Aberrant splicing in the presenilin-1 intron 4 mutation causes presenile Alzheimer's disease by increased A beta 42 secretion

We previously described a splice donor site mutation in intron 4 of preseni lin-1 (PSEN1) in two patients with autopsy-confirmed early-onset Alzheimer' s disease (AD), Here we provide evidence that the intron 4 mutation is pres ent in four additional unrelated early-onset AD cases, that the mutation se gregates in an autosomal dominant manner and that all cases have one common ancestor. We demonstrate that the intron 4 mutation produces three differe nt transcripts, two deletion transcripts (Delta 4 and Delta 4(cryptic)) and one insertion transcript (ins(TAC)), by aberrant splicing, The deletion tr anscripts result in the formation of C-truncated (similar to 7 kDa) PSEN1 p roteins while the insertion transcript produces a full-length PSEN1 with on e extra amino acid (Thr) inserted between codons 113 and 114 (PSEN1 T113-11 4ins). The truncated proteins were not detectable in vivo in brain homogena tes or lymphoblast lysates of mutation carriers. In vitro HEK-293 cells ove rexpressing Delta 4, Delta 4(cryptic) or ins(TAC) PSEN1 cDNAs showed increa sed A beta 42 secretion (similar to 3.4 times) only for the insertion cDNA construct. Increased A beta 42 production was also observed in brain homoge nates, Our data indicate that in the case of intron 4 mutation, the AD path ophysiology results from the presence of the PSEN1 T113-114ins protein comp arable with cases carrying dominant PSEN1 missense mutations.