Clinical measurement of cellular DNA damage hypersensitivity in patients with DNA repair defects

Ola Hammarsten,Olov Ekwall,Pegah Johansson,Emilie Wahren Borgström,Torben Ek,Sara Cajander,C I Edvard Smith,Anna Lyytikäinen,Sofia Thunström,Anders Fasth

doi:10.1186/s13023-022-02199-8

Abstract

BackgroundDNA repair deficiency disorders are rare inherited diseases arising from pathogenic (disease-causing) variants in genes involved in DNA repair. There are no standardized diagnostic assays for the investigation of pathological significance of unknown variants in DNA repair genes. We hypothesized that our assays for measuring in vitro patient blood cell hypersensitivity to DNA-damaging agents can be used to establish the pathological significance of unknown variants in DNA repair genes. Six patients with variants in the DNA repair genes PRKDC (two siblings), DCLRE1C (two siblings), NBN, and MSH6 were included. Here, we used the cell division assay (CDA) and the γ-H2AX assay, which were both developed and clinically validated by us, to measure patient cell hypersensitivity in response to ionizing radiation, mitomycin C, cytarabine and doxorubicin.ResultsRadiation hypersensitivity was detected in the two patients with variants in the PRKDC gene (p < 0.0001 for both at 3.5 Gy), and the two patients with DCLRE1C variants (p < 0.0001 at 3.5 Gy for sibling 1 and p < 0.0001 at 1 Gy for sibling 2). The cells from the patients with the PRKDC variant were also deficient in removing γ-H2AX (p < 0.001). The cells from the patient with variants in the NBN gene were hypersensitive to mitomycin C (p = 0.0008) and deficient in both induction and removal of γ-H2AX in response to radiation.ConclusionsThe combination of the CDA and the γ-H2AX assay is useful in investigating the significance of unknown variants in some DNA repair genes.

Highlights

DNA repair deficiency disorders are rare inherited diseases arising from pathogenic variants in genes involved in DNA repair
As some patients with DNA repair defects are sensitive to specific types of DNA damage, patient cell sensitivity to different DNA-damaging agents may be a way to examine the functional deficiency of unknown variants in the DNA repair gene
The mean T cell proliferation in the untreated samples was lower than the Hammarsten et al Orphanet Journal of Rare Diseases (2022) 17:50 Table 1 Summary of patient-cell sensitivity to different agents using the cell division assay (CDA) and γ-H2AX assays

Summary

Introduction

DNA repair deficiency disorders are rare inherited diseases arising from pathogenic (disease-causing) variants in genes involved in DNA repair. We hypothesized that our assays for measuring in vitro patient blood cell hypersensitivity to DNA-damaging agents can be used to establish the pathological significance of unknown variants in DNA repair genes. DNA repair deficiency disorders are rare monogenic diseases caused by variants in the genes coding for proteins involved in DNA damage response and repair. These diseases may share some clinical features, such as growth retardation, neurological defects, premature ageing, skin alterations, telangiectasia, and xerosis cutis [1]. We have developed the cell division assay (CDA) to measure the relative sensitivity of patient cells to DNA-damaging agents in vitro [6]. We have validated the assay using patients with variants of known clinical significance [6, 7]

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Results

Conclusion