Non-insulin-dependent diabetes mellitus (NIDDM) is known to have a str
ong genetic basis, but the mode of inheritance is still unknown. Recen
t studies have suggested that maternal inheritance is important; this
complicates the transmission pattern of NIDDM. In our study, the famil
ial aggregation of diabetes and the maternal effect were investigated
through three generations. The CODIAB Study recruited 536 NIDDM patien
ts between 35 and 74 years of age from 10 diabetes centers in France.
Familial aggregation was confirmed: among 218 NIDDM patients, 66% had
at least one diabetic relative. Mothers were implicated 2 times more f
requently than fathers (P < 0.001). This maternal effect was confirmed
because more diabetic cases were noted among maternal than paternal a
unts and uncles (P < 0.02). When we considered the next generation, wo
men had more diabetic offspring than men (P < 0.01). Other factors sus
ceptible to modify the familial aggregation were considered. The mater
nal effect was not significantly related to the patients' ages (P > 0.
2). The genetic component was more important when the diagnosis was ma
de earlier, but the maternal effect was homogeneous (P > 0.3). In conc
lusion, we found a familial aggregation of diabetes that suggests a st
rong genetic component with a mode of inheritance that may be influenc
ed by a maternal environment.