Dopamine receptor D4 (DRD4) polymorphisms with reduced functional potency intensify atrophy in syndrome-specific sites of frontotemporal dementia.

OBJECTIVE: We aimed to understand the impact of dopamine receptor D4 (DRD4) polymorphisms on neurodegeneration in patients with dementia. We hypothesized that DRD4dampened-variants with reduced functional potency would be associated with greater atrophy in regions with higher receptor density. Given that DRD4 is concentrated in anterior regions of the limbic and cortical forebrain we anticipated genotype effects in patients with a more rostral pattern of neurodegeneration. METHODS: 337 subjects, including healthy controls, patients with Alzheimer's disease (AD) and frontotemporal dementia (FTD) underwent genotyping, structural MRI, and cognitive/behavioral testing. We conducted whole-brain voxel-based morphometry to examine the relationship between DRD4 genotypes and brain atrophy patterns within and across groups. General linear modeling was used to evaluate relationships between genotype and cognitive/behavioral measures. RESULTS: DRD4 dampened-variants predicted gray matter atrophy in disease-specific regions of FTD in anterior cingulate, ventromedial prefrontal, orbitofrontal and insular cortices on the right greater than the left. Genotype predicted greater apathy and repetitive motor disturbance in patients with FTD. These results covaried with frontoinsular cortical atrophy. Peak atrophy patterned along regions of neuroanatomic vulnerability in FTD-spectrum disorders. In AD subjects and controls, genotype did not impact gray matter intensity. CONCLUSIONS: We conclude that DRD4 polymorphisms with reduced functional potency exacerbate neuronal injury in sites of higher receptor density, which intersect with syndrome-specific regions undergoing neurodegeneration in FTD.

PHOG, a candidate gene for involvement in the short stature of Turner syndrome.

The abnormalities seen in Turner syndrome (monosomy X) presumably result from haploinsufficiency of certain genes on the X chromosome. Gene dosage considerations lead to the prediction that the culpable genes escape X inactivation and have functional homologs on the Y chromosome. Among the genes with these characteristics are those residing in the pseudoautosomal regions (PAR) of the sex chromosomes. A pseudoautosomal location for a dosage-sensitive locus involved in stature has been suggested based on the analyses of patients with deletions of a specific segment of the short arm PAR; hemizygosity for this putative locus probably also contributes to the short stature in Turner individuals. We have isolated a gene from the critical deleted region that encodes a novel homeodomain-containing transcription factor and is expressed at highest levels in osteogenic cells. We have named the gene PHOG, for pseudoautosomal homeobox-containing osteogenic gene. Its deletion in patients with short stature, the predicted altered dosage in 45,X individuals, along with the nature of the encoded protein and its expression pattern, make PHOG an attractive candidate for involvement in the short stature of Turner syndrome. We have also found that the mouse homolog of PHOG is autosomal, which may help to explain the lack of a growth abnormality in mice with monosomy X.