SEZ6L (seizure related 6 homolog-like) is a 1,024 amino acid single-pass type I membrane protein that localizes to the endoplasmic reticulum. Widely expressed, SEZ6L is a candidate tumor suppressor gene and may contribute to specialized endoplasmic reticulum functions in neurons. SEZ6L contains three CUB domains and five sushi (CCP/SCR) domains, which may be involved in protein-protein interactions and signal transduction. The gene encoding SEZ6L is located on human chromosome 22, which houses over 500 genes and is the second smallest human chromosome. Mutations in several of the genes that map to chromosome 22 are involved in the development of Phelan-McDermid syndrome, Neurofibromatosis type 2, autism and schizophrenia.