<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 46-year-old woman comes to the physician for a cognitive evaluation. She is an office manager. She has had increasing difficulties with multitasking and reports that her job performance has declined over the past 1 year. On mental status examination, short-term memory is impaired and long-term memory is intact. Laboratory studies, including thyroid-stimulating hormone and vitamin B12, are within the reference range. An MRI of the brain shows generalized atrophy, most pronounced in the bilateral medial temporal lobes and hippocampi. If this patients condition has a genetic etiology, which of the following alterations is most likely to be found on genetic testing?? A: Noncoding hexanucleotide repeats, B: Deletion of chromosome 21q, C: Mutation in presenilin 1, D: Expansion of CAG trinucleotide repeat, E: Presence of ApoE ε4 allele,  <response>: This is a question about genetic causes of cognitive impairment and brain atrophy, particularly affecting the medial temporal lobes and hippocampi. The description of impaired short-term memory with relatively intact long-term memory points towards a diagnosis of early Alzheimers disease. The imaging findings of medial temporal lobehippocampal atrophy also support this diagnosis. The key genetic causes of early-onset Alzheimers disease involve mutations in one of three genes: amyloid precursor protein APP, presenilin 1 PSEN1, or presenilin 2 PSEN2. Mutations in these genes lead to abnormal aggregation of amyloid beta in the brain, which is believed to drive the pathogenesis of Alzheimers. Of the answer choices provided, a mutation in the presenilin 1 gene is most likely to be found in genetic testing of a patient with early-onset Alzheimers disease presenting with the provided history and examination findings.C: Mutation in presenilin 1 