Table 1.

Subtypes of PHP and differences in phenotype, molecular genetic defects and in-vitro Gsα protein activity

	PHPIa	PPHP	PHPIb	PHPIc
AHO features	yes	yes	rarely	yes
PTH resistance	yes	no	yes	yes
GNAS defects	mutations in exons 1–13	mutations in exons 1–13	epigenetic changes at the GNAS locus e.g. loss of methylation	not known, one mutation in exon 13 (Linglart et al., 2002)
In-vitro Gsα protein activity*	diminished	diminished	normal	normal
Transmission	maternal	paternal	maternal	maternal

The classification of PHP is based on the presence or absence of AHO features and the result of the Gsα protein activity carried out on isolated Gsα from erythrocyte membranes derived from patients. The result of the Gsα protein activity assay is the only certain difference between PHPIc and PHPIa, which is diminished in PHPIa and normal in PHPIc.

^*normal range: 85–115%