Table 4. Normality test of total mutation scores according to age of onset.

D'Agostino & Pearson omnibus normality test	Early age of onset (1–6 years)	Late age of onset (>6 years)
K2	2.128	5.659
P value	0.3451	0.059
Passed normality test (alpha = 0.05)?	Yes	Yes
P value summary	ns	ns
Skewness (S)	0.7681	1.424
SES (Standard Error of Skewness)	0.3978 (2SES = 0.7956)	0.4365 (2SES = 0.873)
Skewness Significance	No (S<2SES)	Yes (S>2SES)

Distribution analysis and normality were performed with GraphPad Prism software. Standard Error of Skewness (SES) was calculated according to [69].