Potential explanations include: 1) another germ line APC mutation in linkage disequilibrium with c.3920T>A in some or all Ashkenazi patients with multiple colorectal neoplasms, 2) a tendency for the c.3920T>A allele to undergo slippage in some patients more than in others, and 3) patient study groups have had an additional, uncharacterized tendency to form colorectal tumours. Here, APC is linked to colorectal neoplasm.