How Do the Porphyrias Exhibit Variable Expressivity?

How do the porphyrias exhibit variable expressivity, pleiotropy, and genetic heterogeneity? ... They are pleiotropic because they have more than one symptom. They are genetically heterogeneic because they have mutations in different genes in the porphyrin-heme pathway.

Is pleiotropy variable expressivity?

Pleiotropy is the condition whereby a single gene mutation has multiple consequences in numerous tissues. Even in the same family, two individuals carrying the same mutant genes may have different disease manifestations. Expressivity is defined as the severity of the phenotype.

What causes variable penetrance?

Variable expressivity refers to the range of signs and symptoms that can occur in different people with the same genetic condition. As with reduced penetrance, variable expressivity is probably caused by a combination of genetic, environmental, and lifestyle factors, most of which have not been identified.