Cystine kidney stones account for less than 1% of all stones. They are usually made of pure cystine (a sulfur-containing amino acid). Type V stones present themselves in two distinct forms named Type Va (the most common one) and type Vb. Type Va stones are about ten times more frequent than type Vb stones. Because the treatment for Cystine stones is urine alkalization, some 5-10% of individuals with recurrent stones end up forming calcium phosphate kidney stones (mainly in the form of carbapatite or ACCP).