Imaging brain amyloid in nondemented young adults with Down syndrome using Pittsburgh compound B

Abstract

Down syndrome (DS) is one of the most common causes of intellectual disability. Although DS accounts for only 15% of all individuals with intellectual disabilities, adults with DS account for approximately 60% of individuals with intellectual disabilities and Alzheimer's disease. This is thought to be because of overproduction of the β-amyloid (Aβ) protein due to trisomy for the Aβ precursor protein gene on chromosome 21. Pittsburgh compound B (PiB) is a noninvasive in vivo positron emission tomography tracer used to image amyloid deposition in living humans. Studies using PiB have shown an age-dependent asymptomatic amyloid deposition in more than 20% of the cognitively normal elderly population. Presymptomatic carriers of presenilin (PS-1) and Aβ precursor protein gene mutations who are destined to develop Alzheimer's disease also show preclinical amyloid deposition. This report describes a pilot study involving the use of PiB in seven adults with DS (age: 20-44 years). Compared with objective cutoffs for amyloid positivity in older non-DS cognitively normal control subjects, only two of the seven DS subjects (age: 38 and 44 years) showed increased PiB retention. The remaining five subjects aged between 20 and 35 years showed no detectable increase in PiB retention. Interestingly, the two subjects who showed elevated PiB retention showed a striatal-predominant pattern similar to that previously reported for PS-1 mutation carriers. These results demonstrate the feasibility of conducting PiB positron emission tomography scanning in this special population, and suggest a link between Aβ overproduction and early striatal deposition of fibrillar Aβ.

Fig. 1

Pittsburgh compound B (PiB) standardized uptake value ratio images of two PiB-positive subjects with Down syndrome (DS). Axial images are shown at the top and sagittal images at the bottom. Note that the scan of subject DS-1 is very similar to those seen in late-onset Alzheimer’s disease (AD) (17), but with a predominant striatal signal. High PiB retention in subject DS-4 is mainly limited to the anterior striatum, similar to presenilin-1 mutation carriers (16).

Fig. 2

PiB standardized uptake value ratio images of five PiB-negative subjects with DS. The axial images are shown at the top and the sagittal images at the bottom. Note that all of these scans are typical of normal control subjects and show only nonspecific PiB retention in white matter.

Fig. 3

PiB retention in clinically unimpaired control subjects (red triangles), DS subjects (circles), and AD patients (blue squares). The cutoff between PiB-positive and PiB-negative for each brain region is shown by a white bar. Black diamonds demonstrate the mean ±SD for the control and AD groups. Subject DS-1 is marked with an “x” inside the circle, and subject DS-4 is marked with a filled blackcircle. Brain area abbreviations: FRC, frontal; ACG, anterior cingulate gyrus; PRC, precuneus; AVS, anterior ventral striatum; LTC, lateral temporal; PAR, parietal; MTC, mesial temporal; OCC, occipital (includes calcarine); SMC, sensorimotor; PON, pons; SWM, subcortical white matter.