F ragile X associated tremor/ataxia syndrome (FXTAS) is a recently identified neurodegenerative disorder affecting older adult males with pre-mutation alleles of the fragile X mental retardation 1 (FMR1) gene. [1][2][3] These male carriers, in their fifties and older, develop progressive intention tremor, cerebellar ataxia, progressive cognitive difficulties, and variable features including peripheral neuropathy, lower limb proximal muscle weakness, and autonomic dysfunction.Radiological signs include global brain atrophy and white matter disease characterised by hyperintensities in the middle cerebellar peduncles (MCP) on T2 sequence with scattered periventricular disease, corresponding to spongiform changes and demyelination on neuropathological studies. 2Here we report three pre-mutation carriers (two sisters and one sporadic case) presenting with spastic paraparesis, cerebellar ataxia, and intention tremor, and having neuroimaging features suggestive of a severe variant of FXTAS. A random X inactivation pattern was found in the two affected sisters. The third female sibling was unaffected and her inactivation pattern was significantly skewed. This suggests that the X inactivation ratio may be responsible for the incomplete penetrance of the neurological symptoms in this family. CASE DESCRIPTIONS Case 1 (II-2)The first sister developed spasticity and balance difficulty in the third decade of her life. During this time, she underwent neurological evaluation. She was well oriented, with intact speech and cognitive function. Examination of the lower extremity showed paraparesis, mild spasticity, and positive Babinski. The upper extremities showed diminished coordination and intention tremor. EEG, ECG fundoscopy, electromyography (EMG), and nerve conduction studies were normal. Cerebrospinal fluid (CSF) was normal, with absence of oligoclonal bands. Muscle biopsy showed a chronic neurogenic process. She had anxiety and mild depression. Case 2 (II-3)The other sister gradually developed spasticity with dragging of the toes while walking, lower limb weakness, and difficulty with balance. Neurological evaluation at 35 years of age showed normal cognitive functions. Examination of the lower extremities, showed paraparesis, mild spasticity, positive Babinski, extensor plantar responses, mild muscle wasting, pes cavus, hammer toes, acrocyanosis, and loss of proprioception and vibratory sensation from the knees downwards. Gait was wide based and uncoordinated, with hyperextension of the knees. The upper extremities had mild incoordination and intention tremor. EEG, ECG, fundoscopy EMG, and nerve conduction studies were normal. CSF was normal, with no oligoclonal bands. Motor evoked potentials showed abnormal central motor conduction especially in the right limb. Muscle biopsy was abnormal, demonstrating a mild neurogenic process. Spasticity increased, requiring the use of a walker and, subsequently a wheelchair. She was found to be anxious and presented a mild hearing loss. Both sisters (case 1 and case 2) had been clini...
Human beings are predisposed to think of evolution as teleological-i.e., having a purpose or directive principle-and the ways scientists talk about natural selection can feed this predisposition. This work examines the suggestion that students' teleological thinking operates as an obstacle when the natural selection evolution model is taught. What we mean by obstacle is an established way of thinking that resists change due to its explanatory power. In light of this approach, the challenges of teaching evolution in biology education have been revised, and improved methodological strategies aimed at a better comprehension of the Darwinian evolution model are suggested.
Background Teleology is one of the critical aspects of students’ intuitive concepts about living beings and, specifically, their evolution. This cognitive bias imposes a substantial restriction on the process of learning such content. In this work, we rely on epistemological, psychological and pedagogical analyses to substantiate an educational proposal centered on the concepts of epistemological obstacles and metacognitive vigilance. Results Based on Michael Ruse’s epistemological analysis, according to which teleology in biology persists because the scientific explanation of adaptation necessarily involves appeal to the metaphor of design, and on research in cognitive psychology, especially in relation to metacognition and self-regulated learning, we argue that the primary educational aim must be to encourage students to develop metacognitive skills to regulate the use of teleological reasoning. We develop our instructional proposal based on the didactic concepts of epistemological obstacles and metacognitive vigilance (consistent with epistemological and psychological analyses). Conclusion We briefly discuss the instructional implications of our analysis and some possible relationships between our proposal and other lines of research in psychology and science education.
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