BACKGROUND: Primary deficiencies in mannosylation of N-glycans are seen in a majority of patients with congenital disorders of glycosylation (CDG). We report the discovery of a series of novel N-glycans in sera, plasma, and cultured skin fibroblasts from patients with CDG having deficient mannosylation. METHOD: We used LC-MS/MS and MALDI-TOF-MS analysis to identify and quantify a novel N-linked tetrasaccharide linked to the protein core, an N-tetrasaccharide (Neu5Acα2,6Galβ1,4-GlcNAcβ1,4GlcNAc) in plasma, serum glycoproteins, and a fibroblast lysate from patients with CDG caused by ALG1 [ALG1 (asparagine-linked glycosylation protein 1), chitobiosyldiphosphodolichol β-mannosyltransferase], PMM2 (phosphomannomutase 2), and MPI (mannose phosphate isomerase). RESULTS: Glycoproteins in sera, plasma, or cell lysate from ALG1-CDG, PMM2-CDG, and MPI-CDG patients had substantially more N-tetrasaccharide than unaffected controls. We observed a >80% decline in relative concentrations of the N-tetrasaccharide in MPICDG plasma after mannose therapy in 1 patient and in ALG1-CDG fibroblasts in vitro supplemented with mannose. CONCLUSIONS: This novel N-tetrasaccharide could serve as a diagnostic marker of ALG1-, PMM2-, or MPI-CDG for screening of these 3 common CDG subtypes that comprise >70% of CDG type I patients. Its quantification by LC-MS/MS may be useful for monitoring therapeutic efficacy of mannose. The discovery of these small N-glycans also indicates the presence of an alternative pathway in N-glycosylation not recognized previously, but its biological significance remains to be studied.

Objectives To determine the incidence of pathogenic SCN8A variants in a cohort of epilepsy patients referred for clinical genetic testing. We also investigated the contribution of SCN8A to autism spectrum disorder, intellectual disability, and neuromuscular disorders in individuals referred for clinical genetic testing at the same testing laboratory. Methods Sequence data from 275 epilepsy panels screened by Emory Genetics Laboratory were reviewed for variants in SCN8A. Two additional cases with variants in SCN8A were ascertained from other testing laboratories. Parental samples were tested for variant segregation and clinical histories were examined. SCN8A variants detected from gene panel analyses for autism spectrum disorder, intellectual disability, and neuromuscular disorders were also examined. Results Five variants in SCN8A were identified in five individuals with epilepsy. Three variants were de novo, one was inherited from an affected parent, and one was inherited from an unaffected parent. Four of the individuals have epilepsy and developmental delay/intellectual disability. The remaining individual has a milder epilepsy presentation without cognitive impairment. We also identified an amino acid substitution at an evolutionarily conserved SCN8A residue in a patient who was screened on the autism spectrum disorder panel. Additionally, we examined the distribution of pathogenic SCN8A variants across the Na v 1.6 channel and identified four distinct clusters of variants. These clusters are primarily located in regions of the channel that are important for the kinetics of channel inactivation. Conclusions Variants in SCN8A may be responsible for a spectrum of epilepsies as well as other neurodevelopmental disorders without seizures. The predominant pathogenic mechanism appears to involve disruption of channel inactivation, leading to gain-of-function effects.

Revolutionary changes in sequencing technology and the desire to develop therapeutics for rare diseases have led to the generation of an enormous amount of genomic data in the last 5 years. Large-scale sequencing done in both research and diagnostic laboratories has linked many new genes to rare diseases, but has also generated a number of variants that we cannot interpret today. It is clear that we remain a long way from a complete understanding of the genomic variation in the human genome and its association with human health and disease. Recent studies identified susceptibility markers to infectious diseases and also the contribution of rare variants to complex diseases in different populations. The sequencing revolution has also led to the creation of a large number of databases that act as "keepers" of data, and in many cases give an interpretation of the effect of the variant. This interpretation is based on reports in the literature, prediction models, and in some cases is accompanied by functional evidence. As we move toward the practice of genomic medicine, and consider its place in "personalized medicine," it is time to ask ourselves how we can aggregate this wealth of data into a single database for multiple users with different goals.

Clinical genetics laboratories have recently adopted guidelines for the interpretation of sequence variants set by the American College of Medical Genetics (ACMG) and Association for Molecular Pathology (AMP). The use of in silico algorithms to predict whether amino acid substitutions result in human disease is inconsistent across clinical laboratories. The clinical genetics community must carefully consider how in silico predictions can be incorporated into variant interpretation in clinical practice.Please see related Research article: https://doi.org/10.1186/s13059-017-1353-5.

Objective: Dysferlin is a large transmembrane protein that functions in critical processes of membrane repair and vesicle fusion. Dysferlin-deficiency due to mutations in the dysferlin gene leads to muscular dystrophy (Miyoshi myopathy (MM), limb girdle muscular dystrophy type 2B (LGMD2B), distal myopathy with anterior tibial onset (DMAT)), typically with early adult onset. At least 416 pathogenic dysferlin mutations are known, but for approximately 17% of patients, one or both of their pathogenic variants remain undefined following standard exon sequencing methods that interrogate exons and nearby flanking intronic regions but not the majority of intronic regions. Methods: We sequenced RNA from myogenic cells to identify a novel dysferlin pathogenic variant in two affected siblings that previously had only one disease-causing variant identified. We designed antisense oligonucleotides (AONs) to bypass the effects of this mutation on RNA splicing. Results: We identified a new pathogenic point mutation deep within dysferlin intron 50i. This intronic variant causes aberrant mRNA splicing and inclusion of an additional pseudoexon (PE, we term PE50.1) within the mature dysferlin mRNA. PE50.1 inclusion alters the protein sequence, causing premature translation termination. We identified this mutation in 23 dysferlinopathy patients (seventeen families), revealing it to be one of the more prevalent dysferlin mutations. We used AON-mediated exon skipping to correct the aberrant PE50.1 splicing events in vitro, which increased normal mRNA production and significantly restored dysferlin protein expression. Interpretation: Deep intronic mutations can be a common underlying cause of dysferlinopathy, and importantly, could be treatable with AON-based exon-skipping strategies.

Purpose: The aim of this study was to explore specific conditions and types of genetic variants that specialists in genetics recommend should be returned as incidental findings in clinical sequencing. Methods: Sixteen specialists in clinical genetics and/or molecular medicine selected variants in 99 common conditions to return to the ordering physician if discovered incidentally through whole-genome sequencing. For most conditions, the specialists independently considered three molecular scenarios for both adults and minor children: a known pathogenic mutation, a truncating variant presumed pathogenic (where other truncating variants are known to be pathogenic), and a missense variant predicted in silico to be pathogenic. Results: On average, for adults and children, respectively, each specialist selected 83.5 and 79.0 conditions or genes of 99 in the known pathogenic mutation categories, 57.0 and 53.5 of 72 in the truncating variant categories, and 33.4 and 29.7 of 72 in the missense variant categories. Concordance in favor of disclosure within the adult/known pathogenic mutation category was 100% for 21 conditions or genes and 80% or higher for 64 conditions or genes. Conclusion: Specialists were highly concordant for the return of findings for 64 conditions or genes if discovered incidentally during whole-exome sequencing or whole-genome sequencing.

The increasing use of advanced nucleic acid sequencing technologies for clinical diagnostics and therapeutics has made vital understanding the costs of performing these procedures and their value to patients, providers, and payers. The Association for Molecular Pathology invested in a cost and value analysis of specific genomic sequencing procedures (GSPs) newly coded by the American Medical Association Current Procedural Terminology Editorial Panel. Cost data and work effort, including the development and use of data analysis pipelines, were gathered from representative laboratories currently performing these GSPs. Results were aggregated to generate representative cost ranges given the complexity and variability of performing the tests. Cost-impact models for three clinical scenarios were generated with assistance from key opinion leaders: impact of using a targeted gene panel in optimizing care for patients with advanced non-small-cell lung cancer, use of a targeted gene panel in the diagnosis and management of patients with sensorineural hearing loss, and exome sequencing in the diagnosis and management of children with neurodevelopmental disorders of unknown genetic etiology. Each model demonstrated value by either reducing health care costs or identifying appropriate care pathways. The templates generated will aid laboratories in assessing their individual costs, considering the value structure in their own patient populations, and contributing their data to the ongoing dialogue regarding the impact of GSPs on improving patient care.

PURPOSE: While the diagnostic success of genomic sequencing expands, the complexity of this testing should not be overlooked. Numerous laboratory processes are required to support the identification, interpretation, and reporting of clinically significant variants. This study aimed to examine the workflow and reporting procedures among US laboratories to highlight shared practices and identify areas in need of standardization. METHODS: Surveys and follow-up interviews were conducted with laboratories offering exome and/or genome sequencing to support a research program or for routine clinical services. The 73-item survey elicited multiple choice and free-text responses that were later clarified with phone interviews. RESULTS: Twenty-one laboratories participated. Practices highly concordant across all groups included consent documentation, multiperson case review, and enabling patient opt-out of incidental or secondary findings analysis. Noted divergence included use of phenotypic data to inform case analysis and interpretation and reporting of case-specific quality metrics and methods. Few laboratory policies detailed procedures for data reanalysis, data sharing, or patient access to data. C ONCLUSION: This study provides an overview of practices and policies of experienced exome and genome sequencing laboratories. The results enable broader consideration of which practices are becoming standard approaches, where divergence remains, and areas of development in best practice guidelines that may be helpful.

Biliary atresia (BA) is the most common cause of end-stage liver disease in children and the primary indication for pediatric liver transplantation, yet underlying etiologies remain unknown. Approximately 10% of infants affected by BA exhibit various laterality defects (heterotaxy) including splenic abnormalities and complex cardiac malformations—a distinctive subgroup commonly referred to as the biliary atresia splenic malformation (BASM) syndrome. We hypothesized that genetic factors linking laterality features with the etiopathogenesis of BA in BASM patients could be identified through whole-exome sequencing (WES) of an affected cohort. DNA specimens from 67 BASM subjects, including 58 patient–parent trios, from the National Institute of Diabetes and Digestive and Kidney Diseases–supported Childhood Liver Disease Research Network (ChiLDReN) underwent WES. Candidate gene variants derived from a prespecified set of 2,016 genes associated with ciliary dysgenesis and/or dysfunction or cholestasis were prioritized according to pathogenicity, population frequency, and mode of inheritance. Five BASM subjects harbored rare and potentially deleterious biallelic variants in polycystic kidney disease 1 like 1 (PKD1L1), a gene associated with ciliary calcium signaling and embryonic laterality determination in fish, mice, and humans. Heterozygous PKD1L1 variants were found in 3 additional subjects. Immunohistochemical analysis of liver from the one BASM subject available revealed decreased PKD1L1 expression in bile duct epithelium when compared to normal livers and livers affected by other noncholestatic diseases. Conclusion: WES identified biallelic and heterozygous PKD1L1 variants of interest in 8 BASM subjects from the ChiLDReN data set; the dual roles for PKD1L1 in laterality determination and ciliary function suggest that PKD1L1 is a biologically plausible, cholangiocyte-expressed candidate gene for the BASM syndrome.