However, extensive genetic screening for the known mendelian mutations in APP, PSEN1, and PSEN2 for AD could not link the coarse-grained plaque to the functional impairment in one of those genes such as found for the cotton wool plaque, which is linked to an exon 9 deletion in the PSEN1 gene [10]. The gene discussed is PSEN1; the disease is Alzheimer disease.