Psoriasis is believed to be a genetic disease, though researchers do not completely understand how psoriasis is passed from one generation to another. The pattern of inheritance probably involves multiple genes or combinations of many genes, and the search is on to find those genes.
About one out of three people with psoriasis report that a relative has or had psoriasis. If one parent has psoriasis, a child has about a 25 percent chance of having psoriasis. If both parents have psoriasis, a child has approximately a 65 percent chance of being diagnosed with the disease. For a family with a child that already has psoriasis, the chance of a second child having psoriasis is 51 percent if one parent has psoriasis, but if both parents have the disease, then the chance of a second child having psoriasis is 83 percent.
Studies of identical twins with psoriasis show that psoriasis is at least partially genetic. But those same studies also reinforce the complexity of psoriasis. In about one-third of identical twins where psoriasis is present, only one twin has the disease, indicating that environmental factors or triggers play a role in who develops psoriasis. The theory that psoriasis is triggered by a combination of genes and external forces is called "multifactorial inheritance." Once the genes responsible for psoriasis are discovered, the inheritance pattern may be better understood.
Safety of Treatments
Many doctors recommend women avoid psoriasis treatments altogether or use only the safest forms, which include certain topicals and UVB phototherapy, during conception, pregnancy and nursing. Each psoriasis medication has a different set of precautions, so it is important to work with your doctor to determine what treatment is appropriate for you during pregnancy.
When pregnancies are planned, women may want to time treatments so only minimal treatment is required during pregnancy. For example, a woman who experiences remissions that average one year following a course of PUVA can plan to finish their most recent course before attempting conception.
Be sure to talk to your doctor about your treatment plan if you intend to become pregnant. Men also should limit their psoriasis treatments if pregnancy is on the horizon.
Most systemic medications should be stopped before trying to conceive. Methotrexate is capable of causing miscarriages or fetal malformations. Both men and women should discontinue using methotrexate at least 12 weeks before trying to conceive.
It is unknown if biologics are safe to take before or during pregnancy. Retinoids like Tazorac, Soriatane and isotretinoin have been linked to birth defects and should be stopped before trying to become pregnant.