Cell & Cytoskeleton Diseases
A child presents with recurrent infections, eczema, and thrombocytopenia. Genetic testing reveals an X-linked mutation affecting a protein involved in activation of the Arp2/3 complex.
Answer: Wiskott-Aldrich syndrome
A newborn develops a diffuse scalp swelling after a prolonged labor. The swelling crosses cranial sutures and does not cause significant systemic instability.
Answer: Caput succedaneum
A 70-year-old postmenopausal woman suffers a hip fracture after a minor fall. Bone biopsy demonstrates thin, perforated trabeculae with normal mineralization.
Answer: Osteoporosis
A young boy develops progressive proximal muscle weakness, difficulty climbing stairs, and muscle fiber degeneration. Biopsy shows variable fiber size, fibrosis, and fatty replacement.
Answer: Duchenne muscular dystrophy
A patient develops flaccid paralysis after eating improperly canned food. The responsible toxin prevents neurotransmitter release from presynaptic terminals.
Answer: Botulism
A patient presents with anemia, jaundice, and splenomegaly. Peripheral smear demonstrates spherical RBCs with loss of the normal biconcave shape.
Question: Which cytoskeletal defect is most likely responsible?
Answer: Hereditary spherocytosis
A newborn develops a scalp swelling confined to one cranial bone because it is limited by the sutures. The infant is otherwise stable.
Answer: Cephalohematoma
A child presents with bone pain and skeletal deformities due to inadequate mineralization of newly formed bone.
Answer: Rickets
A patient develops fatigable skeletal muscle weakness that worsens with repeated use. Autoantibodies target nicotinic acetylcholine receptors.
Answer: Myasthenia gravis
A farmer develops salivation, lacrimation, diarrhea, muscle fasciculations, and respiratory weakness after pesticide exposure.
Answer: Organophosphate poisoning
A patient with hereditary spherocytosis undergoes splenectomy, after which hemolysis decreases substantially.
Question: Why does this treatment reduce hemolysis?
Answer: The spleen is the major site of extravascular destruction of the abnormal, rigid spherocytes.
A newborn following vacuum extraction develops a boggy scalp swelling that crosses sutures and rapidly becomes pale and tachycardic.
Question: What makes this condition potentially fatal?
Answer: Subgaleal hemorrhage, because blood can spread throughout the loose areolar space and produce massive blood loss.
A patient develops increased bone turnover due to excessive parathyroid hormone activity.
Question: What is the direct effect of PTH on osteoclasts?
Answer: PTH indirectly stimulates osteoclasts by increasing RANKL signaling from osteoblast-lineage cells.
A young athlete experiences sudden cardiac death. Cardiac muscle demonstrates hypertrophy, myofibrillar disarray, and interstitial fibrosis.
Answer: Hypertrophic cardiomyopathy
A patient develops severe muscle rigidity and painful spasms after a contaminated wound.
Question: Why does this toxin produce spastic rather than flaccid paralysis?
Answer: Tetanus toxin blocks GABA and glycine release from inhibitory interneurons, causing loss of motor neuron inhibition.
A patient with hereditary spherocytosis has a mutation in a protein that normally links the spectrin-actin cytoskeleton to the RBC membrane.
Question: Which protein is most likely affected?
Answer: Ankyrin
A 52-year-old patient develops flaccid bullae and painful oral erosions. Biopsy shows acantholysis and an intraepidermal blister.
Question: Which adhesion molecule is targeted?
Answer: Pemphigus vulgaris → desmoglein-3
A child has recurrent fractures, anemia, hepatosplenomegaly, and cranial nerve palsies. Imaging demonstrates diffusely dense bones and obliterated marrow cavities.
Answer: Osteopetrosis
A woman has an enlarging uterine mass. Histology demonstrates whorled bundles of bland spindle-shaped smooth muscle cells with rare mitoses.
Answer: Leiomyoma
A neonate has abdominal distension, bilious vomiting, failure to pass meconium, and absence of ganglion cells in the myenteric and submucosal plexuses.
Answer: Hirschsprung disease
A patient develops progressive muscle weakness due to a defect in the protein that mechanically links the sarcomere to the extracellular matrix. Repeated contractions cause membrane injury and Ca²⁺ influx.
Question: Which disease is characterized by this mechanism?
Answer: Duchenne muscular dystrophy
A patient develops tense, subepidermal bullae due to autoantibodies against proteins anchoring basal keratinocytes to the basement membrane.
Question: Which disease is most likely, and what type of junction is affected?
Answer: Bullous pemphigoid → hemidesmosomes
A patient has chronic joint pain with progressive loss of articular cartilage.
Question: Which disease is characterized by degeneration of the cartilage covering synovial joint surfaces?
Answer: Osteoarthritis
A 25-year-old patient develops episodes of muscle weakness and paralysis after prolonged rest following strenuous exercise. The episodes are associated with abnormal skeletal muscle excitability and are triggered by changes in serum potassium concentration. The underlying disorder involves an abnormality of the skeletal muscle ion channels responsible for maintaining the resting membrane potential.
What is the most likely condition?
Answer: Hypokalemic periodic paralysis
A newborn has congenital sensorineural deafness, abnormal pigmentation, and heterochromia.
Question: Which neural crest-derived cell type is primarily responsible for the pigmentation abnormality?
Answer: Waardenburg syndrome → melanocytes