Tractography of the Corpus Callosum in Huntington's Disease

This entry covers the brain MRI cohort of a cross-sectional diffusion study by the IRCCS Santa Lucia Foundation in Rome and the IRCCS Neuromed in Pozzilli, Italy. The study traced the corpus callosum in each subject, split it into seven tracts by their cortical target region, and compared diffusion measures between people with the Huntington's disease mutation before and after symptom onset and healthy controls. The images are not public. The PLOS figshare record linked to the paper contains only two supplementary tables, one with intra-rater reliability values and one with group-level tract measures.

Composition

The paper reports 100 participants: 25 gene carriers without manifest symptoms, 25 patients with manifest Huntington's disease, and 50 healthy controls recruited from the community. Mutation carriers had a confirmed CAG repeat expansion, and presymptomatic status meant a UHDRS total motor score below 5 with normal cognitive and behavioural assessment. Patients in advanced stages, and people with brain injury or focal lesions, were excluded. Table 1 gives the sex split per group and the mean age, which was about 37 years in the presymptomatic group, 47 in patients and 43 in controls.

Acquisition

All scans were acquired in one session on a 3 T Siemens Allegra scanner with a birdcage head coil. The protocol had axial proton density and T2-weighted dual turbo spin echo, axial FLAIR, a sagittal 3D T1-weighted MDEFT at 1 mm isotropic resolution, and spin echo EPI diffusion imaging with 30 directions at b = 1000 s/mm2 and 1.8 mm isotropic voxels, repeated three times to raise the signal-to-noise ratio.

Annotations

One rater, blinded to group, age and sex, drew the tractography regions of interest on colour FA maps in TrackVis. Only group-level tract volumes and FA, AD and RD values are released.

Known limitations

• MRI images and tractography results are not shared, and no terms for them are published.
• Table 1 lists the control group as n = 25 in its header while its sex counts add up to 50, the number given in the abstract and the methods.
• Subjects with excessive head movement were excluded, but the paper does not say how many.
• Age is reported only as group mean and standard deviation.