The human genetic basis of tuberculosis (TB) has long remained elusive. We recently reported a high level of enrichment in homozygosity for the common TYK2 P1104A variant in a heterogeneous cohort of patients with TB from non-European countries in which TB is endemic. This variant is homozygous in ∼1/600 Europeans and ∼1/5,000 people from other countries outside East Asia and sub-Saharan Africa. We report a study of this variant in the UK Biobank cohort. The frequency of P1104A homozygotes was much higher in patients with TB (6/620, 1%) than in controls (228/114,473, 0.2%), with an odds ratio (OR) adjusted for ancestry of 5.0 [95% confidence interval (CI): 1.96-10.31, P = 2 × 10 −3 ]. Conversely, we did not observe enrichment for P1104A heterozygosity, or for TYK2 I684S or V362F homozygosity or heterozygosity. Moreover, it is unlikely that more than 10% of controls were infected with Mycobacterium tuberculosis, as 97% were of European genetic ancestry, born between 1939 and 1970, and resided in the United Kingdom. Had all of them been infected, the OR for developing TB upon infection would be higher. These findings suggest that homozygosity for TYK2 P1104A may account for ∼1% of TB cases in Europeans.T uberculosis (TB) remains a major global public health problem. About a quarter of the world's population is infected with Mycobacterium tuberculosis (1, 2), resulting in ∼10 million new cases and 1.6 million deaths worldwide in 2017 (3). Nevertheless, only ∼5% of infected individuals develop active TB in their lifetime (1,4). Abundant evidence for the existence of a genetic component of TB in humans has accumulated from classic genetics studies performed from the turn of the 20th century onward, but its molecular architecture has long remained elusive (5-9). From 1996 onward, single-gene inborn errors of IFN-γ immunity have been found to underlie Mendelian susceptibility to mycobacterial disease (MSMD), which is characterized by severe disease caused by poorly virulent mycobacteria (bacillus Calmette-Guérin vaccines and environmental mycobacteria) (10-15). The clinical penetrance for MSMD depends on the genetic etiology and is inversely correlated with the levels of residual IFN-γ immunity (16). From 2001 onward, autosomal recessive interleukin-12 receptor β1 (IL-12Rβ1) and tyrosine kinase 2 (TYK2) deficiencies have also been identified in children with severe TB and without MSMD (17-23). These two deficiencies impair both the IL-12-and IL-23-dependent production of IFN-γ. They are caused by very rare (minor allele frequency, MAF <5 × 10 −5 worldwide) or private loss-of-function alleles.We recently discovered a strong enrichment in homozygosity for the common TYK2 missense variant P1104A in a genetically heterogeneous cohort of patients with TB from countries outside of Europe in which this disease is endemic, relative to ancestryadjusted controls, with an odds ratio (OR) of 89.3 (95% CI, 14.7-1,725, P = 8.37 × 10 −8 ) (24). Homozygosity for P1104A is also a genetic etiology of MSMD, albeit with much lower estimate...