Pheochromocytomas and pituitary adenomas in three patients with MAX exon deletions

Copy number variations (CNV), an important genetic mechanism in inherited tumor genetics, can affect large genetic regions or can be limited to smaller regions within genes, such deletions of single exons. Such exon deletions can be challenging to identify and sequencing can be normal in these cases. Multiplex ligation dependent probe amplification (MLPA) can identify CNV of individual exons. Mutations in the MAX gene are associated with a risk of sporadic and hereditary pheochromocytoma. As mutations in other pheochromocytoma related genes can also cause pituitary tumors (3P-Association), we studied whether MAX exon deletions were involved in the etiology of patients with an unexplained association of multiple endocrine neoplasia including pituitary adenoma and pheochromocytoma. Using MLPA we identified three patients with pheochromocytoma and pituitary adenomas who had normal MAX sequencing but presented germline heterozygous MAX exon deletions. The three patients had either acromegaly (n=2) or prolactinoma (n=1) in association with bilateral or recurrent pheochromocytoma. Two had germline heterozygous deletions of single exons of MAX, the other had a germline heterozygous deletion of MAX exons 1-3. MAX immunohistochemical staining was lost in the pheochromocytomas of all three patients and genetic analysis confirmed loss of heterozygosity in tumor DNA. A MAX exon deletion was also transmitted from one patient to a currently asymptomatic offspring. Screening studies of pheochromocytoma patients should take into account the potential for co-existing pituitary tumors. MLPA or other techniques to identify discrete MAX exon deletions should be considered in individuals with pheochromocytoma that are negative following comprehensive sequencing.