Table 2.

PTH resistance differential diagnosis.

	25-OH-vitamin D levels	Kidney function	AHO	Erythrocyte Gsα activity	cAMP urinaryresponse to PTH	Multi-hormone resistance	Gene involved
iPPSD2	Normal	Normal	+	↓	↓	+	GNAS (genetic defect)
iPPSD3	Normal	Normal	±	Normal/↓	↓	±	GNAS (epigenetic defect)
iPPSD4	Normal	Normal	±	Normal	Normal	±	PRKAR1A
iPPSD5	Normal	Normal	±	Normal	Normal	±	PDE4D
Vitamin D deficiency	↓	Normal	–	n.a.	n.a.	n.a.	n.a.
Worsening of chronic kidney disease	Normal	↓	–	n.a.	n.a.	n.a.	n.a.

PTH, parathyroid hormone; AHO, Albright’s hereditary osteodystrophy; cAMP, cyclic adenosine monophosphate; iPPSD, inactivating PTH/PTHrP signalling disorder; +, present; ↓, low; ±, not alway present; -, absent; n.a., not applicable.