Single Exon Deletions Research Articles

Beyond the panel: preconception screening in consanguineous couples using the TruSight One “clinical exome”

PurposeTo provide proof of concept by broadening preconception screening beyond targeted testing to inform reproductive risk in consanguineous couples. MethodsConsanguineous couples were screened for autosomal recessive and X-linked disorders using the TruSight One panel of 4,813 genes associated with human disease. ResultsWe recruited 22 couples, of whom 15 elected to have sequencing. We found four couples to be at risk of autosomal recessive disorders, including one with a child affected by Poretti–Boltshauser syndrome (a diagnosis not made prior to the study) and another previously known to carry a β-globin variant. Two couples were found to carry variants unrelated to known family history. These variants were in the genes C5orf42 (associated with Joubert syndrome and orofaciodigital syndrome) and GYS2 (associated with glycogen synthase deficiency). One known variant was not detected—a single exon deletion in FAM20C. We would not expect to identify this variant with the methodology employed. Of the four variants identified, only the β-globin variant would have been found using available commercial preconception screening panels. ConclusionPreconception screening of consanguineous couples for recessive and X-linked disorders using genomic sequencing is practicable, and is likely to detect many more at-risk couples than any targeted panel could achieve. A couples-based approach greatly reduces the associated analysis and counselling burden.

886: Detection of copy-number variants in expanded carrier screening maximizes identification of cystic fibrosis carriers

Cystic fibrosis is one of the most common autosomal recessive conditions. Medical-society guidelines recommend routine carrier screening for cystic fibrosis via targeted genotyping of 23 frequent single-nucleotide variants (SNVs) and short insertions or deletions (indels) in the CFTR gene. Screening for copy-number variants (CNVs) is recommended only when a reproductive partner is a known carrier. Here we assess the performance and clinical impact of routinely screening for SNVs, indels, and CNVs in a next-generation sequencing (NGS)-based expanded carrier screen (ECS). Pathogenic variants in CFTR from 103,718 patients were discovered via a validated NGS-based ECS. A custom algorithm identified CNVs via relative deviations in NGS read depth. Approximate CNV breakpoints were inferred from the NGS-depth profile. Positive CNVs were orthogonally assessed via multiplex ligation-dependent probe amplification (MLPA). CFTR CNV sensitivity was explored across a range of length scales via in silico simulations. Among carriers of cystic fibrosis, 98.7% had pathogenic SNVs or indels in the CFTR gene (79% had one of the 23 common variants), and the remaining 1.3% harbored a pathogenic CNV spanning at least one exon. In total, we observed 25 unique CNVs with a diversity of breakpoints, suggesting that algorithms must be configured to detect novel CNVs. Further, single-exon deletions were observed for seven different CFTR exons; analysis of confidence scores for these empirical deletions—coupled with extensive simulations—demonstrated that the bioinformatics pipeline was both accurate and robust, even for short CNVs. All CNVs identified via NGS were confirmed via MLPA. CNV detection maximizes identification of cystic fibrosis carriers and can be applied to all patients undergoing an NGS-based ECS test validated to detect these complicated variants. Clinical guidelines recommending screening of only the 23 most frequent variants miss critical identification of carriers and should be revisited.

Mutation analysis and prenatal diagnosis for 50 pedigrees affected with Duchenne/Becker muscular dystrophy

To establish individualized prenatal diagnosis program for families affected with Duchenne/Becker muscular dystrophy (DMD/BMD) and different clinical background using a variety of methods. Multiplex ligation-dependent probe amplification (MLPA) was performed on 50 patients suspected for DMD/BMD. For single exon deletions of the DMD gene, PCR was used for validating the results. For those without any deletion or duplication, Sanger sequencing was used to screen for DMD gene mutations in the children and their mothers. Prenatal genetic testing was provided to female carriers using chorionic villus, amniocentesis or cord blood samples. To ensure the accuracy of diagnosis, all prenatal specimens were also subjected to linkage analysis. Among the 50 patients with DMD/BMD, 23 harbored large deletions, 11 only had single exon deletions, 10 harbored duplications, and 5 had small scare mutations. No mutation was detected in one family. For 37 women undergoing prenatal diagnosis, 10 fetuses were identified as affected males, 6 were female carriers, while 21 were not found to carry any mutation. Testing of creatine kinase was consistent with the results of prenatal diagnosis. For a patient harboring exon 51 deletion, the same mutation was found in a fetus but not in their mother. The proband and fetus had inherited the same haplotype, which suggested that the mother probably has germline mosaicism for the mutation. Application of individualized methods for analyzing pregnant women with different clinical background can minimize the risk for giving birth to further children affected with DMD/BMD.

A Hemizygous Deletion Within the PGK1 Gene in Males with PGK1 Deficiency.

Phosphoglycerate kinase-1 (PGK1) deficiency is a rare X-linked disorder caused by pathogenic variants in the PGK1 gene. Complete loss-of-function variants have not been reported in this gene, indicating that residual enzyme function is critical for viability in males. Therefore, copy number variants (CNVs) that include single exon or multiple exon deletions or duplications are generally not expected in individuals with PGK1 deficiency. Here we describe a 64-year-old male presenting with a family history (three additional affected males) and a personal history of childhood-onset metabolic myopathy that involves episodes of muscle pain, stiffness after activity, exercise intolerance, and myoglobinuria after exertion. Biochemical analysis on a muscle biopsy indicated significantly reduced activity (15% compared to normal) for phosphoglycerate kinase (PGK1), a glycolytic enzyme encoded by PGK1. A diagnosis of PGK1 deficiency was established by molecular analysis which detected an approximately 886kb deletion involving the polyadenylation site in the 3'UTR of the PGK1 gene. RNA analysis showed significantly reduced PGK1 transcript levels (30% compared to normal). This is the first deletion reported in the PGK1 gene and is the first pathogenic variant involving the 3'UTR polyadenylation site of this gene. Our report emphasizes the role of 3'UTR variants in human disorders and underscores the need for exploring noncoding regions of disease-associated genes when seeking a molecular diagnosis.

A novel point mutation affecting Asn76 of dystrophin protein leads to dystrophinopathy

Mutations in the DMD gene lead to Duchenne and Becker muscular dystrophy (DMD/BMD). Missense mutations are rare cause of DMD/BMD. A six-month-old male patient presented with mild generalized muscle weakness, hypotonia, and delayed motor development. Dystrophinopathy was suspected because of highly elevated serum creatine kinase level (1497 U/L) and tiered DMD gene analysis was performed. Multiplex ligation-dependent probe amplification (MLPA) assay showed deletion of exon 4, which could not be confirmed by another method. Sequencing of exon 4 revealed a novel de novo point mutation (c.227A>T, p.Asn76Ile) in the N-terminal actin-binding domain (N-ABD) of dystrophin protein. The false positive MLPA result was explained by the fact that the affected nucleotide lies directly at the 3' ligation site of the MLPA probe. Sequencing of the whole coding region of DMD gene proved c.227A>T to be the sole variant being potentially pathogenic. According to in silico analyses the mutation was predicted to be highly destabilizing on N-ABD structure possibly leading to protein malfunction. Muscle biopsy was performed and dystrophin immunohistochemistry results were suggestive of BMD. Our results highlight the importance of confirmatory testing of single-exon deletions detected by MLPA and we describe a novel, destabilizing missense mutation in the DMD gene.

Mutations in ARMC9, which Encodes a Basal Body Protein, Cause Joubert Syndrome in Humans and Ciliopathy Phenotypes in Zebrafish

Joubert syndrome (JS) is a recessive neurodevelopmental disorder characterized by hypotonia, ataxia, abnormal eye movements, and variable cognitive impairment. It is defined by a distinctive brain malformation known as the "molar tooth sign" on axial MRI. Subsets of affected individuals have malformations such as coloboma, polydactyly, and encephalocele, as well as progressive retinal dystrophy, fibrocystic kidney disease, and liver fibrosis. More than 35 genes have been associated with JS, but in a subset of families the genetic cause remains unknown. All of the gene products localize in and around the primary cilium, making JS a canonical ciliopathy. Ciliopathies are unified by their overlapping clinical features and underlying mechanisms involving ciliary dysfunction. In this work, we identify biallelic rare, predicted-deleterious ARMC9 variants (stop-gain, missense, splice-site, and single-exon deletion) in 11 individuals with JS from 8 families, accounting for approximately 1% of the disorder. The associated phenotypes range from isolated neurological involvement to JS with retinal dystrophy, additional brain abnormalities (e.g., heterotopia, Dandy-Walker malformation), pituitary insufficiency, and/or synpolydactyly. We show that ARMC9 localizes to the basal body of the cilium and is upregulated during ciliogenesis. Typical ciliopathy phenotypes (curved body shape, retinal dystrophy, coloboma, and decreased cilia) in a CRISPR/Cas9-engineered zebrafish mutant model provide additional support for ARMC9 as a ciliopathy-associated gene. Identifying ARMC9 mutations as a cause of JS takes us one step closer to a full genetic understanding of this important disorder and enables future functional work to define the central biological mechanisms underlying JS and other ciliopathies.

Validation of copy number variation analysis for next-generation sequencing diagnostics.

Although a common cause of disease, copy number variants (CNVs) have not routinely been identified from next-generation sequencing (NGS) data in a clinical context. This study aimed to examine the sensitivity and specificity of a widely used software package, ExomeDepth, to identify CNVs from targeted NGS data sets. We benchmarked the accuracy of CNV detection using ExomeDepth v1.1.6 applied to targeted NGS data sets by comparison to CNV events detected through whole-genome sequencing for 25 individuals and determined the sensitivity and specificity of ExomeDepth applied to these targeted NGS data sets to be 100% and 99.8%, respectively. To define quality assurance metrics for CNV surveillance through ExomeDepth, we undertook simulation of single-exon (n=1000) and multiple-exon heterozygous deletion events (n=1749), determining a sensitivity of 97% (n=2749). We identified that the extent of sequencing coverage, the inter- and intra-sample variability in the depth of sequencing coverage and the composition of analysis regions are all important determinants of successful CNV surveillance through ExomeDepth. We then applied these quality assurance metrics during CNV surveillance for 140 individuals across 12 distinct clinical areas, encompassing over 500 potential rare disease diagnoses. All 140 individuals lacked molecular diagnoses after routine clinical NGS testing, and by application of ExomeDepth, we identified 17 CNVs contributing to the cause of a Mendelian disorder. Our findings support the integration of CNV detection using ExomeDepth v1.1.6 with routine targeted NGS diagnostic services for Mendelian disorders. Implementation of this strategy increases diagnostic yields and enhances clinical care.

Multiplex ligation-dependent probe amplification as first mutation screening for large deletions and duplications in haemophilia.

Molecular characterization has shown a wide mutational spectrum underlying haemophilia A (HA) and haemophilia B (HB). Different molecular assays have allowed laboratories to perform genetic testing for F8 and F9 mutations. Recently, multiplex ligation-dependent probe amplification (MLPA), a simple technique for relative quantitation of targeted genomic regions, has been introduced in HA and HB for detection of large deletions and duplications. We want to verify if MLPA might be used at the beginning of the molecular investigation. We used it to test 22 patients with suspected large deletions, nine patients negative for mutation detection by other methods and finally, 45 new patients as their first screening test. Carrier status was also established in 28 related females and gross rearrangements were also searched for by MLPA in 19 females with reduced FVIII or FIX levels. All suspected deletions were confirmed apart from two patients. In patients with a negative screening test, MLPA revealed one large duplication, while in two patients where MLPA was used as the first screening step, an exon duplication was detected. In females with reduced FVIII or FIX, no large deletions or duplications were found. Owing to its simplicity, MLPA seems useful at the beginning of the molecular investigation, saving all the following steps, where positive. Single exon deletion diagnosis requires caution due to the risk of misdiagnosis, but benefits of MLPA appear to overcome the pitfalls.

Duchenne Muscular Dystrophy and Becker Muscular Dystrophy Confirmed by Multiplex Ligation-Dependent Probe Amplification: Genotype-Phenotype Correlation in a Large Cohort

Background and PurposeStudies of cases of Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) confirmed by multiplex ligation-dependent probe amplification (MLPA) have determined the clinical characteristics, genotype, and relations between the reading frame and phenotype for different countries. This is the first such study from India.MethodsA retrospective genotype-phenotype analysis of 317 MLPA-confirmed patients with DMD or BMD who visited the neuromuscular clinic of a quaternary referral center in southern India.ResultsThe 317 patients comprised 279 cases of DMD (88%), 32 of BMD (10.1%), and 6 of intermediate phenotype (1.9%). Deletions accounted for 91.8% of cases, with duplications causing the remaining 8.2%. There were 254 cases of DMD (91%) with deletions and 25 (9%) due to duplications, and 31 cases (96.8%) of BMD with deletions and 1 (3.2%) due to duplication. All six cases of intermediate type were due to deletions. The most-common mutation was a single-exon deletion. Deletions of six or fewer exons constituted 68.8% of cases. The deletion of exon 50 was the most common. The reading-frame rule held in 90% of DMD and 94% of BMD cases. A tendency toward a lower IQ and earlier wheelchair dependence was observed with distal exon deletions, though a significant correlation was not found.ConclusionsThe reading-frame rule held in 90% to 94% of children, which is consistent with reports from other parts of the world. However, testing by MLPA is a limitation, and advanced sequencing methods including analysis of the structure of mutant dystrophin is needed for more-accurate assessments of the genotype-phenotype correlation.

Copy number variation as a genetic basis for heterotaxy and heterotaxy-spectrum congenital heart defects.

Genomic disorders and rare copy number abnormalities are identified in 15-25% of patients with syndromic conditions, but their prevalence in individuals with isolated birth defects is less clear. A spectrum of congenital heart defects (CHDs) is seen in heterotaxy, a highly heritable and genetically heterogeneous multiple congenital anomaly syndrome resulting from failure to properly establish left-right (L-R) organ asymmetry during early embryonic development. To identify novel genetic causes of heterotaxy, we analysed copy number variants (CNVs) in 225 patients with heterotaxy and heterotaxy-spectrum CHDs using array-based genotyping methods. Clinically relevant CNVs were identified in approximately 20% of patients and encompassed both known and putative heterotaxy genes. Patients were carefully phenotyped, revealing a significant association of abdominal situs inversus with pathogenic or likely pathogenic CNVs, while d-transposition of the great arteries was more frequently associated with common CNVs. Identified cytogenetic abnormalities ranged from large unbalanced translocations to smaller, kilobase-scale CNVs, including a rare, single exon deletion in ZIC3, a gene known to cause X-linked heterotaxy. Morpholino loss-of-function experiments in Xenopus support a role for one of these novel candidates, the platelet isoform of phosphofructokinase-1 (PFKP) in heterotaxy. Collectively, our results confirm a high CNV yield for array-based testing in patients with heterotaxy, and support use of CNV analysis for identification of novel biological processes relevant to human laterality.This article is part of the themed issue 'Provocative questions in left-right asymmetry'.

Homozygous and hemizygous CNV detection from exome sequencing data in a Mendelian disease cohort.

We developed an algorithm, HMZDelFinder, that uses whole exome sequencing (WES) data to identify rare and intragenic homozygous and hemizygous (HMZ) deletions that may represent complete loss-of-function of the indicated gene. HMZDelFinder was applied to 4866 samples in the Baylor–Hopkins Center for Mendelian Genomics (BHCMG) cohort and detected 773 HMZ deletion calls (567 homozygous or 206 hemizygous) with an estimated sensitivity of 86.5% (82% for single-exonic and 88% for multi-exonic calls) and precision of 78% (53% single-exonic and 96% for multi-exonic calls). Out of 773 HMZDelFinder-detected deletion calls, 82 were subjected to array comparative genomic hybridization (aCGH) and/or breakpoint PCR and 64 were confirmed. These include 18 single-exon deletions out of which 8 were exclusively detected by HMZDelFinder and not by any of seven other CNV detection tools examined. Further investigation of the 64 validated deletion calls revealed at least 15 pathogenic HMZ deletions. Of those, 7 accounted for 17–50% of pathogenic CNVs in different disease cohorts where 7.1–11% of the molecular diagnosis solved rate was attributed to CNVs. In summary, we present an algorithm to detect rare, intragenic, single-exon deletion CNVs using WES data; this tool can be useful for disease gene discovery efforts and clinical WES analyses.

Mutation analysis of 81 cases with Duchenne/Becker muscular dystrophy

To perform mutation analysis for 81 unrelated patients with Duchenne/Becker muscular dystrophy (DMD/BMD) from Henan Province. Multiplex ligation-dependent probe amplification (MLPA) was used to detect potential deletion/duplications of the DMD gene. Those with single exon deletions were validated with PCR amplification and Sanger sequencing to rule out false positive results. Patients with negative MLPA results were further analyzed with next-generation sequencing (NGS), and the result was validated by Sanger sequencing. DMD gene deletion/duplications were detected in 67 cases by MLPA, and exons 45-54 was the most frequently deleted. The phenotypes of 79.1% patients with a deletion or duplication has conformed to the reading frame rule. In addition, 13 mutations were detected by NGS and Sanger sequencing, which included 6 novel mutations including one frameshift mutation c.4708-4709insTG and 5 nonsense mutations (c.8812G>T, c.2131A>T, c.6035T>A, c.3426C>A, and c.3055C>T). This results have enriched the DMD gene mutation database. Combined MLPA, NGS and Sanger sequencing can greatly enhance the sensibility and specificity of genetic testing for the DMD/BMD.

A Novel Multiplex NGS-Based Digital MLPA Assay for Copy Number Detection of 700 Target Sequences in Childhood Acute Lymphoblastic Leukemia

▪Background: Recurrent and clonal genetic alterations are characteristic of different subtypes of pediatric acute lymphoblastic leukemia (ALL) and several of them are strong independent predictors of patient outcome. Multiplex Ligation-dependent Probe Amplification (MLPA) has become one of the standard methods for detection of common copy number alterations (CNAs), including IKZF1 deletions, which are associated with a poor outcome. However, standard MLPA assays only accommodate a maximum of 60 MLPA probes. In order to increase the number of target sequences in one assay, a next generation sequencing (NGS)-based MLPA variant has been developed. This digitalMLPA assay is based on the well-known MLPA procedure but can include up to 1000 probes in a single reaction, uses minute amounts of DNA (≥20ng) and can be analysed on all Illumina NGS platforms.Methods: A digitalMLPA assay was designed and optimised to detect CNAs of 55 key target genes and regions in childhood ALL, including deletions of B-cell differentiation and cell cycle control genes (PAX5, IKZF1/2/3, EBF1, RB1, CDKN2A/B, ETV6, and BTG1), iAMP21 and rearrangements of the PAR1 region, T-cell ALL associated aberrations (STIL-TAL1, LEF1, CASP8AP2, MYB, EZH2, MLLT3, NUP214-ABL1, PTEN, LMO1/2, NF1, SUZ12, PTPN2, PHF6), ERG and TP53 deletions. Several genetic alterations of potential prognostic and/or therapeutic relevance in ALL have also been included (NOTCH1, CD200/BTLA, VPREB1, TBL1XR1, PDGFRB-EBF1, IGHM, NR3C1/2, CREBBP, CTCF, ADD3, EPHA1, FHIT, SPRED1 and TOX). All target genes are covered by at least 3 digitalMLPA probes (~450 probes in total). Moreover, a set of 200 probes was designed for genome-wide detection of gross ploidy changes (high hyper- or hypodiploidy) and to determine the extent of CNAs, while also acting as reference probes for data normalization. Performance of all probes has been extensively tested on genomic DNA from healthy individuals and positive cell lines. Only probes with a standard deviation <0.12 were included. All probes were also tested under various experimental conditions, such as different salt, probe and polymerase concentrations. A series of 76 pediatric ALL patient samples (including both B-ALL and T-ALL samples), previously characterized for specific genetic aberrations by array CGH (aCGH) and/or SNP array, has been analysed single-blinded using the digitalMLPA assay. Results were compared to those obtained from standard MLPA assays (P335 ALL-IKZF1 and P327 iAMP21-ERG), which contain probes with different ligation sites for the respective genes. A dilution series of three B-ALL patient samples was analysed to determine the detection limit for subclonal aberrations.Results: All aberrations previously identified by other methods in 67 pediatric ALL samples, were also identified using the digitalMLPA assay. These included whole chromosome gains and losses, whole gene deletions or gains, iAMP21, fusion genes (STIL-TAL1, NUP214-ABL1 and PDGFRB-EBF1) and intragenic gene deletions (IKZF1, ERG, CDKN2A/B, ETV6, PAX5 RUNX1, RB1, LEF1, NR3C1, RAG2, VPREB1, MLLT3, BTG1 and PTEN). Of interest was a case of high hyperdiploidy, which was correctly identified by digitalMLPA, while by aCGH analysis this case was misinterpreted as having multiple deletions. Among several other intragenic deletions, a heterozygous deletion of ERG exons 5-9 was observed in one patient. In addition, several cases of homozygous single-exon deletions were observed (e.g. IKZF1 exon 8, LEF1exon 3) and confirmed by aCGH. These findings should be further investigated with respect to their clinical impact. Results from the dilution series indicated that subclonal aberrations can be reliably detected by this digitalMLPA assay if present in at least 20- 30% of tumour cells.Conclusions: This study demonstrates that digitalMLPA is a reliable technique that can be used to genetically characterize clinical samples of ALL patients. Experiments can be performed on small amounts of DNA in a high-throughput and cost-effective fashion. Because of the targeted approach, data analysis will be much easier as compared to array or other sequencing platforms. These results merit further consideration of (digital)MLPA as a valuable alternative for genetic work-up of newly diagnosed ALL patients. DisclosuresNo relevant conflicts of interest to declare.

De novo and inherited mutations in the X-linked gene CLCN4 are associated with syndromic intellectual disability and behavior and seizure disorders in males and females

Variants in CLCN4, which encodes the chloride/hydrogen ion exchanger CIC-4 prominently expressed in brain, were recently described to cause X-linked intellectual disability and epilepsy. We present detailed phenotypic information on 52 individuals from 16 families with CLCN4-related disorder: 5 affected females and 2 affected males with a de novo variant in CLCN4 (6 individuals previously unreported) and 27 affected males, 3 affected females and 15 asymptomatic female carriers from 9 families with inherited CLCN4 variants (4 families previously unreported). Intellectual disability ranged from borderline to profound. Behavioral and psychiatric disorders were common in both child- and adulthood, and included autistic features, mood disorders, obsessive–compulsive behaviors and hetero- and autoaggression. Epilepsy was common, with severity ranging from epileptic encephalopathy to well-controlled seizures. Several affected individuals showed white matter changes on cerebral neuroimaging and progressive neurological symptoms, including movement disorders and spasticity. Heterozygous females can be as severely affected as males. The variability of symptoms in females is not correlated with the X inactivation pattern studied in their blood. The mutation spectrum includes frameshift, missense and splice site variants and one single-exon deletion. All missense variants were predicted to affect CLCN4’s function based on in silico tools and either segregated with the phenotype in the family or were de novo. Pathogenicity of all previously unreported missense variants was further supported by electrophysiological studies in Xenopus laevis oocytes. We compare CLCN4-related disorder with conditions related to dysfunction of other members of the CLC family.

Mutation screening of 433 families with Duchenne/Becker muscular dystrophy

Mutation analysis of unrelated families with Duchenne/Becker muscular dystrophy (DMD/BMD) was performed to investigate the characteristic of DMD gene mutation, especially the distribution pattern of point mutation of DMD gene in Chinese population. A total of 433 unrelated DMD/BMD families were collected at the Center of Prenatal Diagnosis of the First Affiliated Hospital of Zhengzhou University from March 2010 to December 2014. The deletions or duplications in 79 exons of DMD gene were screened using multiplex ligation-dependent probe amplification (MLPA). Any single-exon deletion detected by MLPA was further validated by PCR amplification. In the 117 unrelated Chinese families in which large-scale deletions and duplications had been excluded by MLPA, the point mutation in 79 exons of DMD gene were tested in the propositus using next-generation sequencing (NGS), and further verified the point mutation using Sanger sequencing. In the 433 unrelated DMD/BMD families, 316 families with DMD deletions/duplications were identified by MLPA. Out of 57 single-exon deletions detected by MLPA, 3 were found as point mutations by PCR and Sanger sequencing, including 2 nonsense mutation (c.1729G>T [p.Glu577X], c. 3346A>T [p.Lys1116X]) and 1 frame-shift mutation (c.8605_8606delGT [p.Val2869ThrfsX25]). Direct sequencing with Ion PGM and Sanger sequencing in 117 families with negative results in MLPA detected 92 different point mutations in 96 families, including 46 novel mutations, 42 previously reported ones, and 4 possible polymorphisms (rs189143447, rs202008454, rs200213555, rs187617705). The 46 novel mutations consisted of 16 nonsense mutations (c.100A>T [p.Lys34X], c. 1201C>T [p.Gln401X], c. 1707C>A [p.Cys569X], c. 1831G>T [p.Glu611X], c. 1912C>T [p.Gln638X], c. 2213C>G [p.Ser738X], c. 3673_3673delA [p.Ile1225X], c. 3774C>A [p.Cys1258X], c. 4858G>T [p.Glu1620X], c. 5764A>T [p.Lys1922X], c. 6035T>G [p.Leu2012X], c. 6408G>A [p.Trp2136X], c. 7717C>T [p.Gln2573X], c. 7864G>T [p.Glu2622X], c. 8184_8185insT [p.Lys2729X], c. 8215C>T [p.Gln2739X]), 5 missense mutations (c.139G>A [p.Gly47Arg], c. 238G>C [p.Ala80Pro], c. 335G>T [p.Trp112Leu], c. 804A>C [p.Leu268Phe], c. 1149G>T [p.Glu383Asp]), 6 splice-site mutations (c.2293-3C>A, c. 2380+ 1G>T, c. 3277-1G>C, c.4519-7A>G, c. 5740-15G>T, c. 7661-1G>C), 16 small deletions (c.688_688delA [p.Met230CysfsX14], c.1760_1791del32 [p.Thr587IlefsX37], c. 2271_2271delA [p.Asp774ThrfsX22], c. 2281_2285delGAAAA [p.Glu761SerfsX10], c. 2527_2527delG [p.Glu843SerfsX3], c. 3405_3405delC [p.Asn1135LysfsX18], c. 4450_4450delC [p.His1484ThrfsX14], c. 4770_4770delA [p.Thr1590ThrfsX5], c. 4937_4937delA [p.Glu1646GlyfsX11], c. 5253_5256delATTA [p.Lys1751LysfsX2], c. 5654_5654delA [p.Gln1885ArgfsX6], c. 7441_7441delG [p.Glu2481AsnfsX13], c. 7860_7860delC [p.Ile2620IlefsX18], c. 8668-8668delG /c.8668+ 1-8668+ 1delG, c. 9009_9009delC [p.Thr3003ThrfsX18], c. 9021_9021delT [p.Ile3007IlefsX14]), and 3 small insertions (c.305_306insG [p.Gly102GlyfsX4], c. 3116_3117insA [p.His1039GlufsX11], c. 9197_9198insATCTC [p.Ser3066SerfsX25]). And 87.4% (83/95) of the pathologic point mutations disrupted the translational reading frame (46 nonsense mutations, 24 frame-shift mutations, and 13 splice-site mutations). Inexpensive and efficient genetic/prenatal diagnosis of DMD/BMD may be plausible by MLPA analysis, NGS, and Sanger sequencing. Most of the mutations identified in this study led to a predictable premature stop codon or splicing defects, resulting in defective function of dystrophin.

Identification of genomic deletions causing inherited retinal degenerations by coverage analysis of whole exome sequencing data

BackgroundInherited retinal degenerations (IRDs) are a common cause of visual disturbance with a high clinical and genetic heterogeneity. Recent sequencing techniques such as whole exome sequencing (WES) contribute to the...

FANCA Gene Mutations with 8 Novel Molecular Changes in Indian Fanconi Anemia Patients.

Fanconi anemia (FA), a rare heterogeneous genetic disorder, is known to be associated with 19 genes and a spectrum of clinical features. We studied FANCA molecular changes in 34 unrelated and 2 siblings of Indian patients with FA and have identified 26 different molecular changes of FANCA gene, of which 8 were novel mutations (a small deletion c.2500delC, 4 non-sense mutations c.2182C>T, c.2630C>G, c.3677C>G, c.3189G>A; and 3 missense mutations; c.1273G>C, c.3679 G>C, and c.3992 T>C). Among these only 16 patients could be assigned FA-A complementation group, because we could not confirm single exon deletions detected by MLPA or cDNA amplification by secondary confirmation method and due to presence of heterozygous non-pathogenic variations or heterozygous pathogenic mutations. An effective molecular screening strategy should be developed for confirmation of these mutations and determining the breakpoints for single exon deletions.

Pitfalls of Multiple Ligation-Dependent Probe Amplifications in Detecting DMD Exon Deletions or Duplications

Multiple ligation-dependent probe amplifications (MLPAs) are a key technology for the molecular diagnosis of Duchenne/Becker muscular dystrophy, which is mainly caused by large gene arrangements. However, little is known about the false-positive rates of MLPA for this disease. Here, we review MLPA analysis results from 398 patients suspected to have Duchenne/Becker muscular dystrophy. MLPA assay was used for screening the entire coding region. If these amplifications produced normal results, direct sequencing was performed to search for sequence variations and to determine single-exon deletions, duplications, or indeterminate results. Using MLPA, 290 cases (72.9%) showed exon deletion or duplication results. Among those, 75 cases (25.9%) resulted in a deletion or duplication of a single exon. Direct sequencing revealed that 11 single-exon deletion cases resulted in false-positives due to sequence variations within the patient population interfering with probe binding at the probe-hybridization sites. Abnormal MLPA results were closely related to the type of sequence change and the position within the probe-hybridization locus. The most common type was C-T transition (n = 19, 55.9%). Abnormal MLPA results correlated with CA mismatch and low melting temperature (≤75°C). False-positive events for large gene rearrangements involving a single exon in DMD accounted for approximately 15% (11/75). Therefore, careful design of MLPA probes is required to avoid false-positive results.

Analysis of dystrophin gene in Iranian Duchenne and Becker muscular dystrophies patients and identification of a novel mutation.

Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) are the most frequent muscular dystrophies. Present study aimed to determine the frequency of dystrophin gene alterations in Iranian DMD/BMD patients using molecular techniques. 146 Iranian DMD/BMD patients have been analyzed using two devised sets of multiplex polymerase chain reaction (M-PCR) followed by multiple ligation-dependent probe amplification (MLPA). Two isolated DMD and BMD patients were analyzed by DNA sequencing. 30.9% of patients had single-exon deletion while group and contiguous exon deletions were identified in 41% of the patients. The most numerous exon deletions included exons 45-50 and were identified in the first M-PCR set. Deletion detection rate was 99% in first M-PCR set and remaining deletions (1%) were identified in the second M-PCR set. MLPA analysis showed that there were two exons 3-5 and 41-43 duplications (1.4%) in a BMD and a DMD patient, respectively. Two nonsense mutations including c.633dupA and c.6283 C>T were, respectively, found in a DMD and BMD patient in which c.633dupA has not ever been reported in DMD mutation database and was pathogenic mutation. Besides the report of frequency of dystrophin gene alteration in a subset of Iranian DMD/BMD patients, it was revealed that the proposed M-PCR protocol can be useful in the initial step of molecular diagnosis of DMD/BMD. Exon sequencing would be the final step in determining the mutation status of DMD/BMD patients following MLPA.

AB032. Mutation spectrum in the dystrophin gene disclosed by multiplex ligation-dependent probe amplification in 181 Vietnamese Duchenne/Becker muscular dystrophy patients.

Duchenne/Becker muscular dystrophy (DMD/BMD) the most common X-linked muscular dystrophy is caused by mutation in dystrophin gene. Deletion and duplication in the dystrophin gene account for 60-70% of mutation. Multiplex ligation-dependent probe amplification (MLPA) is the most powerful and convenient method to identify exon deletions or duplications in the dystrophin gene because of its overall gene coverage. The present investigation was designed to detect mutation in the dystrophin gene in 181 unrelated Vietnamese Becker/Duchenne patients using MLPA analysis. Among the 181 cases, deletions and duplications encompassing one or more exons were identified in 105 (58%) or 12 (6.6%) cases, respectively. Deletions were found to cluster in the proximal (14.3%) and central hotspot regions (72.4%); 14% were observed to have gross deletions and 1.2% had deletion out of hotspot regions (exon 61-67). The deletion patterns were categorized into 48 patterns. Deletion of exon 48-50 or 45-50 where the most common pattern was deletion of exon 48-50, which was found in 11 cases (10%). Single-exon deletion was found in 14 cases (13%) by MLPA. Further examination disclosed that one of them was not an exon deletion but a single-nucleotide change (c.2227C > T) leading to a nonsense mutation. Outliers from the reading frame rule were 11 DMD (10.4%). Remarkably, 25 and 14 cases were found treatable by exon 51 and 53 skipping, respectively. From these findings, the largest mutation database of Vietnam dystrophinopathy was established.