Publications by authors named "Christina Usher"

Genome-wide association studies have discovered thousands of common alleles that associate with human phenotypes and disease. Many of these variants are in non-protein-coding (regulatory) regions and are believed to affect phenotypes by modifying gene expression. In any organism with a diploid genome, such as humans, measuring the expression of each allele of a gene provides a well-controlled way to identify allelic influences on that gene's expression.

View Article and Find Full Text PDF

Many genomic segments vary in copy number among individuals of the same species, or between cancer and normal cells within the same person. Correctly measuring this copy number variation is critical for studying its genetic properties, its distribution in populations and its relationship to phenotypes. Droplet digital PCR (ddPCR) enables accurate measurement of copy number by partitioning a PCR reaction into thousands of nanoliter-scale droplets, so that a genomic sequence of interest-whose presence or absence in a droplet is determined by end-point fluorescence-can be digitally counted.

View Article and Find Full Text PDF

Most studies that have examined neuropsychological impairments associated with human immunodeficiency virus (HIV) have focused on males, yet females represent one of the largest groups of newly infected patients. Further, few studies have examined neuropsychological performance and neuroimaging outcomes among females compared to males in the modern era of highly active anti-retroviral therapy (HAART). The present study investigated neuropsychological performance and brain volumetrics among HIV+ males (n = 93) and females (n = 44) on stable HAART compared to HIV seronegative (HIV-) males (n = 42) and females (n = 49).

View Article and Find Full Text PDF

Hundreds of copy number variants are complex and multi-allelic, in that they have many structural alleles and have rearranged multiple times in the ancestors who contributed chromosomes to current humans. Not only are the relationships of these multi-allelic CNVs (mCNVs) to phenotypes generally unknown, but many mCNVs have not yet been described at the basic levels-alleles, allele frequencies, structural features-that support genetic investigation. To date, most reported disease associations to these variants have been ascertained through candidate gene studies.

View Article and Find Full Text PDF

Hundreds of genes reside in structurally complex, poorly understood regions of the human genome. One such region contains the three amylase genes (AMY2B, AMY2A and AMY1) responsible for digesting starch into sugar. Copy number of AMY1 is reported to be the largest genomic influence on obesity, although genome-wide association studies for obesity have found this locus unremarkable.

View Article and Find Full Text PDF

The incidence of HIV-associated dementia has been greatly reduced in the era of highly active antiretroviral therapy (HAART); however milder forms of cognitive impairment persist. It remains uncertain whether HAART regimens with a high degree of central nervous system penetration effectiveness (CPE) exert beneficial neurological outcomes in HIV-infected (HIV+) individuals on stable treatment. Sixty-four HIV-infected adults on HAART were assigned a CPE score using a published ranking system and divided into high (≥7; n = 35) and low (<7; n = 29) CPE groups.

View Article and Find Full Text PDF

Executive function (EF) and cognitive processing speed (CPS) are two cognitive performance domains that decline with advanced age. Reduced EF and CPS are known to correlate with age-related frontal-lobe volume loss. However, it remains unclear whether white matter microstructure in these regions is associated with age-related decline in EF and/or CPS.

View Article and Find Full Text PDF

Objective: To investigate the relationship between older age and mean cerebral white matter fiber bundle lengths (FBLs) in specific white matter tracts in the brain using quantified diffusion MRI.

Methods: Sixty-three healthy adults older than 50 years underwent diffusion tensor imaging. Tractography tracings of cerebral white matter fiber bundles were derived from the diffusion tensor imaging data.

View Article and Find Full Text PDF