The pathogenicity of PSEN2 variants is tied to Aβ production and homology to PSEN1.

introductionThough recognized as a potential cause of autosomal dominant Alzheimer's disease, the pathogenicity of many PSEN2 variants remains uncertain. We compared amyloid beta (Aβ) production across all missense PSEN2 variants in the AlzForum database and, when possible, to corresponding PSEN1 variants.

methodsWe expressed 74 PSEN2 variants, 21 of which had known, homologous PSEN1 pathogenic variants with the same amino acid substitution, in HEK293 cells lacking presenilin 1/2. Aβ production was compared to age at symptom onset (AAO) and between PSEN1/2 homologs.

resultsAβ42/40 and Aβ37/42 ratios correlated with AAO across all PSEN2 variants, strongly driven by the subset of PSEN2 variants with PSEN1 homologs. Aβ production across PSEN1/2 homologs was highly correlated. PSEN2 AAO correlated with AAO in PSEN1 homologs but was an average of 18.3 years later. DISCUSSION: The existence of a PSEN1 homolog and patterns of Aβ production are important considerations in assessing the pathogenicity of previously reported and new PSEN2 variants. HIGHLIGHTS: There were associations between the patterns of amyloid beta (Aβ) production across presenilin 2 (PSEN2) variants and age at symptom onset (AAO). PSEN2 variants for which there is a known, corresponding variant in presenilin 1 (PSEN1) are more likely to have abnormal Aβ production patterns that strongly correlate with AAO, compared to those that lack a known PSEN1 counterpart ("non-homologous PSEN2 variants"). Most PSEN2 variants lacking PSEN1 counterparts had Aβ42/40 ratios close to those of wild-type PSN2, arguing against their pathogenicity. Homologous PSEN1 and PSEN2 variants had correlated Aβ42/40 and Aβ37/42 ratios, indicating that the corresponding amino acid substitution in each presenilin may have largely similar biochemical effects on γ-secretase processivity.