How can people inherit polycystic kidney disease?

Genetic anomalies. Some medical conditions, including adult polycystic kidney disease, are carried in our genes and can be passed from parent to child. Generally, if one parent has pckd, their child will have a 50/50 chance of inheriting it.
From both parents. While most PKD is "autosomal dominant" meaning that only one parent has to have the gene for the child to have the disease, there is a much rarer, more severe form of pkd, "autosomal recessive." both parents must carry at least one copy of the gene to pass the disease to their offspring.
Genetic anomalies. Polycystic kidney disease in adults is an autosomal dominant disease which means that you only need abnormal gene from one parent in order to get this disease.