The FAH family contains two highly homologous 314 amino acid proteins, designated FAHD2A (fumarylacetoacetate hydrolase domain-containing protein 2A) and FAHD2B (fumarylacetoacetate hydrolase domain-containing protein 2A). FAHD2A and B utilize calcium and magnesium as cofactors, and may possess hydrolase activity. The genes encoding FAHD2A/B map to human chromosome 2, the second largest human chromosome, which consists of 237 million bases, encodes over 1,400 genes and makes up approximately 8% of the human genome. A number of genetic diseases are linked to genes on chromosome 2. Harlequin icthyosis, a rare and morbid skin deformity, is associated with mutations in the ABCA12 gene. The lipid metabolic disorder sitosterolemia is associated with ABCG5 and ABCG8. An extremely rare recessive genetic disorder, Alstr鰉 syndrome, is also associated with mutations to chromosome 2.