PLS is caused by homozygous (2/3 of the cases) or compound heterozygous (1/3 of the cases) pathogenic variants in the gene CTSC that encodes a lysosomal cysteine protease called cathepsin C (CTSC) or dipeptidyl peptidase I (103, 104). The gene discussed is CTSC; the disease is Papillon-Lefevre disease.