 The other 10 % of cases are primarily caused by primary hyperplasia , or an increase of the number of cells . Parathyroid carcinoma accounts for less than 1 % of all cases , occurring most frequently in individuals around 50 years of age ( in stark contrast to OFC as a result of primary hyperparathyroidism ) and showing no gender preference . Approximately 95 % of hyperparatyhroidism caused by genetic factors is attributed to MEN type 1 . This mutation also tends to affect younger individuals . 
