The accumulation of Progerin affects several cellular functions. It is also found in healthy cells, but to a much lesser extent. In children with Progeria ten to twenty times more Progerin has been found in the nucleus.
These patients can only make an incomplete form of the protein lamin A. Healthy lamin A has an important function in the wall of the nucleus, it protects the DNA in the cell and plays a role in gene expression. Progerin, a byproduct, only has a function in the construction phase of the protein; it should be disposed of once the nucleus has been formed. However, when it accumulates in the nucleus, progerin causes problems. Patients with progeria develop many problems, including atherosclerosis and osteoporosis, they run the risk of an early stroke or heart attack.
source: Sulforaphane enhances progerin clearance in Hutchinson–Gilford progeria fibroblastst, Diana Gabriel, et al., Aging Cell - Doi:10.1111/acel.12300