Expression defect size among unclassified MLH1 variants determines pathogenicity in Lynch syndrome diagnosis

TY - JOUR

T1 - Expression defect size among unclassified MLH1 variants determines pathogenicity in Lynch syndrome diagnosis

AU - Hinrichsen, Inga

AU - Brieger, Angela

AU - Trojan, Jörg

AU - Zeuzem, Stefan

AU - Nilbert, Mef

AU - Plotz, Guido

PY - 2013/5/1

Y1 - 2013/5/1

N2 - Purpose: Lynch syndrome is caused by a germline mutation in a mismatch repair gene, most commonly the MLH1 gene. However, one third of the identified alterations are missense variants with unclear clinical significance. The functionality of these variants can be tested in the laboratory, but the results cannot be used for clinical diagnosis. We therefore aimed to establish a laboratory test that can be applied clinically. Experimental Design: We assessed the expression, stability, and mismatch repair activity of 38 MLH1 missense variants and determined the pathogenicity status of recurrent variants using clinical data. Results: Four recurrent variants were classified as neutral (K618A, H718Y, E578G, V716M) and three as pathogenic (A681T, L622H, P654L). All seven variants were proficient in mismatch repair but showed defects in expression. Quantitative PCR, pulse-chase, and thermal stability experiments confirmed decreases in protein stability, which were stronger in the pathogenic variants. The minimal cellular MLH1 concentration for mismatch repair was determined, which corroborated that strongly destabilized variants can cause repair deficiency. Loss of MLH1 tumor immunostaining is consistently reported in carriers of the pathogenic variants, showing the impact of this protein instability on these tumors. Conclusions: Expression defects are frequent among MLH1 missense variants, but only severe defects cause Lynch syndrome. The data obtained here enabled us to establish a threshold for distinguishing tolerable (clinically neutral) from pathogenic expression defects. This threshold allows the translation of laboratory results for uncertain MLH1 variants into pathogenicity statements for diagnosis, thereby improving the targeting of cancer prevention measures in affected families.

AB - Purpose: Lynch syndrome is caused by a germline mutation in a mismatch repair gene, most commonly the MLH1 gene. However, one third of the identified alterations are missense variants with unclear clinical significance. The functionality of these variants can be tested in the laboratory, but the results cannot be used for clinical diagnosis. We therefore aimed to establish a laboratory test that can be applied clinically. Experimental Design: We assessed the expression, stability, and mismatch repair activity of 38 MLH1 missense variants and determined the pathogenicity status of recurrent variants using clinical data. Results: Four recurrent variants were classified as neutral (K618A, H718Y, E578G, V716M) and three as pathogenic (A681T, L622H, P654L). All seven variants were proficient in mismatch repair but showed defects in expression. Quantitative PCR, pulse-chase, and thermal stability experiments confirmed decreases in protein stability, which were stronger in the pathogenic variants. The minimal cellular MLH1 concentration for mismatch repair was determined, which corroborated that strongly destabilized variants can cause repair deficiency. Loss of MLH1 tumor immunostaining is consistently reported in carriers of the pathogenic variants, showing the impact of this protein instability on these tumors. Conclusions: Expression defects are frequent among MLH1 missense variants, but only severe defects cause Lynch syndrome. The data obtained here enabled us to establish a threshold for distinguishing tolerable (clinically neutral) from pathogenic expression defects. This threshold allows the translation of laboratory results for uncertain MLH1 variants into pathogenicity statements for diagnosis, thereby improving the targeting of cancer prevention measures in affected families.

U2 - 10.1158/1078-0432.ccr-12-3299

DO - 10.1158/1078-0432.ccr-12-3299

M3 - Tidsskriftartikel

SN - 1078-0432

VL - 19

SP - 2432

EP - 2441

JO - Clinical Cancer Research

JF - Clinical Cancer Research

IS - 9

ER -