Table 1:

Demographic and clinical characteristics of the study cohort

Variable	n	Age, Mean ± SD, y	Head Circumference, Mean ± SD, cm	Clinical Severity Scores, Mean ± SD
Variable	n	Age, Mean ± SD, y	Head Circumference, Mean ± SD, cm	Total	Head Growth	Seizures	Respiratory Irregularities	Scoliosis	Gait Abnormalities
All RTT subjects	22	8.6 ± 1.8	49.5 ± 2.1	7.8 ± 2.4	2.5 ± 0.8	1.2 ± 1.0	1.7 ± 0.8	0.7 ± 1.0	1.6 ± 1.0
Affected MZ twin		8.4	50.5	8	3	1	2	0	2
More severe (gait criterion)	12	8.8 ± 1.6	49.3 ± 2.4	9.6 ± 1.3^*	2.6 ± 0.7	1.4 ± 1.0	1.8 ± 0.8	1.7 ± 1.2^*	2.4 ± 0.7^*
Less severe (gait criterion)	10	8.3 ± 2.1	49.4 ± 1.8	5.9 ± 1.5	2.5 ± 1.0	1.0 ± 1.1	1.6 ± 0.8	0.1 ± 0.3	0.7 ± 0.7
Control subjects	25	8.9 ± 1.9

Note:—RTT indicates Rett syndrome; MZ, monozygotic. Age represents age at time of MR imaging scan. The maximum total clinical severity score is 15. The “more severe” group included the following mutations: R106W (n = 1), T158M (n = 3), R255X (n = 1), R270X (n = 2), R294X (n = 2), and C-terminal deletions (n = 3). The “less severe” group included the following mutations: R133C (n = 1), R168X (n = 1), R255X (n = 1), R294X (n = 4), R306C (n = 2), and G451T/D151Y (n = 1 each).
* P < .05 when comparing more severe versus less severe gait.