USMLE Step 1: Biochemistry & other

V1-V4

mainly V5 & V6, possibly I & aVL

• mostly young patients
• Vasculitis of medium-sized arteries
• clinical findings
  • persistent fever
  • bilateral conjunctivitis
  • cervical lymphadenopathy
  • mucocutaneous involvement
• most serious complication = formation of coronary artery aneurysms

• may result from any case of fat soluble vit malabsorption, e. g. chronic cholestasis
• causes night blindness

• rare
• severe hypoplasia of marrow erythroid precursors
• normal myeloid & megakaryocytic elements
• associated with thymoma, lymphocytic leukemias, parvovirus B19 infection

associated with either microangiopathic hemolytic anemia or mechanical red cell destruction, e. g. mechanical heart valves

associated with either microangiopathic hemolytic anemia or mechanical red cell destruction, e. g. mechanical heart valves

• young children
• clinical findings
  • acute renal failure
  • microangiopathic hemolytic anemia
  • thrombocytopenia
• laboratory
  • decreased
    • RBC count
    • hematocrit
    • platelet count
  • increased
    • bleeding time
    • LDH
    • BUN (blood urea nitrogen)
    • creatinine

abdominal aorta > coronary arteries > popliteal arteries > internal carotid arteries > circle of Willis

Age

• 95% of the children recover
• only 60% of the adults recover

• one of the most common congenital long-QT syndromes
• autosomal recessive
• associated with bilateral, severe sensorineural hearing loss

• splenic flexure & distal sigmoid colon
• are the most susceptible to ischemic damage during hypotension / low perfusion states

• slowly growing
• psammoma bodies
• mostly found in adults

• inherited inability to synthesize apolipoprotein B
• rare, autosomal recessive
• symptoms:
  • steatorrhoe
  • failure to thrive
  • intellectual disability
  • muscle weakness
  • slurred speech
  • scoliosis

Mutation of K-ras

Clomiphene = estrogen receptor modulator

• Results from a defect in the renal proximal tubules –> decreased resorption of the amio acid cystine
• clinical manifestation
  • recurrent stone formation from a young age
• Urinalysis –> pathognomonic hexagonal cystine crystals
• Diagnostic: sodium cyanide-nitroprusside test –> detects cystine's sulfhydryl groups

Failure of the paramesonephric ducts to fuse to form the uterine tubes, uterus, cervix & superior 1/3 of the vagina

failure of migration

• caused by oligohydramnios
  • bilateral agenesis of the fetal kidneys = most common cause
• affected fetuses:
  • pulmonary hypoplasia
  • limb deformitites
  • characteristic facies

• typically related to either decreased fetal swallowing or increased fetal urination
• fetal anomalies associated with impaired swallowing:
  • Gi obstruction due to duodenal, esophageal or intestinal atresia
  • anencephaly

can be caused by abnormal migration of neural crest cells through the primituve truncus arteriosus & bulbus cordis

1-4

Thymus

• inability to pass meconium
• mostly have an urogenital tract anomaly

• rare condition
• second part of the duodenum is surrounded by a ring of pancreatic tissue continuous with the head of the pancreas
• can constrict the duodenum and block or impair the flow of food
• Clinical findings: early signs of abnormality
  • polyhydramnios
  • low birth weight
  • feeding intolerance immediately after birth

• associated with poorly controlled maternal diabetes
• sacral agenesis causing lower extremity paralysis & urinary incontinence

•  occurs due to cascular accidents in utero
• if superior mesenteric artery is obstructed –> "apple-peel" atresia occurs –> manifestation: blind-ending proximal jejunum with absence of a long length of small bowel and dorsal mesentery
• terminal ileum distal to the atresia assumes a spiral configuration around an ileocolic vessel

• increased
  • anti-streptolysin O titers
  • anti-DNase B titers
• presence of cryoglobulins
• decreased C3 & total complement levels
• C4 usually normal

Neural crest cells

1. occur when the neural tube fails to fuse in the region of the ant. or post. neuropores –> persistent communication between spinal canal & amniotic cavity
2. leakage of AFP & acteylcholinesterase = prenatal diagnosis

1-6

Defect in DNA excisional repair

• painless hematuria following an upper respiratory tract infection 2-3 days ago
• when accompanied by extrarenal symptoms –> Henoch-Schönlein-Purpura