HHAT is a 493 amino acid multi-pass membrane protein that localizes to the endoplasmic reticulum and belongs to the membrane-bound acyltransferase family. Expressed ubiquitously, HHAT functions to catalyze the N-terminal palmitoylation of SSH (slingshot homolog), an event that is required for SHH signaling pathways. HHAT is expressed in cancer cell lines, suggesting a role for HHAT in tumorigenesis. The gene encoding HHAT maps to human chromosome 1 and is expressed as four alternatively spliced isoforms. Chromosome 1 is the largest human chromosome, spanning about 260 million base pairs and making up 8% of the human genome. Several disorders, including Stickler syndrome, Parkinsons Disease, Gaucher disease, malignant melanoma and Usher syndrome, are caused by defects in genes that localize to chromosome 1.