Educational objective: Neisseria meningitidis can cause sepsis and circulatory collapse in previously healthy young individuals. Lipooligosaccharide, a virulence factor in the pathogens outer membrane, is the major underlying cause of disease severity.

A 45-year-old man comes to the office for follow-up. He was diagnosed with focal epilepsy 2 years ago and has been treated with several antiepileptic medications. Over the last 6 months, his seizure frequency has increased despite compliance with medical therapy. Neurologic examination and brain imaging are unremarkable. The patient is started on a new antiepileptic medication that selectively blocks voltagegated calcium channels.

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Educational objective: Voltage-gated sodium channels are important for the generation and propagation of action potentials. When the action potential reaches the axon terminal, voltage-gated calcium channels open and allow the influx of calcium, which is essential for the fusion and release of neurotransmitter vesicles into the synaptic cleft.

A 38-year-old woman is brought to the emergency department after a motor vehicle collision. She sustained no injuries in the collision but is adamant that she did not see the car that hit her along the front side of her vehicle. The patient also reports that she has been having daily headaches and has not menstruated in 4 months. On physical examination, there is bitemporal hemianopsia but no other abnormalities. MRI of the brain is shown below.

Educational objective: All adult cells and tissues can be traced back to the 3 primary germ layers: ectoderm, mesoderm, and endoderm. The ectoderm gives rise to the surface ectoderm, neural tube, and neural crest.

A 16-year-old boy with mild intellectual disability is brought to the office to be evaluated for attention deficithyperactivity disorder. The parents state that he has always been impulsive and inattentive and that teachers are concerned about his inattentiveness and poor grades. Review of medical records shows a history of gross motor and speech delay for which he received physical and speech therapies during childhood. On physical examination, the boy has a long and narrow face, a prominent mandible, and large testes. There is hyperlaxity of his finger and thumb joints.

Educational objective: Fragile X syndrome is an X-linked disorder that presents with a long, narrow face, a prominent chin and forehead, and large testes. Patients often have developmental delay and neuropsychiatric findings that overlap with anxiety disorders, autism, and attention deficit-hyperactivity disorder.

A 41-year-old man with trisomy 21 is evaluated in the clinic due to cognitive decline. The patient has a history of moderate intellectual disability, but his higher cognitive functions have become progressively impaired in the past several years. He previously volunteered at a community library but recently lost his position as he could no longer perform his duties. The patient is now completely dependent on a caregiver for assistance with his activities of daily living such as getting dressed, bathing, and using the toilet. The patient keeps wandering in the group home and has become lost on several occasions.

Educational objective: Patients with trisomy 21 (Down syndrome) have 3 copies of the amyloid precursor protein gene located on chromosome 21. This increases amyloid-beta accumulation in the brain, placing these patients at high risk for developing early-onset Alzheimer disease.

A 35-year-old woman, gravida 2 para 1, comes to the office for a routine prenatal visit. Her first child was born with a hydrocele and syndactyly of the first and second toes. The patient has no significant medical problems and takes no medications except for a multivitamin. Examination reveals clear lungs and normal first and second heart sounds. The abdomen is soft and nontender. Uterine size, fetal movements, and fetal cardiac activity are all within appropriate limits. The patient undergoes amniocentesis during the 18th week of pregnancy. Amniotic fluid analysis shows an increased level of acetylcholinesterase.

Educational objective: Neural tube defects most often occur when the neural folds fail to fuse in the region of the anterior or posterior neuropores. Persistent communication between the spinal canal and the amniotic cavity allows leakage of alpha-fetoprotein (AFP) and acetylcholinesterase (AChE) into the amnionic fluid, leading to elevated levels of AFP and AChE that can be detected on amniocentesis.

A 34-year-old man comes to the hospital due to several hours of difficulty swallowing, dry mouth, and blurred vision. The patient has a history of major depression. Examination shows mydriasis and poorly reactive pupils. Electrodiagnostic studies reveal normal nerve conduction velocity but decreased compound muscle action potential (CMAP). Rapid, repetitive nerve stimulation leads to facilitation of CMAP.

Educational objective: Botulinum neurotoxin produced by C/ostridium botulinum prevents the release of acetylcholine from presynaptic nerve terminals. The toxin impairs peripheral muscarinic and nicotinic neurotransmission, causing both autonomic symptoms (eg, fixed pupillary dilation, dry mouth) and skeletal muscle weakness (eg, diplopia, dysphagia, respiratory depression).