The g.~6.7kbdel (p.Ex9_11del; c.914_1199+1del; CA251545) in PAH is a large deletion involving exons 9, 10, and 11. The deletion removed exons 9-11 but spared exon 12 in long-range PCR (see PMID: 10472529). This region is critical to protein function, as exons 9 and 10 form part of the PAH catalytic domain, and include key amino acid residues. Therefore, this is a multi-exon deletion that disrupts the reading frame and is NOT predicted to undergo NMD, which truncates/alters a critical region for protein function. Thus, PVS1_Strong is applied. It is absent from ethnically diverse control databases, including gnomAD/ExAC, 1000 Genomes, and ESP (PM2). It has been previously reported in one case with mild PKU (per abnormal blood Phe levels; BH4 deficiency does not appear to have been formally excluded) (PP4), in confirmed trans with the p.E390G variant (Likely Pathogenic per PAH VCEP) (PMID: 10472529) (PM3). Classification: Likely Pathogenic Supporting Criteria: PVS1_Strong; PM2; PM3; PP4