PIGN and multiple congenital anomalies/dysmorphic syndrome: According to the clinical and laboratory findings, GPIBDs have been historically divided into two main subgroups: hyperphosphatasia with mental retardation syndrome (HPMRS) – a group of GPIBDs with elevated serum alkaline phosphatase activity (ALP) (mutations in PIGV, PGAP2, PGAP3, PIGO, PIGW, and PIGY) and multiple congenital anomalies hypotonia seizures (MCAHS) – with normal serum ALP (mutations in PIGA, PIGN, PIGT). However, the number of GPIBSDs that cannot be divided into these two groups is growing (Knaus et al., 2018).