SPP24, also known as secreted phosphoprotein 2, is a 211 amino acid secreted protein that belongs to the cystatin superfamily. Expressed in liver and plasma, SPP24 may play a role in coordinating an aspect of bone turnover. The gene that encodes SPP24 maps to human chromosome 2, which consists of 237 million bases encoding over 1,400 genes, making 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 syndrome is due to mutations in the ALMS1 gene. Interestingly, chromosome 2 contains what appears to be a vestigial second centromere and vestigial telomeres which gives credence to the hypothesis that human chromosome 2 is the result of an ancient fusion of two ancestral chromosomes seen in modern form today in apes.