PMM2 and cystic kidney disease: However, this is also the case with the other key manifestations of hyperinsulinism and cystic kidney disease, both of which are ubiquitous in currently described PMM2-HIPKD cases but rare in PMM2-CGD (1%, and 2% of cases, respectively) (Altassan et al. 2018; Moravej et al. 2020).