Therefore, the ATA recommends that pheochromocytoma screening (by plasma or 24-hour urine fractionated metanephrines) should begin by age 8 in carriers of RET mutations associated with MEN 2B and mutated RET codons 634 and 630 and by the age 20 years in carriers of other MEN 2A RET mutations. This evidence concerns the gene RET and multiple endocrine neoplasia type 2B.