Thus, MAO-B expression was increased in B lymphocyte cell line from male PD patients with homozygous deletion of parkin exon 433, while MAO-B activity was increased in whole brain preparations from 1 month-old male mice with homogenous deletion of parkin exon 334 and in the substantia nigra pars compacta of PD patients75. The gene discussed is PRKN; the disease is Parkinson disease.