Arylsulfatase D, also known as ARSD, is a 593 amino acid protein that localizes to the lysosome and belongs to the sulfatase family of bone and cartilage matrix proteins. Existing as three alternatively spliced isoforms which are expressed in liver, pancreas, kidney, heart, brain, lung and placenta, Arylsulfatase D uses calcium as a cofactor to catalyze reactions that are important in maintaining correct bone composition. The gene encoding Arylsulfatase D maps to human chromosome X, which contains nearly 153 million base pairs and houses over 1,000 genes. In conjunction with chromosome Y, chromosome X is responsible for sex determination. There are a number of conditions related to an abnormal number and combination of sex chromosomes, some of which include Turner's syndrome, color blindness, hemophilia and Duchenne muscular dystrophy.