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Neurologic system
Broca aphasia
Wernicke aphasia
Kluver-Bucy syndrome
Acoustic neuroma (schwannoma)
Adult brain tumors
Pediatric brain tumors
Pituitary adenoma
Adult brain tumors: Pathology review
Pediatric brain tumors: Pathology review
Brain herniation
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Cerebral vascular disease: Pathology review
Aqueductal stenosis
Cerebral palsy
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Spina bifida
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Tethered spinal cord syndrome
Congenital neurological disorders: Pathology review
Alzheimer disease
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Frontotemporal dementia
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Normal pressure hydrocephalus
Vascular dementia
Dementia: Pathology review
Acute disseminated encephalomyelitis
Central pontine myelinolysis
JC virus (Progressive multifocal leukoencephalopathy)
Multiple sclerosis
Transverse myelitis
Demyelinating disorders: Pathology review
Cavernous sinus thrombosis
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Migraine
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Trigeminal neuralgia
Headaches: Pathology review
Brain abscess
Cavernous sinus thrombosis
Creutzfeldt-Jakob disease
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Central nervous system infections: Pathology review
Arteriovenous malformation
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Adrenoleukodystrophy (NORD)
Leukodystrophy
Essential tremor
Huntington disease
Opsoclonus myoclonus syndrome (NORD)
Parkinson disease
Restless legs syndrome
Torticollis
Movement disorders: Pathology review
Wernicke-Korsakoff syndrome
Zellweger spectrum disorders (NORD)
Peroxisomal disorders: Pathology review
Early infantile epileptic encephalopathy (NORD)
Epilepsy
Febrile seizure
Seizures: Pathology review
Brown-Sequard Syndrome
Cauda equina syndrome
Friedreich ataxia
Neurogenic bladder
Syringomyelia
Treponema pallidum (Syphilis)
Vitamin B12 deficiency
Spinal cord disorders: Pathology review
Concussion and traumatic brain injury
Shaken baby syndrome
Traumatic brain injury: Pathology review
Amyotrophic lateral sclerosis
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Sturge-Weber syndrome
Tuberous sclerosis
von Hippel-Lindau disease
Neurocutaneous disorders: Pathology review
Horner syndrome
Orthostatic hypotension
Charcot-Marie-Tooth disease
Guillain-Barre syndrome
Bell palsy
Trigeminal neuralgia
Poliovirus
Spinal muscular atrophy
Lambert-Eaton myasthenic syndrome
Myasthenia gravis
Neuromuscular junction disorders: Pathology review
Carpal tunnel syndrome
Erb-Duchenne palsy
Klumpke paralysis
Sciatica
Thoracic outlet syndrome
Ulnar claw
Winged scapula
Huntington disease
0 / 16 complete
0 / 5 complete
of complete
of complete
2022
2021
2020
2019
2018
2017
2016
Huntington disease p. 538
Huntington disease p. 538
Huntington disease p. 538
Huntington disease p. 538
Huntington disease p. 538
basal ganglia lesions p. 528
neurodegenerative disorder p. 538
neurotransmitters for p. 512
ventromegaly p. 540
Huntington disease, or HD, is a rare neurodegenerative disease that involves a repeated sequence of DNA that causes an abnormal protein to form, leading to abnormal movements and cognitive problems.
Huntington disease is an autosomal dominant genetic disorder, which means that one affected copy of a gene is enough to cause disease. Affected people are typically present in each generation, because an affected person (male or female) has a 50% chance of passing on the affected gene to a child, which causes that child to have the disease.
In most people, a gene called huntingtin or HTT on chromosome 4, contains a triplet repeat, where the nucleotides C, A, and G are repeated 10-35 times in a row. In people with Huntington disease, this repeat goes on for 36 or more times in a row. CAG codes for the amino acid glutamine, so people with Huntington disease patients will have 36 or more glutamines in a row in the huntingtin protein. So, in addition to being a triplet repeat disorder, HD is, more specifically, a “polyglutamine” disease.
The specific way in which extra glutamines cause HD symptoms isn’t fully worked out, but some clues are that the mutated protein aggregates within the neuronal cells of the caudate and putamen of the basal ganglia causing neuronal cell death. Cell death might be related to excitotoxicity – which is excessive signaling of these neurons, which leads to high intracellular calcium.
The expanded CAG repeats not only affect the huntingtin protein – they affect DNA replication itself. When copying the HTT gene, DNA polymerase can basically lose track of which CAG it’s on and accidently add extra CAGs. Since as a zygote develops into a fetus and eventually into a full adult, by the time sperm and eggs are created, several dozen cell divisions, each with a round of DNA replication have taken place, and so there have already been ample opportunities for repeat expansion, and the more repeats that’re added, the more unstable it gets.
This expansion of the originally inherited gene means a child of a parent with HD can inherit even more CAG repeats than the parent did. The higher the number of repeats in the protein, the earlier the age when a person starts having symptoms. This phenomenon is called anticipation, which means that Huntington disease families often show earlier symptom onset with each generation. Even repeats of 27-35 CAGs can expand occasionally; these are called “pre-mutation” alleles, since they don’t cause the disease, but they’re set-up for developing a mutation of 36 or more CAGs.
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