Any familial isolated hyperparathyroidism in which the cause of the disease is a mutation in the GCM2 gene. The disease is hyperparathyroidism 4 (MONDO_0024570, a Monarch Disease Ontology identifier). Also known as: GCM2 familial isolated hyperparathyroidism, familial isolated hyperparathyroidism caused by mutation in GCM2, hyperparathyroidism type 4.