ABCA7 loss-of-function variants, expression, and neurologic disease risk.

OBJECTIVE: To investigate and characterize putative "loss-of-function" (LOF) adenosine triphosphate-binding cassette, subfamily A member 7 (ABCA7) mutations reported to associate with Alzheimer disease (AD) risk. METHODS: We genotyped 6 previously reported ABCA7 putative LOF variants in 1,465 participants with AD, 381 participants with other neuropathologies (non-AD), and 1,043 controls and assessed the overall mutational burden for association with different diagnosis groups. We measured brain ABCA7 protein and messenger RNA (mRNA) levels using Western blot and quantitative PCR, respectively, in 11 carriers of the 3 most common variants, and sequenced all 47 ABCA7 exons in these participants to screen for other coding variants. RESULTS: At least one of the investigated variants was identified in 45 participants with late-onset Alzheimer disease, 12 participants with other neuropathologies, and 11 elderly controls. Association analysis revealed a significantly higher burden of these variants in participants with AD (p = 5.00E-04) and those with other neuropathologies (p = 8.60E-03) when compared with controls. Concurrent analysis of brain ABCA7 mRNA and protein revealed lower protein but not mRNA in p.L1403fs carriers, lower mRNA but not protein in p.E709fs carriers, and additional deleterious mutations in some c.5570+5G>C carriers. CONCLUSIONS: Our results suggest that LOF may not be a common mechanism for these ABCA7 variants and expand the list of neurologic diseases enriched for them.

First neuropathological description of a patient with Parkinson's disease and LRRK2 p.N1437H mutation.

The c.4309A>C mutation in the LRRK2 gene (LRRK2 p.N1437H) has recently been reported as the seventh pathogenic LRRK2 mutation causing monogenic Parkinson's disease (PD). So far, only two families worldwide have been identified with this mutation. By screening DNA from seven brains of PD patients, we found one individual with seemingly sporadic PD and LRRK2 p.N1437H mutation. Clinically, the patient had levodopa-responsive PD with tremor, and developed severe motor fluctuations during a disease duration of 19 years. There was severe and painful ON-dystonia, and severe depression with suicidal thoughts during OFF. In the advanced stage, cognition was slow during motor OFF, but there was no noticeable cognitive decline. There were no signs of autonomic nervous system dysfunction. Bilateral deep brain stimulation of the subthalamic nucleus had unsatisfactory results on motor symptoms. The patient committed suicide. Neuropathological examination revealed marked cell loss and moderate alpha-synuclein positive Lewy body pathology in the brainstem. There was sparse Lewy pathology in the cortex. A striking finding was very pronounced ubiquitin-positive pathology in the brainstem, temporolimbic regions and neocortex. Ubiquitin positivity was most pronounced in the white matter, and was out of proportion to the comparatively weaker alpha-synuclein immunoreactivity. Immunostaining for tau was mildly positive, revealing non-specific changes, but staining for TDP-43 and FUS was entirely negative. The distribution and shape of ubiquitin-positive lesions in this patient differed from the few previously described patients with LRRK2 mutations and ubiquitin pathology, and the ubiquitinated protein substrate remains undefined.

Dopamine transporter genetic variants and pesticides in Parkinson's disease.

BACKGROUND: Research suggests that independent and joint effects of genetic variability in the dopamine transporter (DAT) locus and pesticides may influence Parkinson's disease (PD) risk. METHODS: In 324 incident PD patients and 334 population controls from our rural California case-control study, we genotyped rs2652510, rs2550956 (for the DAT 5' clades), and the 3' variable number of tandem repeats (VNTR). Using geographic information system methods, we determined residential exposure to agricultural maneb and paraquat applications. We also collected occupational pesticide use data. Employing logistic regression, we calculated odds ratios (ORs) for clade diplotypes, VNTR genotype, and number of susceptibility (A clade and 9-repeat) alleles and assessed susceptibility allele-pesticide interactions. RESULTS: PD risk was increased separately in DAT A clade diplotype carriers [AA vs. BB: OR = 1.66; 95% confidence interval (CI), 1.08-2.57] and 3' VNTR 9/9 carriers (9/9 vs. 10/10: OR = 1.8; 95% CI, 0.96-3.57), and our data suggest a gene dosing effect. Importantly, high exposure to paraquat and maneb in carriers of one susceptibility allele increased PD risk 3-fold (OR = 2.99; 95% CI, 0.88-10.2), and in carriers of two or more alleles more than 4-fold (OR = 4.53; 95% CI, 1.70-12.1). We obtained similar results for occupational pesticide measures. DISCUSSION: Using two independent pesticide measures, we a) replicated previously reported gene-environment interactions between DAT genetic variants and occupational pesticide exposure in men and b) overcame previous limitations of nonspecific pesticide measures and potential recall bias by employing state records and computer models to estimate residential pesticide exposure. CONCLUSION: Our results suggest that DAT genetic variability and pesticide exposure interact to increase PD risk.

Genotype-phenotype correlates in Taiwanese patients with early-onset recessive Parkinsonism.

We screened for mutations in the PARKIN, DJ-1, and PINK1 genes in a Taiwanese cohort (68 probands; 58 sporadic and 10 familial) with early-onset parkinsonism (EOP, onset <50 years of age). We identified 9 patients harboring mutations in PARKIN (three compound heterozygous and six single heterozygous carriers), 3 patients with heterozygous PINK1 mutations (including two novel substitutions M341I and P209A), and no DJ-1 mutations. Our frequencies of PARKIN (two allele mutation, 4.4%; single allele, 8.8%) and PINK1 (single heterozygous, 4.4%) mutations in Taiwanese-Chinese are similar to those in Caucasian and other Asian EOP patients. Although the role of heterozygosity of recessive genes in EOP remains to be resolved, molecular analysis and functional imaging will play a decisive role in differential diagnosis and determined therapeutic strategy.

ATP13A2 variability in Parkinson disease.

Recessively inherited mutations in ATP13A2 result in Kufor-Rakeb syndrome (KRS), whereas genetic variability and elevated ATP13A2 expression have been implicated in Parkinson disease (PD). Given this background, ATP13A2 was comprehensively assessed to support or refute its contribution to PD. Sequencing of ATP13A2 exons and intron-exon boundaries was performed in 89 probands with familial parkinsonism from Tunisia. The segregation of mutations with parkinsonism was subsequently assessed within pedigrees. The frequency of genetic variants and evidence for association was also examined in 240 patients with nonfamilial PD and 372 healthy controls. ATP13A2 mRNA expression was also quantified in brain tissues from 38 patients with nonfamilial PD and 38 healthy subjects from the United States. Sequencing analysis revealed 37 new variants; seven missense, six silent, and 24 that were noncoding. However, no single ATP13A2 mutation segregated with familial parkinsonism in either a dominant or recessive manner. Four markers showed marginal association with nonfamilial PD, prior to correction for multiple testing. ATP13A2 mRNA expression was marginally decreased in PD brains compared with tissue from control subjects. In conclusion, neither ATP13A2 genetic variability nor quantitative gene expression in brain appears to contribute to familial parkinsonism or nonfamilial PD.