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

Table 1 Distribution of protein tyrosin phosphatase 22 genotypes in type 1 diabetes and controls in Continental Italy and in Sardinia

	% Proportion of *T allele carriers	Total n
T1D
Continental Italy	13.60%	376
Controls	6.70%	1032
T1D
Sardinia	7.30%	248
Controls	4.40%	205

T1D: Type 1 diabetes.

Table 2 Maternal age at conception in consecutive newborns and in children with type 1 diabetes in Continental Italy and in Sardinia

	Sardinia		Continental Italy
	Consecutive newborns	Children with T1D	Consecutive newborns	Children with T1D
% proportion with maternal age > 32 yr	32.70%	89.30%	19.10%	32.20%
Total n	5460	187	792	90
χ2 test of independence
χ2	253.705		7.821
df	1		1
P	< 10-6		0.005
OR analysis
OR	17.191		2.018
95%CI	10.569-24.396		1.234-3.331

Three way contingency table analysis by a log linear model: x = T1D vs controls; y = maternal age (≤ 32 yr vs > 32 yr); z = Continental Italy vs Sardinia. x, y and z interaction: G = 45.703; df = 1; P < 0.0001. T1D: Type 1 diabetes.

Table 3 Effect of protein tyrosin phosphatase 22 genotype on age at onset of type 1 diabetes

	Continental Italy	Sardinia
	Age at onset (yr)
	mean ± SE	mean ± SE
PTPN22 genotype
*C/*C	8.56 ± 0.28	7.44 ± 0.32
*T carriers	9.85 ± 1.03	7.43 ± 1.33
Student t test for differences between means
	P = 0.100	P = 0.540

Table 4 Maternal age (year) at conception and age at onset of diabetes

		Age at onset of diabetes (yr)			t test for differences between means
		mean	SE	total n
Sardinia	Maternal age ≤ 32	5.75	0.89	20
	Maternal age > 32	7.54	0.31	169	P = 0.062
Continental Italy	Maternal age ≤ 32	8.02	0.51	61
	Maternal age > 32	7.89	0.81	28	P = 0.894

Age at onset; Sardinia vs Continental Italy. t test for differences between means. Maternal age > 32, P = 0.720; Maternal age ≤ 32, P = 0.028.

Table 5 Effect of sex on the age at onset of type 1 diabetes

	Continental Italy	Sardinia
	Age at onset (yr)
	mean ± SE	mean ± SE
Sex
Males	8.50 ± 0.39	8.07 ± 0.40
Females	8.93 ± 0.39	6.30 ± 0.40
Student t test for differences between means
	P = 0.433	P = 0.002