SMARCA1 and urothelial carcinoma: The BAF-specific subunit gene ARID1A was identified as the by far most commonly altered subunit of SWI/SNF complexes in urothelial carcinomas (106/408 = 26%) with inactivating truncating mutations (frameshift and splice mutations resulting in premature stop codons as well as nonsense mutations) being the predominant mutational type (63% of ARID1A gene alterations) followed by alterations in the genes BRD9 (12%) and SMARCA2 (10%) (Fig 1A and 1B).