# Functional profiling of germline SDH variants associated with cancer susceptibility

> **NIH VA I01** · PORTLAND VA MEDICAL CENTER · 2021 · —

## Abstract

Objectives: Loss-of-function (LOF) mutations in SDHA or SDHB result in SDH-deficiency and
increase the lifetime risk for developing a number of cancers, including GI stromal tumors,
paraganglioma, pheochromocytoma, renal cell carcinoma, and breast cancer. In most cases,
tumors with these mutations arise in the setting of a heterozygous germline mutation, which is
heritable. In patients with a known pathogenic SDHA or B mutation, genetic counseling (to screen
other family members) and enhanced cancer screening procedures are indicated. When SDH-
deficient tumors are detected at early stages, they are often curable. Nonetheless, we currently
do not have the ability to identify patients at risk and screen them appropriately. The main
limitation is our lack of knowledge of the functional consequences of various SDHA or B
mutations; only SDHA or B variants that cause LOF lead to cancer. Germline variants of SDHA
and SDHB are relatively common (1.5% of population), however most are currently classified as
variants of unknown significance (VUS).
Plan: This proposal will generate novel models for functionally testing SDHA and SDHB VUS
seen in the population, including generating human model cell lines and utilizing a deep
mutational scanning approach. Human models, which can provide strong evidence to be used for
clinical classification of variants will be generated and validated for testing individual variants. In
addition, we have established a yeast model that allows functional screening of thousands of
SDHA/B mutations in the yeast homolog genes (ySdh1 and ySdh2, respectively). Using this yeast
model coupled with saturation mutagenesis, functional screening and deep sequencing, the
functional consequences of all SDHA and SDHB missense mutations will be profiled.
Methods: To fill the current void of SDH-deficient cell lines, we will use CRISPR-Cas9 to generate
SDHA- and SDHB-knockout cell lines and validate them to ensure their power for determining
clinical classifications for SDHA and SDHB VUS reported in human tumors (Aim 1). To address
the large number of SDHA and SDHB variants seen in the population, we will create libraries of
all possible ySdh1, (Aim 2) and ySdh2 (Aim 3) amino-acid variants by saturation mutagenesis
and transform these libraries into yeast models deficient in the relevant endogenous yeast protein
(e.g. mutant ySdh1 expressed in ySdh1-deleted yeast). We will select against SDHA/B LOF
variants by growing the libraries under conditions requiring fully functional SDH (glycerol media).
Following deep sequencing, depletion analysis will be performed. Functional interpretations
(functionally normal or LOF) will be made for each variant by comparing calculated effect scores
with those of nonsense/ synonymous controls.
Clinical Relevance: The care of veterans with cancer represents a significant portion of the
overall Veterans Affairs Health Care budget. It is estimated that more than 300,000 US veterans
harbor an SDHA or SDHB germline ...

## Key facts

- **NIH application ID:** 10255655
- **Project number:** 1I01BX005358-01A1
- **Recipient organization:** PORTLAND VA MEDICAL CENTER
- **Principal Investigator:** Michael C Heinrich
- **Activity code:** I01 (R01, R21, SBIR, etc.)
- **Funding institute:** VA
- **Fiscal year:** 2021
- **Award amount:** —
- **Award type:** 1
- **Project period:** 2021-04-01 → 2025-03-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10255655

## Citation

> US National Institutes of Health, RePORTER application 10255655, Functional profiling of germline SDH variants associated with cancer susceptibility (1I01BX005358-01A1). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10255655. Licensed CC0.

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