Clinical, neuropathological and genotypic variability in SNCA A53T familial Parkinson's disease. Variability in familial Parkinson's disease.

Individuals with familial Parkinson's disease (PD) due to a monogenic defect can show considerable clinical and neuropathological variability. To identify factors underlying this variability, histopathological analysis was performed in two clinically different A53T alpha-synuclein heterozygotes from Family H, a multigenerational alpha-synuclein A53T kindred. To determine whether additional genetic factors could contribute to phenotypic variability, Family H and another multigenerational A53T kindred were analyzed for parkin polymorphisms. We identified a previously described variant in parkin exon 4 associated with increased PD risk (S167N). The two A53T heterozygotes had markedly different neuropathology and different parkin genotypes: A N167 homozygote had early onset rapidly progressive disease, early dementia, myoclonus and sleep disorder, while a S167 homozygote had late onset, slowly progressive disease and late dementia. Both had brainstem, cortical, and intraneuritic Lewy bodies (LB). The N167 individual had widespread cortical neurofibrillary degeneration, while the S167 individual had only medial temporal lobe neurofibrillary degeneration. The N167 individual had severe neuronal loss in CA2 associated with Lewy neurites (LN), while the S167 individual had severe neuronal loss in CA1 associated with TDP-43 immunoreactive neuronal inclusions. These findings implicate TDP-43 in the pathology of familial PD and suggest that parkin may act as a modifier of the A53T alpha-synuclein phenotype of familial PD. Furthermore, they suggest a mechanism by which a rare genetic variant that is associated with a minor increase of PD risk in the heterozygous state may, in the homozygous state, exacerbate a disease phenotype associated with a highly penetrant dominant allele.

Reduced expression of the G209A alpha-synuclein allele in familial Parkinsonism.

Missense mutations at the alpha-synuclein gene have been associated with familial parkinsonism. We report that the phenotype of a kindred (Family H) with autosomal dominant, levodopa-responsive parkinsonism maps to chromosomal region 4q21-23 and that affected members of this kindred harbor a previously reported mutation (G209A) in exon 4 of the alpha-synuclein gene. We assessed the expression of the G209A allele in lymphoblastoid cell lines established from 12 individuals heterozygous for the G209A allele. The expression of this allele is either absent or significantly reduced in 7 affected heterozygotes and in 3 asymptomatic heterozygotes who are older than the mean age at disease diagnosis for their generation. In contrast, it is expressed in 1 affected and 1 unaffected heterozygote. The unaffected heterozygote is younger than the mean age at disease diagnosis for their generation. The lack of or significantly reduced expression of the G209A allele in affected heterozygotes suggests that the timing of reduced expression may be critical for disease onset. If so, the parkinsonian phenotype may arise from haploinsufficiency at the alpha-synuclein gene at a time point before symptom onset. In conclusion, reduced alpha-synuclein gene expression may be important in the pathogenesis of parkinsonism.

A genetic analysis of intersex, a gene regulating sexual differentiation in Drosophila melanogaster females.

Sex-type in Drosophila melanogaster is controlled by a hierarchically acting set of regulatory genes. At the terminus of this hierarchy lie those regulatory genes responsible for implementing sexual differentiation: genes that control the activity of target loci whose products give rise to sexually dimorphic phenotypes. The genetic analysis of the intersex (ix) gene presented here demonstrates that ix is such a terminally positioned regulatory locus. The ix locus has been localized to the cytogenetic interval between 47E3-6 and 47F11-18. A comparison of the morphological and behavioral phenotypes of homozygotes and hemizygotes for three point mutations at ix indicates that the null phenotype of ix is to transform diplo-X animals into intersexes while leaving haplo-X animals unaffected. Analysis of X-ray induced, mitotic recombination clones lacking ix+ function in the abdomen of diplo-X individuals indicates that the ix+ product functions in a cell-autonomous manner and that it is required at least until the termination of cell division in this tissue. Taken together with previous analyses, our results indicate that the ix+ product is required to function with the female-specific product of doublesex to implement appropriate female sexual differentiation in diplo-X animals.

On the role of normal acetylcholine metabolism in the formation and maintenance of the Drosophila nervous system.

We have examined the requirement for normal acetylcholine metabolism in the formation and maintenance of the larval and adult central nervous system in Drosophila melanogaster. By using mutations at the Ace and Cha loci, which respectively encode the degradative and synthetic enzymes for acetylcholine (ACh), acetylcholinesterase (AChE), and choline acetyltransferase (ChAT), we have been able to disrupt acetylcholine metabolism in situ. An ultrastructural analysis of embryonic nervous tissue lacking either enzymatic function has indicated that while neither function is required for the formation of the larval central nervous system, each is required for the subsequent maintenance of its structural integrity and function. Using temperature sensitive mutations at the Cha locus, the normal developmental profile of ChAT activity during the late larval and pupal stages was disrupted. Subsequent examination of the morphology and behavior of the treated animals has indicated that normal acetylcholine metabolism is not required for the initial formation of the adult nervous system, but is required for the subsequent maintenance of its structural integrity and function. The results obtained in these studies are discussed with respect to data presented on the adult distribution of the cholinergic markers' AChE activity and ChAT immunoreactivity. The projections of adult peripheral neurons innervating Ace+ tissue from Ace cuticular clones has been examined to address the nature of the structure of Ace neuropil. Normal projections are apparently achieved and maintained, suggesting that the defects seen in adult Ace mosaics arise as an aberrant intracellular organization of morphologically normal cells.

Monoclonal antibodies with defined specificities for Torpedo nicotinic acetylcholine receptor cross-react with Drosophila neural tissue.

A panel of monoclonal antibodies with known specificity for the well-characterized nicotinic acetylcholine receptor from the electroplax of Torpedo californica, many of which cross-react with the mammalian muscle acetylcholine receptor, were examined for cross-reactivity in the fly, Drosophila melanogaster. Monoclonal antibodies with specificities for different epitopes on the transmembrane receptor complex from Torpedo cross-react with different regional subsets of neural tissue in Drosophila. Axonal tracts, neuropil, mechano-sensory bristle elements and photoreceptors, each are detected by separate monoclonal antibody classes corresponding to different epitope domains. A preliminary characterization of an antigenic determinant in Drosophila heads recognized by one of the cross-reacting monoclonal antibodies is presented. Monoclonal antibodies such as these may be useful in identifying molecules of homologous structure or function, possibly including a neuronal acetylcholine receptor.

A genetic analysis of glutamatergic function in Drosophila.

Neurotransmitters are essential for communication between neurons and hence are vital in the overall integrative functioning of the nervous system. Previous work on acetylcholine metabolism in the fruit fly, Drosophila melanogaster, has also raised the possibility that transmitter metabolism may play a prominent role in either the achievement or maintenance of the normal structure of the central nervous system in this species. Unfortunately, acetylcholine is rather poorly characterized as a neurotransmitter in Drosophila; consequently, we have begun an analysis of the role of glutamate (probably the best characterized transmitter in this organism) in the formation and/or maintenance of nervous system structure. We present here the results of a series of preliminary analyses. To suggest where glutamatergic function may be localized, an examination of the spatial distribution of high affinity [3H]-glutamate binding sites are presented. We present the results of an analysis of the spatial and temporal distribution of enzymatic activities thought to be important in the regulation of transmitter-glutamate pools (i.e., glutamate oxaloacetic transaminase, glutaminase, and glutamate dehydrogenase). To begin to examine whether mutations in any of these functions are capable of affecting glutamatergic activity, we present the results of an initial genetic analysis of one enzymatic function, glutamate oxaloacetic transaminase (GOT), chosen because of its differential distribution within the adult central nervous system and musculature.

Abdominal pain, atherosclerosis, and atrial fibrillation. The case for mesenteric ischemia.

DT, a 63-year-old white male with insulin-dependent diabetes mellitus and severe peripheral vascular disease, was admitted with a five-day history of vague abdominal pain and diarrhea. On the day of admission he vomited three times, was noted to have a bloody stool, and came to the emergency room. DT denied hematemesis, fever, or chills. He had bilateral leg amputations and had sustained three myocardial infarctions, the last one 15 months before this admission. He had never experienced symptoms of abdominal angina. Of significance was his history of congestive heart failure, mitral regurgitation, and atrial fibrillation. His medications on admission included digoxin 0.25mg per day, furosemide 40mg per day, and NPH insulin 15 units per day. On admission to the hospital his oral temperature was 38 degrees C, pulse was 90/min, respiratory rate was 24/min, and blood pressure was 134/80mmHg. Abdominal examination revealed a distended abdomen with hypoactive bowel sounds and mild tenderness. Chest x ray revealed cardiomegaly. The electrocardiogram demonstrated atrial fibrillation. A plain film of the abdomen was positive for gallstones and edema of the bowel wall (thumb-printing). Laboratory results included blood urea nitrogen 48mg%, creatinine 1.2mg%, hemoglobin 18g/dl, and hematocrit 52.9%. White blood cell count was 11,900 cells/cc with 33% polymorphonuclear leukocytes, 47% bands, 8% lymphocytes, 11% monocytes, and 1% atypical lymphocytes. The prime considerations for differential diagnosis were mesenteric ischemia and infectious gastroenteritis. While it was appreciated that mesenteric ischemia, if present, might warrant surgical intervention, the risk of anesthesia itself in this patient was felt by his attending physicians to exceed 30%. Furthermore, the clinical findings were only "suggestive" of mesenteric eschemia. They were certainly not "diagnostic." In view of this dilemma, a consultation with the Division of Clinical Decision Making was requested.