This transmission pattern is likely modified by the effects of imprinting which also can modify the phenotype. Mutltigenerational family patterns have an excess of maternal transmission. The full phenotype is more likely expressed among maternally transmitted cases whereas partial or incomplete expression is more often seen among individuals who received the paternal allele.
Heterozygous muttions in the GNAS1 gene (20q13.32) plays a role in this disease. Signal transduction failure likely plays a major role in the failure of organs to respond to the appropriate hormone.
Several subtypes of pseudohypoparathyroidism have been reported but some do not have ocular signs. However, type 1C (612462) patients can have cataracts and nystagmus with an almost identical phenotype to that of IA and may be the same condition.