other, and rarer NF1-related scenarios, such as hydrocephalous and vasculopathies. Children with non-structural seizures frequently had a family history of epilepsy, raising questions about the pathogenic role of NF1. They should be approached as for the general population.

Copy Number Variants Account for a Tiny Fraction of Undiagnosed Myopathic Patients.

Next-generation sequencing (NGS) technologies have led to an increase in the diagnosis of heterogeneous genetic conditions. However, over 50% of patients with a genetically inherited disease are still without a diagnosis. In these cases, different hypotheses are usually postulated, including variants in novel genes or elusive mutations. Although the impact of copy number variants (CNVs) in neuromuscular disorders has been largely ignored to date, missed CNVs are predicted to have a major role in disease causation as some very large genes, such as the dystrophin gene, have prone-to-deletion regions. Since muscle tissues express several large disease genes, the presence of elusive CNVs needs to be comprehensively assessed following an accurate and systematic approach. In this multicenter cohort study, we analyzed 234 undiagnosed myopathy patients using a custom array comparative genomic hybridization (CGH) that covers all muscle disease genes at high resolution. Twenty-two patients (9.4%) showed non-polymorphic CNVs. In 12 patients (5.1%), the identified CNVs were considered responsible for the observed phenotype. An additional ten patients (4.3%) presented candidate CNVs not yet proven to be causative. Our study indicates that deletions and duplications may account for 5⁻9% of genetically unsolved patients. This strongly suggests that other mechanisms of disease are yet to be discovered.

Targeted gene panel screening is an effective tool to identify undiagnosed late onset Pompe disease.

Mutations in the GAA gene may cause a late onset Pompe disease presenting with proximal weakness without the characteristic muscle pathology, and therefore a test for GAA activity is the first tier analysis in all undiagnosed patients with hyperCKemia and/or limb-girdle muscular weakness. By using MotorPlex, a targeted gene panel for next generation sequencing, we analyzed GAA and other muscle disease-genes in a large cohort of undiagnosed patients with suspected inherited skeletal muscle disorders (n = 504). In this cohort, 275 patients presented with limb-girdle phenotype and/or an isolated hyperCKemia. Mutational analysis identified GAA mutations in ten patients. Further seven affected relatives were identified by segregation studies. All the patients carried the common GAA mutation c.-32-13T >G and a second, previously reported mutation. In the subcohort of 275 patients with proximal muscle weakness and/or hyperCKemia, we identified late-onset Pompe disease in 10 patients. The clinical overlap between Pompe disease and LGMDs or other skeletal muscle disorders suggests that GAA and the genes causing a metabolic myopathy should be analyzed in all the gene panels used for testing neuromuscular patients. However, enzymatic tests are essential for the interpretation and validation of genetic results.