This was later substantiated by a homozygous loss-of-function mutation (S276C) identified as motor neurodegeneration 2 (mnd2) in mice (Jones et al., 2003), which was further bolstered by the development of homozygous HTRA2 knock-out mice exhibiting Parkinsonian phenotype (Martins et al., 2004) thus assigning HTRA2 gene the PARK13(Parkinson’s disease 13) locus (Strauss et al., 2005; Abou-Sleiman et al., 2006). Here, HTRA2 is linked to Young adult-onset Parkinsonism.