Complex Genetic Disease: Can Genetic Strategies in Alzheimer's Disease and New Genetic Mechanisms Be Applied to Epilepsy?

Summary: Strategies used in molecular genetics have changed modern neurology. The gene or genes responsible for several major neurologic diseases have now been identified using "reverse" or positional genetics. Unexpected new genetic mechanisms have been discovered in human neurologic diseases, including (a) identical mutations of the prion protein gene in Creutzfeldt-Jakob disease and fatal familial insomnia with the phenotypic expression directed by an accompanying polymorphism; (b) stable duplications of chromosome 17 in Charcot-Marie-Tooth disease (type 1 A) that involve many genes, only one of which appears to cause neuropathy; and (c) highly variable, dynamic mutations in myotonic dystrophy, fragile X syndrome, and Kennedy's syndrome that modulate variable expressivity in multiple tissues. There is growing recognition that neurologic diseases are often complex genetic diseases with multifactorial rather than simple modes of inheritance. For example, genetic association/linkage strategies have interacted with biochemistry and immunopathology studies to produce new insights into the disease mechanism of late-onset Alzheimer's disease. The role of apolipoprotein E in late-onset Alzheimer's disease is an example of how new analytical techniques of genetic disease can be applied to dissect multiple genes. Similar research strategies are suggested for the study of epilepsy as a complex disease.     

Neurodegeneration in the Central Nervous System of apoE-Deficient Mice

Apolipoprotein E (apoE) is involved in the development and regeneration of the central nervous system (CNS). ApoE may also be necessary to maintain the integrity of the synapto-dendritic complexity. We analyzed the synaptic alterations in the CNS of apoE-deficient (knockout) mice during the aging process. In apoE-deficient homozygous mice, there was an age-dependent 15 to 40% loss of synaptophysin-immunoreactive nerve terminals and microtubule-associated protein 2-immunoreactive dendrites in the neocortex and hippocampus, when compared to controls. Dendritic alterations were observed as early as 4 months of age. Ultrastructural analysis revealed extensive dendritic vacuolization and disruption of the endomembrane system and cytoskeleton in apoE-deficient homozygous mice. Further immunocytochemical studies of the neuronal cytoskeleton showed that in apoE-deficient mice there was a decrease in the immunoreactivity of α and β tubulin (but not kinesin) in the cell bodies and processes. These results support the contention that apoE might play an important role in maintaining the stability of the synapto-dendritic apparatus and that altered or deficient functioning of this molecule could underlie the synaptic and cytoskeletal alterations in Alzheimer's disease.     

Complete genomic screen in Parkinson disease: evidence for multiple genes.

CONTEXT: The relative contribution of genes vs environment in idiopathic Parkinson disease (PD) is controversial. Although genetic studies have identified 2 genes in which mutations cause rare single-gene variants of PD and observational studies have suggested a genetic component, twin studies have suggested that little genetic contribution exists in the common forms of PD. OBJECTIVE: To identify genetic risk factors for idiopathic PD. DESIGN, SETTING, AND PARTICIPANTS: Genetic linkage study conducted 1995-2000 in which a complete genomic screen (n = 344 markers) was performed in 174 families with multiple individuals diagnosed as having idiopathic PD, identified through probands in 13 clinic populations in the continental United States and Australia. A total of 870 family members were studied: 378 diagnosed as having PD, 379 unaffected by PD, and 113 with unclear status. MAIN OUTCOME MEASURES: Logarithm of odds (lod) scores generated from parametric and nonparametric genetic linkage analysis. RESULTS: Two-point parametric maximum parametric lod score (MLOD) and multipoint nonparametric lod score (LOD) linkage analysis detected significant evidence for linkage to 5 distinct chromosomal regions: chromosome 6 in the parkin gene (MLOD = 5.07; LOD = 5.47) in families with at least 1 individual with PD onset at younger than 40 years, chromosomes 17q (MLOD = 2.28; LOD = 2.62), 8p (MLOD = 2.01; LOD = 2.22), and 5q (MLOD = 2.39; LOD = 1.50) overall and in families with late-onset PD, and chromosome 9q (MLOD = 1.52; LOD = 2.59) in families with both levodopa-responsive and levodopa-nonresponsive patients. CONCLUSIONS: Our data suggest that the parkin gene is important in early-onset PD and that multiple genetic factors may be important in the development of idiopathic late-onset PD.     

Association of single-nucleotide polymorphisms of the tau gene with late-onset Parkinson disease.

CONTEXT: The human tau gene, which promotes assembly of neuronal microtubules, has been associated with several rare neurologic diseases that clinically include parkinsonian features. We recently observed linkage in idiopathic Parkinson disease (PD) to a region on chromosome 17q21 that contains the tau gene. These factors make tau a good candidate for investigation as a susceptibility gene for idiopathic PD, the most common form of the disease. OBJECTIVE: To investigate whether the tau gene is involved in idiopathic PD. DESIGN, SETTING, AND PARTICIPANTS: Among a sample of 1056 individuals from 235 families selected from 13 clinical centers in the United States and Australia and from a family ascertainment core center, we tested 5 single-nucleotide polymorphisms (SNPs) within the tau gene for association with PD, using family-based tests of association. Both affected (n = 426) and unaffected (n = 579) family members were included; 51 individuals had unclear PD status. Analyses were conducted to test individual SNPs and SNP haplotypes within the tau gene. MAIN OUTCOME MEASURE: Family-based tests of association, calculated using asymptotic distributions. RESULTS: Analysis of association between the SNPs and PD yielded significant evidence of association for 3 of the 5 SNPs tested: SNP 3, P =.03; SNP 9i, P =.04; and SNP 11, P =.04. The 2 other SNPs did not show evidence of significant association (SNP 9ii, P =.11, and SNP 9iii, P =.87). Strong evidence of association was found with haplotype analysis, with a positive association with one haplotype (P =.009) and a negative association with another haplotype (P =.007). Substantial linkage disequilibrium (P<.001) was detected between 4 of the 5 SNPs (SNPs 3, 9i, 9ii, and 11). CONCLUSIONS: This integrated approach of genetic linkage and positional association analyses implicates tau as a susceptibility gene for idiopathic PD.     

Do microscopic surgical margins matter for primary gastric gastrointestinal stromal tumor?

BackgroundAlthough tumor size and mitotic rate are established prognostic factors for worse survival in patients undergoing surgical resection for gastric gastrointestinal stromal tumors, the impact of microscopic margins, or R1 resection, is not completely established.MethodsPatients who received no neoadjuvant therapy and underwent surgical resection for stage I to III gastric gastrointestinal stromal tumors were identified from the 2010 to 2013 National Cancer Database and divided into 2 cohorts, R0 and R1 resections. Cox proportional hazards ratio and Kaplan Meier survival estimates were utilized to analyze 5-y overall survival.ResultsOf 2,084 patients, those with R1 resection (57, 2.7%) were more likely to have tumors >10 cm (28.1% vs 11.9%, odds ratio 3.51, P = .017) and stage III disease (26.3% vs 11.2%, odds ratio 2.26, P = .047). Although margin status was associated with higher risk tumors, it was not associated with receipt of adjuvant therapy. After multivariate Cox regression, R1 and R0 patients did not have a difference in 5-y overall survival (82.5% vs 88.6%, hazards ratio 1.26, P = .49). When stratified by stage of disease, there remained no difference in survival across all stages when comparing R1 and R0 patients.ConclusionPositive microscopic margins are uncommon but do not appear to impact survival outcomes in patients with resected localized gastric gastrointestinal stromal tumors.     

Sialylated human apolipoprotein E (apoEs) is preferentially associated with neuron-enriched cultures from APOE transgenic mice

Mice transgenic for human APOE2, E3, and E4 alleles express native 34-kDa human apoE and two sialylated apoE isoproteins with approximate molecular weights of 37 kDa (apoEs) and 39 kDa (apoEs2) in brain. These multiple apoE/apoEs/apoEs2 band patterns on Western blot are also observed in human brain, but are not seen in wild-type mouse brain. Both the 37-kDa apoEs and 39-kDa apoEs2 are coprecipitated with native 34-kDa apoE by antibody to human apoE. Neuraminidase digestion eliminates the 37- and 39-kDa forms and results in a downward shift in the bands to the position of the 34-kDa native form. These sialylated apoE isoproteins are found preferentially associated with neurons and contribute significantly (50-60%) to the total neuronal apoE in neuronal cultures from transgenic mice, while only 5-10% of total apoE is sialylated in cultures enriched in glial cells. In situ hybridization and immunocytochemistry demonstrate apoE mRNA and apoE immunoreactivity are predominantly located in cell soma of neurons, not in neuronal processes.     

Increased neuronal damage in apolipoprotein E-deficient mice following global ischaemia

There is accumulating evidence that apolipoprotein E (apoE) plays a role in regulating the response to and outcome following brain injury. The present study compared the histological outcome and recovery following an episode of global ischaemia in apoE-deficient mice and wild-type littermates (12-week-old males, n = 8 per group). Transient global ischaemia was induced for a period of 17 min and the animals were allowed to recover for 72 h. Transient global ischaemia induced selective neuronal degeneration in several brain regions in wild-type mice. There was statistically significant increased ischaemic neuronal damage in apoE-deficient mice compared with wild-type mice in six of the seven regions examined (hippocampal regions CA1, CA3/CA4 and dentate gyrus; thalamus; cortex and caudate nucleus; P < 0.05). The data substantiate a role for apoE in modifying the response of the CNS to acute injury.     

Evaluation and detection of Duchenne's and Becker's muscular dystrophy carriers by manual muscle testing

Manual muscle testing of mothers of patients with X-linked muscular dystrophy has demonstrated patterns of proximal muscle weakness. The degree of weakness usually has little effect on activities of daily living but can be detected by standardized "break" testing with manual stabilization of body parts, elimination of synergistic muscles, and mechanical advantage given to the patient. Manual muscle testing is a valuable adjunct to the clinical and biochemical tools available for detecting carriers.