To date, there are four known α subunits (α1-α4) and one β subunit. Functional GlyRs often assemble as homopentamers with five identical α subnits. From biochemical analyses, heteropentamers are predicted with either three α/β and two β/α subunits. However, recent experimental studies on structure information revealed heteromeric GlyRs have an unexpected 4:1 α : β subunit stoichiometry. Homomeric receptors are believed to be more prevalent in young animals and are mostly substituted by αβ heteromers in adults.