Genetic screening for <i>TLR7</i> variants in young and previously healthy men with severe COVID-19: a case series

ABSTRACT Advanced age, male sex and chronic comorbidities are associated with severe COVID-19. However, these general risk factors cannot explain why critical illness occurs in young and apparently healthy individuals. In the past months, several publications have identified susceptibility loci and genes using comprehensive GWAS studies or genome, exome or candidate genes analysis. A recent study reported rare, loss-of-function TLR7 variants in otherwise healthy young brother pairs from two families with severe COVID-19. We aimed to prospectively study the prevalence of rare X-chromosomal TLR7 genetic variants in our cohort of young male patients with severe COVID-19. We recruited 13 patients ≤50 years who had no risk factors known to be associated with severe disease. We studied the entire TLR7 coding region and identified two missense variants (p.Asn215Ser, c.644A&gt;G and p.Trp933Arg, c.2797T&gt;C) in two out of 13 cases (15.4%). These variants were not previously reported in population control databases (gnomAD) and were predicted to be damaging by all in silico predictors. The male index patients were between 25 and 30 years old and had no apparent comorbidities. The TLR7 p.Asn215Ser co-segregated in 2 first-degree relatives severely affected by COVID-19, in a younger previously healthy the variant was found in hemizygous state, and in an older than 60 was in heterozygous state. No family members were available for testing the segregation of the p.Trp933Arg variant. These results further support that susceptibility to severe COVID-19 could be determined by inherited rare genetic variants in TLR7 . Understanding the causes and mechanisms of life-threatening COVID-19 is crucial and could lead to novel preventive and therapeutic options. This study supports a rationale for the genetic screening for TLR7 variants in young men with severe COVID-19 in the absence of other relevant risk factors. A diagnosis of TLR7 deficiency could not only inform on treatment options for the patient, but it also enables for pre-symptomatic testing of at-risk male relatives with the possibility of instituting early preventive and therapeutic interventions.