Table 3.

Univariate linear and quadratic models of the relationship between CAG repeats and plasma NfL, middle frontal gyrus, medial frontal gyrus, fusiform gyrus and parahippocampal gyrus metabolic activity

Dependent variable	Group	Model	F	Adj. R2	p	AIC
NfL	A+/T+	Linear	[1, 35] = 0.30	−0.020	0.586	272.4
		Quadratic	[2, 34] = 5.45	0.198	0.009	264.4
	Isolated Aβ/non-AD	Linear	[1, 48] = 0.51	−0.010	0.476	326.8
		Quadratic	[2, 47] = 0.65	−0.014	0.525	327.9
Middle frontal gyrus	A+/T+	Linear	[1, 32] = 9.30	0.201	0.004	−76.40
		Quadratic	[2, 31] = 6.62	0.254	0.004	−77.81
	Isolated Aβ/non-AD	Linear	[1, 46] = 1.49	0.010	0.229	−129.7
		Quadratic	[2, 45] = 5.97	0.175	0.005	−137.5
Medial frontal gyrus	A+/T+	Linear	[1, 32] = 3.76	0.077	0.061	−64.38
		Quadratic	[2,31] = 5.77	0.224	0.007	−69.35
	Isolated Aβ/non-AD	Linear	[1, 46] = 0.00	−0.022	0.970	−119.2
		Quadratic	[2, 45] = 10.36	0.285	< 0.001	−135.4
Fusiform gyrus	A+/T+	Linear	[1, 32] = 4.77	0.103	0.036	−106.6
		Quadratic	[2, 31] = 3.77	0.144	0.034	−107.3
	Isolated Aβ/non-AD	Linear	[1, 46] = 0.45	−0.012	0.504	−130.1
		Quadratic	[2, 45] = 0.24	−0.033	0.788	−128.1
Parahippocampal gyrus	A+/T+	Linear	[1, 32] = 5.75	0.126	0.022	−94.51
		Quadratic	[2, 31] = 11.35	0.423	< 0.001	−105.6
	Isolated Aβ/non-AD	Linear	[1, 46] = 0.45	−0.012	0.503	−156.7
		Quadratic	[2, 45] = 1.49	0.020	0.236	−157.3

Metrics of the linear and quadratic models (F-statistics with degrees of freedom, adjusted R², and p-values) are reported, with significance set at p < 0.05. Bold text indicates the models that best fit the relationship between CAG repeats and the dependent variables