Over the last 5 years, RNA sequencing (RNA‐seq) has been established and is increasingly applied as an effective approach complementary to DNA sequencing in molecular diagnostics. Currently, three RNA phenotypes, aberrant expression, aberrant splicing, and allelic imbalance, are considered to provide information about pathogenic variants. By providing a high‐throughput, transcriptome‐wide functional readout on variants causing aberrant RNA phenotypes, RNA‐seq has increased diagnostic rates by about 15% over whole‐exome sequencing. This breakthrough encouraged the development of computational tools and pipelines aiming to streamline RNA‐seq analysis for implementation in clinical diagnostics. Although a number of studies showed the added value of RNA‐seq for the molecular diagnosis of individuals with Mendelian disorders, there is no formal consensus on assessing variant pathogenicity strength based on RNA phenotypes. Taking RNA‐seq as a functional assay for genetic variants, we evaluated the value of statistical significance and effect size of RNA phenotypes as evidence for the strength of variant pathogenicity. This was determined by the analysis of 394 pathogenic variants, of which 198 were associated with aberrant RNA phenotypes and 723 benign variants. Overall, this study seeks to establish recommendations for integrating functional RNA‐seq data into the the American College of Medical Genetics and Genomics and the Association for Molecular Pathology guidelines classification system.

Background: Recently, we have reported mutations in LARP7 gene, leading to neurodevelopmental disorders (NDDs), the most frequent cause of disability in children with a broad phenotype spectrum and diverse genetic landscape. Methods: Here, we present two Iranian patients from consanguineous families with syndromic intellectual disability, facial dysmorphism, and short stature. Results: Whole-exome sequencing (WES) revealed a novel homozygous stop-gain (c.C925T, p.R309X) variant and a previously known homozygous acceptor splice-site (c.1669-1_1671del) variant in LARP7 gene, indicating the diagnosis of Alazami syndrome. Conclusion: These identified variants in patients with Alazami syndrome were consistent with previously reported loss of function variants in LARP7 and provide further evidence that loss of function of LARP7 is the disease mechanism.

Although whole‐exome sequencing and whole‐genome sequencing has tremendously improved our understanding of the genetic etiology of human disorders, about half of the patients still do not receive a molecular diagnosis. The high fraction of variants with uncertain significance and the challenges of interpretation of noncoding variants have urged scientists to implement RNA sequencing (RNA‐seq) in the diagnostic approach as a high throughput assay to complement genomic data with functional evidence. RNA‐seq data can be used to identify aberrantly spliced genes, detect allele‐specific expression, and identify gene expression outliers. Amongst eight studies utilizing RNA‐seq, a mean diagnostic uplift of 15% has been reported. Here, we provide an overview of how RNA‐seq has been implemented to aid in identifying the causal variants of Mendelian disorders.