In this case series of 4 young male patients with severe COVID-19, rare putative loss-of-function variants of X-chromosomal TLR7 were identified that were associated with impaired type I and II IFN responses. These preliminary findings provide insights into the pathogenesis of COVID-19.

The 4 male patients had a mean age of 26 years (range, 21-32), with no history of major chronic disease.

They were previously well before developing respiratory insufficiency due to severe COVID-19, requiring mechanical ventilation in the ICU.

The mean duration of ventilatory support was 10 days (range, 9-11); the mean duration of ICU stay was 13 days (range, 10-16). One patient died.

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