There are a number of causes for hypercalcemia with decreased PTH including malignancies, over intoxication with calcium and vitamin D or vitamin V to sarcoidosis, etc. For a comprehensive list please see Etiology of hypercalcemia—UpToDate (Shane et al. n.d., https://www.uptodate.com/contents/etiology-of-hypercalcemia). This evidence concerns the gene PTH and Hypercalcemia.