ClinVar Genomic variation as it relates to human health

This deletion of four nucleotides in SDHD is denoted c.337_340delGACT at the cDNA level and p.Asp113MetfsX21 (D113MfsX21) at the protein level. The normal sequence, with the bases that are deleted in brackets, is TACT[delGACT]ATGT. The deletion causes a frameshift, which changes an Aspartic Acid to a Methionine at codon 113, and creates a premature stop codon at position 21 of the new reading frame. This variant is predicted to cause loss of normal protein function through protein truncation as the last 47 amino acids are no longer translated. The disrupted region includes the helical transmembrane topological domain and the ubiquinone binding site (UniProt). This variant, also known as SDHD c.334_337delACTG, is a recurrent variant that has been reported in many individuals with early-onset and/or multiple paragangliomas/pheochromocytomas, and has been shown to track with disease in several families (Cascon 2002, Velasco 2005, Benn 2006, Lima 2007, Hermsen 2010, Lefebvre 2012). Paragangliomas from individuals carrying this variant have demonstrated loss of SDHB by IHC, and functional assays have shown that this variant results in a significant reduction of SDH enzyme activity and SDHB protein expression (Rapizzi 2012, Pai 2014). We consider this variant to be pathogenic. Of note, variants in the SDHD gene exhibit a parent-of-origin effect and, if shown to be pathogenic, typically cause symptoms only if inherited from the father.

For these reasons, this variant has been classified as Pathogenic. ClinVar contains an entry for this variant (Variation ID: 6912). This variant is also known as 13732delGACT. This premature translational stop signal has been observed in individuals with paragangliomas and/or pheochromocytomas (PMID: 12111639, 17848412, 21348866, 22517554, 27539324). It has also been observed to segregate with disease in related individuals. This variant is not present in population databases (gnomAD no frequency). This sequence change creates a premature translational stop signal (p.Asp113Metfs*21) in the SDHD gene. While this is not anticipated to result in nonsense mediated decay, it is expected to disrupt the last 47 amino acid(s) of the SDHD protein.

This variant is considered pathogenic. This variant creates a frameshift predicted to result in premature protein truncation.

The c.337_340delGACT pathogenic mutation, located in coding exon 4 of the SDHD gene, results from a deletion of 4 nucleotides at nucleotide positions 337 to 340, causing a translational frameshift with a predicted alternate stop codon (p.D113Mfs*21). This variant has been reported in many individuals with paragangliomas and/or pheochromocytomas (Cascon A et al. Eur J Hum Genet, 2002 Aug;10:457-61; Neumann HP et al. JAMA, 2004 Aug;292:943-51; Amar L et al. J Clin Oncol, 2005 Dec;23:8812-8; Velasco A et al. Diagn Mol Pathol, 2005 Jun;14:109-14; Benn DE et al. J Clin Endocrinol Metab, 2006 Mar;91:827-36; Castellano M et al. Ann N Y Acad Sci, 2006 Aug;1073:156-65; Lima J et al. J Clin Endocrinol Metab, 2007 Dec;92:4853-64; Sevilla MA et al. Otolaryngol Head Neck Surg, 2009 May;140:724-9; Hermsen MA et al. Cell Oncol, 2010 Jan;32:275-83; Hensen EF et al. Clin Genet, 2012 Mar;81:284-8; Lefebvre S et al. Horm Metab Res, 2012 May;44:334-8; Pai R et al. APMIS, 2014 Nov;122:1130-5; Pandit R et al. Eur J Endocrinol, 2016 Oct;175:311-23). This variant is also referred to as SDHD 13732delGACT and SDHD c.334_337delACTG in the literature. This alteration occurs at the 3' terminus of theSDHD gene, is not expected to trigger nonsense-mediated mRNA decay, and only impacts the last 29% of the protein. However, premature stop codons are typically deleterious in nature and the impacted region is critical for protein function (Ambry internal data). Based on the supporting evidence, this alteration is interpreted as a disease-causing mutation.