MMEL1 (membrane metalloendopeptidase like 1) encodes a metalloprotease that functions in immune modulation and disease susceptibility across multiple conditions. The protein exhibits endopeptidase activity with specificity for small peptides shorter than 3 kDa containing neutral bulky aliphatic or aromatic amino acids, sharing substrate specificity with membrane metalloendopeptidase (MME). MMEL1 demonstrates significant associations with autoimmune diseases through genetic studies. Mendelian randomization analyses identified MMEL1 as a risk factor for multiple sclerosis, with increased cerebrospinal fluid levels (OR 5.03) associated with higher disease risk 1. The gene also represents a potential therapeutic target for primary sclerosing cholangitis, where genetic inhibition may reduce disease risk 2. Additionally, MMEL1 shows associations with other autoimmune conditions including rheumatoid arthritis in Han Chinese populations 3 and hypothyroidism in primary biliary cholangitis patients 4. Single-cell analyses suggest MMEL1 plays a role in B-cell differentiation and immune cell interactions in diffuse large B-cell lymphoma 5. The gene's involvement across multiple autoimmune conditions suggests it may function as a key regulator in immune system homeostasis and inflammatory responses.