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Recommendations from the American College of Medical Genetics and Genomics and the Association for Molecular Pathology (ACMG/AMP) for interpreting sequence variants specify the use of computational predictors as "supporting" level of evidence for pathogenicity or benignity using criteria PP3 and BP4, respectively. However, score intervals defined by tool developers, and ACMG/AMP recommendations that require the consensus of multiple predictors, lack quantitative support. Previously, we described a probabilistic framework that quantified the strengths of evidence (supporting, moderate, strong, very strong) within ACMG/AMP recommendations. We have extended this framework to computational predictors and introduce a new standard that converts a tool's scores to PP3 and BP4 evidence strengths. Our approach is based on estimating the local positive predictive value and can calibrate any computational tool or other continuous-scale evidence on any variant type. We estimate thresholds (score intervals) corresponding to each strength of evidence for pathogenicity and benignity for thirteen missense variant interpretation tools, using carefully assembled independent data sets. Most tools achieved supporting evidence level for both pathogenic and benign classification using newly established thresholds. Multiple tools reached score thresholds justifying moderate and several reached strong evidence levels. One tool reached very strong evidence level for benign classification on some variants. Based on these findings, we provide recommendations for evidence-based revisions of the PP3 and BP4 ACMG/AMP criteria using individual tools and future assessment of computational methods for clinical interpretation.

Autosomal dominant (de novo) mutations in PBX1 are known to cause congenital abnormalities of the kidney and urinary tract (CAKUT), with or without extra-renal abnormalities. Using trio exome sequencing, we identified a PBX1 p.(Arg107Trp) mutation in a deceased one-day-old neonate presenting with CAKUT, asplenia, and severe bilateral diaphragmatic thinning and eventration. Further investigation by droplet digital PCR revealed that the mutation had occurred post-zygotically in the father, with different variant allele frequencies of the mosaic PBX1 mutation in blood (10%) and sperm (20%). Interestingly, the father had subclinical hydronephrosis in childhood. With an expected recurrence risk of one in five, chorionic villus sampling and prenatal diagnosis for the PBX1 mutation identified recurrence in a subsequent pregnancy. The family opted to continue the pregnancy and the second affected sibling was stillborn at 35 weeks, presenting with similar severe bilateral diaphragmatic eventration, microsplenia, and complete sex reversal (46, XY female). This study highlights the importance of follow-up studies for presumed de novo and low-level mosaic variants and broadens the phenotypic spectrum of developmental abnormalities caused by PBX1 mutations.

Rare disease investigators constantly face challenges in identifying additional cases to build evidence for gene‐disease causality. The Matchmaker Exchange (MME) addresses this limitation by providing a mechanism for matching patients across genomic centers via a federated network. The MME has revolutionized searching for additional cases by making it possible to query across institutional boundaries, so that what was once a laborious and manual process of contacting researchers is now automated and computable. However, while the MME network is beginning to scale, the growth of additional nodes is limited by the lack of easy‐to‐use solutions that can be implemented by any rare disease database owner, even one without significant software engineering resources. Here we describe matchbox, which is an open‐source, platform‐independent, portable bridge between any given rare disease genomic center and the MME network, which has already led to novel gene discoveries. We also describe how matchbox greatly reduces the barrier to participation by overcoming challenges for new databases to join the MME. Refereed/Peer-reviewed

Background Protein C (PC) (OMIM 612283) is an inactive zymogen of a serine protease (activated protein C, APC) which is an important regulator of blood coagulation factor Va and factor VIIIa, with deficiency associated with thromboembolic disease. Hereditary PC deficiency has been described as having both autosomal dominant and autosomal recessive inheritance (OMIM 612304 and 176860). Individuals heterozygous for PC deficiency may be asymptomatic, but those who are symptomatic most frequently present with deep vein thrombosis (DVT). Individuals homozygous (or compound heterozygous) for PC deficiency usually present with severe or fatal purpura fulminans early in life. Methods and Results We examined all nine exons, exon/intron boundaries and the promoter region of the protein C gene (PROC) using direct sequencing in two cases with PC deficiency with history of unprovoked DVT and pulmonary embolism. The first patient was a compound heterozygote for the c.541T>C and c.388_397del protein C gene mutations and the second patient was heterozygous for the c.541T>G protein C gene mutation. Conclusion A clear correlation between genotype and phenotype in PC deficiency has been difficult to establish and further studies are required for an improved understanding of genotype-pheno-type correlation in hereditary PC deficiency.