Genetic Screening for TLR7 Variants in Young and Previously Healthy Men With Severe COVID-19

Abstract

IntroductionLoss-of-function TLR7 variants have been recently reported in a small number of males to underlie strong predisposition to severe COVID-19. We aimed to determine the presence of these rare variants in young men with severe COVID-19.MethodsWe prospectively studied males between 18 and 50 years-old without predisposing comorbidities that required at least high-flow nasal oxygen to treat COVID-19. The coding region of TLR7 was sequenced to assess the presence of potentially deleterious variants.ResultsTLR7 missense variants were identified in two out of 14 patients (14.3%). Overall, the median age was 38 (IQR 30-45) years. Both variants were not previously reported in population control databases and were predicted to be damaging by in silico predictors. In a 30-year-old patient a maternally inherited variant [c.644A>G; p.(Asn215Ser)] was identified, co-segregating in his 27-year-old brother who also contracted severe COVID-19. A second variant [c.2797T>C; p.(Trp933Arg)] was found in a 28-year-old patient, co-segregating in his 24-year-old brother who developed mild COVID-19. Functional testing of this variant revealed decreased type I and II interferon responses in peripheral mononuclear blood cells upon stimulation with the TLR7 agonist imiquimod, confirming a loss-of-function effect.ConclusionsThis 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 also enables pre-symptomatic testing of at-risk male relatives with the possibility of instituting early preventive and therapeutic interventions.

Update on human genetic susceptibility to COVID-19: susceptibility to virus and response

“…It is noteworthy the discovery of two rare and deleterious germinal variants of the TLR7 gene in two couples of young male siblings with no reported comorbidities and displaying a severe COVID-19 phenotype: the frameshift variant with maternal segregation c.2129_2132del, p.Gln710Argfs*18 and the missense variant c.2383G > T, p.Val795Phe (Table 1) [42]. The alteration of the response to type I and type II IFN subsequent to imiquimod administration, a TLR7 receptor agonist, confirmed the importance of the maintenance of TLR pathway in COVID-19 pathogenesis [42,43]. These results found confirmation in a recent independent cohort study performed in Italy, which highlighted the presence of deleterious variants of TLR7 in 2.1% of severely affected males in comparison with asymptomatic individuals [44].…”

Exploring the ethics of genetic prioritisation for COVID-19 vaccines

“…The specific effector gene in this region has recently been narrowed down to LZTFL1 , a gene with uneven distribution amongst different geographical populations, and it has been suggested that this locus could be investigated as a therapeutic target [ 8 ]. Furthermore, there is growing evidence that rare X chromosomally-located variants of TLR7 are associated with severe COVID-19 response in young men [ 13 , 14 ], and potentially constitute clinically relevant screening targets [ 15 ].…”

Why Females Do Better: The X Chromosomal TLR7 Gene-Dose Effect in COVID-19

“…Loss of function was confirmed when experiments with primary PBMCs showed no upregulation of TLR7 and a failure to induce IFN-inducible genes (ISGs) after stimulation with a TLR7 agonist ( 10 ). Later, more such cases of deleterious TLR7 variants in severe male patients have been described ( 11 , 26 , 27 ), suggesting that a loss-of-function of TLR7 could explain some cases of severe COVID-19 which result in functional defects of type 1 IFN. Likewise, single nucleotide polymorphisms (SNPs) could alter TLR7’s effectivity.…”

“…Since TLR7 is located on the X chromosome, mutations in TLR7 will affect males more than females, who bear two X chromosomes per cell. TLR7 deficiency has been reported as a genetic mediator for severe COVID-19 especially in younger males, with percentages of 1-2% found across cohorts ( 10 , 11 , 26 , 27 ). Therefore, genetic screening for TLR7 primary immunodeficiency was recommended in young males with severe COVID-19 in the absence of other relevant risk factors ( 11 , 26 , 27 ).…”

“…TLR7 deficiency has been reported as a genetic mediator for severe COVID-19 especially in younger males, with percentages of 1-2% found across cohorts ( 10 , 11 , 26 , 27 ). Therefore, genetic screening for TLR7 primary immunodeficiency was recommended in young males with severe COVID-19 in the absence of other relevant risk factors ( 11 , 26 , 27 ). Despite the observed prevalence in young males, the penetrance of deleterious TLR7 mutations may be worse in older patients, as both the pDC number and functional IFN secretion decreases with age, which was associated with a reduced number of pDCs expressing TLR7 ( 28 ).…”