Investigation of Brain Nitrogen in Partial Ornithine Transcarbamylase Deficiency (OTCD) Using 1 H MRS, DTI, and fMRI

Concentration based on area under curve on 1H Magnetic Resonance Spectroscopy(MRS) and quantitated by LCModel (a method that allows automatic quantitation of spectroscopy data). A metabolite's tissue concentration is related to the integrated amplitude, the area under the curve of the MRS signal, it produces. While MRS signals are usually acquired in the time domain as free induction decays or echoes, they are usually viewed and analyzed in the frequency domain. The frequency domain representation is derived from the acquired time domain data by the Fourier Transform. The protocol we use selects 257 averages. The machine summates the data at each time point to generate one value for the area under the curve. Therefore, we don't have the measurement at each time point. Furthermore, we measured voxels in two different brain areas containing different kinds of brain matter: one voxel was located in posterior cingulate gray matter (PCGM) and the other in parietal white matter (PWM).

Time frame: Baseline

Population: Two OTCD patients and one healthy control were excluded due to excessive head motion.

Fractional Anisotropy (FA) is a measure of the diffusion asymmetry within a voxel as defined by its eigenvalues. In our study, FA is being used as a measure of white matter integrity, because FA is very sensitive to small microstructural changes.Fractional anisotropy (FA) is a scalar value between zero and one (0-1) that describe anisotropy of a diffusion process. A value of zero means that diffusion is isotropic, i.e. it is unrestricted (or equally restricted) in all directions. A value of one means that diffusion occurs only along one axis and is fully restricted along all other directions.

Time frame: Baseline

Investigation of differences in functional connectivity of OTCD patients compared to healthy controls, particularly in the default-mode network (DMN) and the set-maintenance network (SMN). Participants underwent a resting-state scan using 3T fMRI. Combining independent component analysis (ICA) and region-of-interest (ROI) analyses, identified the nodes that comprised each network in each group, and assessed internodal connectivity. For each subject, this analysis generated a correlation value, which reflected the strength of functional connectivity between each ROI pair.The correlation r-values were normalized using Fisher's r-to-Z-transform, generating z-scores. The DMN was composed of 1) anterior cingulate/medial prefrontal cortex (ACC/mPFC), 2) posterior cingulate cortex (PCC), and 3) bilateral inferior parietal lobule (IPL). The SMN was composed of 1)ACC, 2) bilateral superior frontal gyrus (SFG), and 3) bilateral anterior insula/frontal operculum (aI/fO).

Time frame: Baseline

Population: Resting state data was not acquired for several of our participants (7 controls and 4 patients). Furthermore, 3 OTCD patients were excluded from the analyses due to excessive head motion.

Testing consisted of the Wechsler Abbreviated Scale of Intelligence (WASI), Comprehensive Trail Making Test (CTMT) (range 17-87), and the Behavioral Rating Inventory of Executive Function (BRIEF) (range GEC: 70-210; BRI:39-82 ; MI:41-92). The WASI includes three measures of intelligence; including, performance IQ (sum of block design and matrices sub scales; range: 40-160), verbal IQ (sum of vocabulary and similarities sub scales; range 40-160), and total IQ (sum of all four subscales; range: 80-320). The CTMT measures simple attention and executive function, it consists of five dot to dots that increase with complexity and difficulty. Higher values indicate better outcomes for all scales.

Time frame: Baseline