Table 4.

MRI metrics analyzed with respect to functional disability score for individuals with PLP1 mutations. A generalized linear model (GLM) analyses based on the GEE (generalized estimating equation) methodology was performed with FDS subgroups as the main effect term and age as a covariate to test FDS subgroup differences (JMP; SAS Institute Inc.). The total brain volume (TBV) was used as an additional covariate when comparing white matter volume and the corpus callosum area. The statistical results of the GLM analyses were based on the “Chi-Square” statistics and associated p-values. P-values of 0.05 or less were considered significant. Since all three measurements were not performed on all subjects, a median split for each measure was conducted.

	Lower FDS group†	Higher FDS group†	Chi Square (p-value)
	FDS < 21	FDS ≥ 21
Sample size	21	24
Age (years)	16.5 ± 13.3	31.4 ± 15.6
White matter volume (cm3)	69.5 ± 42.3	112.8 ± 40.1
Total brain volume (cm3)	188.4 ± 76.7	253.1 ± 80.3
WM fraction (%)	34.8 ± 9.5	43.6 ± 7.1	9.83 (p = 0.0017)**
	FDS < 18	FDS ≥ 18
Sample size	25	27
Age (years)	12.7 ± 14.1	27.2 ± 15.5
Inter-caudate distance (cm)	1.47 ± 0.63	1.32 ± 0.46
Transverse width of inner skull table (cm)	13.2 ± 4.7	13.5 ± 3.3
ICD/TWS	0.111 ± 0.027	0.097 ± 0.016	6.28 (p = 0.012)**
	FDS < 20	FDS ≥ 20
Sample size	17	18
Age (years)	16.0 ± 15.1	25.5 ± 14.6
Corpus callosum area (cm2)	2.73 ± 0.75	4.30 ± 1.68	7.52 (p = 0.0061)*

^†Mean values ± 1SD.

^*With TBV and age as covariates.

^**With age as a covariate.