Study of factors influencing susceptibility and age at onset of type 1 diabetes: A review of data from Continental Italy and Sardinia

AIM: To investigate the role of protein tyrosin phosphatase
22 (PTPN22), maternal age at conception and
sex on susceptibility and age at onset of type 1 diabetes
(T1D) in Continental Italy and Sardinian populations.
METHODS: Three hundred seventy six subjects admitted
consecutively to the hospital for T1D and 1032
healthy subjects as controls were studied in Continental
Italy and 284 subjects admitted consecutively to
the hospital for T1D and 5460 healthy newborns were
studied in Sardinia. PTPN22 genotype was determined
by DNA analysis. Maternal age at conception and age
at onset of disease were obtained from clinical records.
χ 2 test of independence, student t test for differences
between means and odds ratio analysis were
carried out by SPSS programs. Three way contingency
table analysis was carried out according to Sokal and
Rohlf.
RESULTS: The pattern of association between PTPN22
and T1D is similar in Continental Italy and Sardinia:
the proportion of *T allele carriers is 13.6% in T1D vs
6.7% in controls in Continental Italy while in Sardinia
is 7.3% in T1D vs 4.4% in controls. The association
between T1D and maternal age at conception is much
stronger in Sardinia than in Italy: the proportion of
newborn from mother aging more than 32 years is
89.3% in T1D vs 32.7% in consecutive newborn in
Sardinia (P < 10-6) while in Continental Italy is 32.2%
in T1D vs 19.1% in consecutive newborns (P = 0.005).
This points to an important role of ethnicity. A slight
prevalence of T1D males on T1D females is observed
both in Continental Italy and Sardinia. PTPN22 genotype
does not exert significant effect on the age at
onset neither in Continental Italy nor and Sardinia. Maternal
age does not influence significantly age at onset
in Italy (8.2 years in T1D infants from mothers aging
32 years or less vs 7.89 years in T1D infants from
mothers aging more than 32 years: P = 0.824) while
in Sardinia a border line effect is observed (5.75 years
in T1D infants from mothers aging 32 years or less vs
7.54 years in T1D infants from mothers aging more
than 32 years: P = 0.062). No effect of sex on age at
onset is observed in Continental Italy while in Sardinia
female show a lower age at onset of T1D as compared
to males (8.07 years in males vs 6.3 years in females:
P = 0.002).
CONCLUSION: The present data confirm the importance
of ethnicity on susceptibility and on the age at
onset of T1D.