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2013 First Aid for the USMLE Step 1
Official Updates, Corrections, and Clarifications
Last Revised: May 13th, 2013
Despite our best efforts, errors do occur during a revision. This update addresses content errors and typos that may create confusion. If you are the first to submit a referenced correction or suggestion to us at www.firstaidteam.com that we accept and integrate into the book, you will receive up to a $20 gift certificate. We check every submission against your reference or other authoritative references to ensure accuracy. Please note that our goal is to provide a high-yield framework for studying and not a comprehensive textbook. Good luck with your studies!
–The First Aid/USMLE-Rx Team
CATEGORIES OF UPDATES
Corrections
Factual errors that interfere with comprehension
Minor Corrections
Less significant errors that may cause confusion
Suggestions & Clarifications
The text is accurate, but could be written more clearly
Minor formatting issues (misalignments, indents, etc.)
Helpful additions that improve the quality of a fact
NOTE: Entries with bolded/underlined page number are the newest additions to the official errata (also includes older entries that have been recently updated or reclassified).
CORRECTIONS
Page
Fact Name
Correction
72
tRNA
In the figure depicting tRNA charging, methionine should not be included on the left image. Amino acids such as methionine are covalently bound to the 3’ end of the tRNA by aminoacyl-tRNA synthetases.
102
Electron transport chain and oxidative phosphorylation
The arrow beneath “Complex V” should be facing upwards (to reflect movement of protons through the complex), not downward.
118
Bacterial structures
The chemical composition of the plasma membrane is best described as a phospholipid bilayer, not a lipoprotein bilayer.
135
E. Coli
In the entry for EIEC, in the second column, delete “No toxins produced.”
136
Salmonella vs. Shigella
Under the column for Shigella, note that antibiotic therapy shortens the duration of organism excretion (shedding) in the stool.
162
Hepatitis viruses
For the hepatitis D virus (HDV) entry, in the incubation column, note that co-infection represents an acute infection of both HBV and HDV and superinfection represents infection with HDV after developing chronic HBV.
221
Tumor suppressor genes
BRAF is a proto-oncogene, not a tumor suppressor gene.
231
G-protein–linked 2nd messengers
For the Gq-coupled receptor pathway, note that the role of phospholipase C is not to cleave lipids into PIP2, but rather to cleave PIP2 into both DAG and IP3 (one step downstream).
255
Cardiac and vascular function curves
For the graph, note that an acute, uncompensated hemorrhage would only result in a left shift of the volume curve; cardiac function is unchanged. See the new position of bullet point #3 below.
288
Insulin
(1) In the entry for regulation, note that growth hormone (GH) increases insulin resistance, leading indirectly to increased insulin secretion. It does not directly stimulate insulin release.
(2) Under the list of insulin regulators, note that β2-agonists, not antagonists, increase insulin secretion.
(3) In the image of a pancreatic β cell, note that glucose enters the cell via GLUT-2, not GLUT-1.
322
Pancreatic secretions
In the entry for trypsinogen, replace “creation of more trypsinogen” with “cleaving of other trypsinogen molecules into active trypsin.”
350
Pathologic RBC forms
In the entry for acanthocytes (spur cells), the image shown is actually an echinocyte (burr cell). Acanthocytes have irregularly spaced, longer projections (see image below) as compared to burr cells, whose projections are smaller and more uniformly spaced.
Image: Zamel, R et al. Abetalipoproteinemia: two case reports and literature review. Orphanet Journal of Rare Diseases 2008, 3:19. doi:10.1186/1750-1172-3-19
351
Other RBC pathologies
Under the entry for Heinz bodies, note that the mechanism for Heinz body formation is oxidation of hemoglobin sulfhydryl groups leading to denatured hemoglobin precipitation, not iron oxidation from the ferrous to the ferric form as we currently state.
361
Reed-Sternberg cells
It is the lymphocyte-rich variant of Hodgkin’s lymphoma that has the best long-term prognosis, not the nodular sclerosing form.
427
Spinal cord and associated tracts
The lateral spinothalamic tract label should be posterior and lateral to the anterior spinothalamic tract, as opposed to indicating the dorsal horn.
475
Tricyclic antidepressants
Desipramine has a lower (not higher) seizure threshold than the other TCAs.
525
Hydatidiform mole
For complete hydatidiform moles, the most common genetic makeup is an enucleated egg fertilized by a single sperm that subsequently duplicates the paternal DNA; an egg being fertilized by two distinct sperm is rare.
MINOR CORRECTIONS
Page
Fact Name
Correction
64
Chromatin structure
For the Histone methylation entry, please replace “Inactivates transcription of DNA” with “Can activate or repress transcription in a context-specific manner.” For the DNA methylation entry, please add “DNA methylation at CpG islands represses transcription” and move the mnemonic “Methylation makes DNA mute” to the DNA methylation row.
68
DNA replication
In the table entry for DNA ligase, please replace “phosphodiesterase” with “phosphodiester.”
77
Collagen
For the type III entry, replace the phrase in column 3 as follows: Type III: defective in Ehlers-Danlos syndrome, vascular type.
78
Osteogenesis imperfecta
Please note that in the most common type of OI (type I), the mutation leads to decreased production of otherwise normal type I collagen.
88
Autosomal trisomies
In the entry for Down syndrome, the last sentence of the third column should read, “Ultrasound shows ↑nuchal translucency in first trimester.”
113
Fatty acid metabolism
Replace the label “Inner mitochondrial membrane” with “Mitochondrial membranes.”
121
Obligate anaerobes
Actinomyces israelii is better classified as a facultative anaerobe, not an obligate one.
148
Protozoa – CNS infections
In the entry for transmission of Toxoplasma gondii, replace the first part of the first sentence with: “Cysts in meat or oocysts in cat feces.”
193
205
Sinusoids of spleen
Infections in immunodeficiency
For these two facts, add E. coli to the list of encapsulated organs and change the mnemonic to “ShiNE SkiS” (the E is for E. coli).
207
Immune deficiencies (cont.)
Wiskott-Aldrich syndrome is due to a defect in the WASP gene, not the WAS gene.
251
Interatrial septum development
In the text for step 5, note that the septum secundum, not the foramen secundum, enlarges.
294
Signaling pathways of endocrine hormones
To clarify, the IP3 pathway plays a minor role in GHRH signaling. The principal signaling pathway for GHRH is cAMP accumulation.
335
Budd-Chiari syndrome
Budd-Chiari syndrome is associated with hypercoagulable states (plural).
366
Langerhans cell histiocytosis
Delete “(neural crest origin)” from the second-to-last sentence of the second paragraph. Langerhans cells are of mesodermal origin, despite expressing the marker S-100.
406
Gout drugs
Please note that colchicine is primarily used clinically to treat acute gout rather than chronic gout.
494
Wilms’ tumor (nephroblastoma)
It is the WT2 gene (not WT1) that has a stronger association with Beckwith-Wiedemann syndrome.
505
Embryologic derivatives
The urethra is derived mostly from endoderm, not mesoderm.
521
Menstrual cycle
The arrow indicating when ovulation occurs should appear slightly after the LH surge, rather than before the LH surge.
576
Rapid review
The treatment for Sporothrix schenckii should be oral potassium iodide, not potassium chloride.
SUGGESTIONS & CLARIFICATIONS
Page
Fact Name
Suggestion/Clarification
60
Grief
In the entry for the onset of pathologic grief, replace “prolonged grief lasting > 2–6 months” with “prolonged grief lasting > 1 year” to make it consistent with the duration of normal bereavement (pathologic grief is normal bereavement that does not resolve within 1 year).
65
De novo pyrimidine and purine synthesis
This fact states that “Various antineoplastic and antibiotic drugs function by interfering with purine synthesis.” Please note that some of the drugs listed interfere with purine synthesis, while others interfere with pyrimidine synthesis.
78
Ehlers-Danlos syndrome
Delete the sentence “Type I or Type V collagen most frequently affected in severe classic Ehlers-Danlos syndrome” as this information goes beyond the scope of the Step I. Instead, replace it with the following high-yield clinical pearl: “May be confused with Marfan syndrome which is due to a defect in fibrillin, not collagen.”
79
Alport syndrome
Replace “Most common form is X-linked recessive” with “Most common form is X-linked; males are more severely affected than female carriers.”
82
Genetic terms
In the entry for Imprinting, please change the word “mutation” to “allele.”
83
Imprinting
(1) For Prader-Willi syndrome, change “Paternal allele is not expressed” to “Paternal (active) allele is deleted.”
(2) For Angelman syndrome, change “Maternal allele is not expressed” to “Maternal (active) allele is deleted.”
91
Vitamin B3 (niacin)
The synthesis of vitamin B3 (niacin) requires both vitamin B6 (pyridoxine) and vitamin B2 (riboflavin).
98
Summary of pathways
For the vitamin B12-dependent succinyl-CoA synthesis pathway, replace “Odd-chain fatty acids and branched-chain amino acids” with “Odd-chain fatty acids and the amino acids valine, isoleucine, methionine, and threonine.”
100
Glycolysis regulation, key enzymes
Under the box for glycolysis steps requiring ATP, replace “*Glucokinase in liver; hexokinase in all other tissues.” With “*Glucokinase in liver and β cells of pancreas; hexokinase in all other tissues.”
101
TCA cycle (Krebs cycle)
The calculation of 10 ATP produced per acetyl-CoA via the TCA cycle is based on 2.5 ATP per NADH, 1.5 ATP per FADH2, and 1 ATP per GTP.
102
Electron transport chain and oxidative phosphorylation
In the entry for ATP produced via ATP synthase, replace “1 NADH 3 ATP; 1 FADH2 2 ATP.” With “1 NADH 2.5 ATP; 1 FADH2 1.5 ATP.”
105
Sorbitol
Note that levels of sorbitol dehydrogenase in the lens of the eye, while present, are much lower than in the other tissue types listed.
108
Catecholamine synthesis/tyrosine catabolism
For the box labeled “Breakdown products via MAO and COMT,” update the contents as follows:
Dopamine HVA
Norepinephrine Normetanephrine VMA
Epinephrine Metanephrine VMA
121
Obligate aerobes
Pseudomonas aeruginosa may use some nitrogen-containing compounds (e.g., nitrates) as terminal electron acceptors for anaerobic metabolism in environments with low or absent oxygen.
154
Viral envelopes
Since picornavirus is an RNA virus and parvovirus is a DNA virus, the mnemonic makes more sense if the order of picornavirus and parvovirus is switched in the second column.
215
Leukocyte extravasation
In the entry for migration, under the second column, replace “bacterial products” with “products released in response to bacteria.”
238
β-blockers
Under the entry for MIs as an application of β-blockers, note that the specific agents shown to reduce mortality (per the COMET trial) are metoprolol, carvedilol, and bisoprolol.
258
Auscultation of the heart
Please refer to the updated heart murmurs chart shown below:
259
Heart murmurs
(1) For the description of the aortic stenosis murmur, replace “Radiates to carotids/heart base” with “Loudest at heart base; radiates to carotids.”
(2) In the entry for mitral valve prolapse, please replace the sentence “Loudest at S2” with “Loudest just before S2.”
(3) In the entry for mitral valve prolapse, please replace “Enhanced by maneuvers…” with “Occurs earlier with maneuvers…”
267
Patent ductus arteriosus
Please note that there are two key pathologic stages. In the neonatal period, lung resistance ↓ and the shunt becomes left to right. Untreated, the shunt may lead to RVH, LVH, and rarely heart failure. Uncorrected PDA with chronic overload of the pulmonary vasculature can eventually result in pulmonary hypertension and shunt reversal (Eisenmenger syndrome), manifesting as cyanosis and clubbing in the lower extremities (differential cyanosis).
281
Lipid-lowering agents
In the table entry for ezetimibe, please replace “reabsorption” with “absorption.”
291
Adrenal steroids
In the figure, please note that the primary source of both testosterone and DHT is not the zona reticularis. For testosterone, it is the testes; for DHT, it is peripheral tissues.
298
Hypothyroidism vs. hyperthyroidism
Myxedema (facial/periorbital) is correctly mentioned as associated with hypothyroidism. Note, however, that periorbital edema is also associated with hyperthyroidism.
301
SIADH
Note that hyponatremia in SIADH is secondary to increased water reabsorption; hypoaldosteronism is a compensatory response to maintain volume status which has the undesired effect of increased Na+ excretion.
302
Diabetes mellitus
(1) In the entry for acute manifestations, in the second column, please add “can be caused by” before the “unopposed secretion of GH” (diabetes does not cause unopposed secretion of GH).
(2) In the entry for chronic manifestations, in the second paragraph, please replace “(sorbitol accumulation in organs with aldose reductase)” with “(sorbitol accumulation in organs with aldose reductase and low or absent sorbitol dehydrogenase).”
(3) In the entry for chronic manifestations, in the first bullet point, replace “arteriosclerosis leading to hypertension” with “arteriolosclerosis leading to hypertension,” which better reflects the small vessel nature of the disease process.
304
Multiple endocrine neoplasias (MEN)
Please note that MEN 2A is associated with parathyroid hyperplasia, not parathyroid adenomas.
326
Celiac sprue
Replace “↓ mucosal absorption that primarily affects jejunum” with
“↓ mucosal absorption that primarily affects distal duodenum and/or proximal jejunum.”
336
Hereditary hyperbilirubinemias
In the entry for Gilbert’s syndrome, in the second column, replace the first sentence with the following: “Mildly ↓ UDP-glucuronyl transferase conjugation activity leading to ↓ bilirubin uptake by hepatocytes.”
352
Microcytic, hypochromic (MCV < 80 fL) anemia
(1) In the entry for α-thalassemia, first sentence of second column, replace “α-globin gene mutations” with “α-globin gene deletions” to better reflect the genetic defect.
(2) In the third column, replace all instances of “gene” with “allele.”
357
Extrinsic hemolytic normocytic anemia
(1) For the indirect Coombs’ test, to trigger the reaction, anti-IgG antibodies (Coombs’ reagent) must be added after the RBCs are added to the patient’s serum.
(2) For the direct Coombs’ test, note that anti-Ig antibodies are added to the patient’s blood, not serum.
360
Hereditary thrombosis syndromes leading to hypercoagulability
For antithrombin deficiency, please replace “↑ in PTT is blunted after heparin administration” with “PTT normalizes after heparin administration.”
366
Chronic myeloproliferative disorders
In the entry for chronic myeloproliferative disorders, please replace “constitutively active JAK2 receptors” with “constitutively active JAK-STAT signaling pathway” (JAK2 is a non-receptor tyrosine kinase).
371
Antimetabolites
In the “Azathioprine, 6-mercaptopurine (6-MP), 6-thioguanine (6-TG)” entry, for toxicities, note that only 6-MP toxicity increases with allopurinol administration (6-TG is broken down by an alternative deamination mechanism and its metabolism is not affected by allopurinol).
373
Microtubule inhibitors
In the entry for vincristine and vinblastine, the mechanism of action affects both the S phase and the M phase of the cell cycle.
382
Upper extremity nerves
For the radial nerve and median nerve territories, “(C5–T1)” and “(C5–C8, T1)” mean the same thing.
418
Homunculus
In the homunculus image, we do not show the sensory distribution of the abdomen and genitalia.
422
Effects of strokes
With a PICA (lateral medullary) stroke, there is ipsilateral loss of facial pain/temperature sensation and contralateral loss of body pain/temperature sensation.
425
Ischemic brain disease/stroke
The definition of a transient ischemic attack is an episode of focal neurological dysfunction lasting < 24 hours. The majority of attacks resolve prior to 1 hour.
437
Facial lesions
In the diagram, remove the arrows associated with the green lines that point toward the cerebral cortex; CN VII is predominantly efferent.
438
Common eye conditions
Accommodation is not an eye condition, but rather a normal physiological function to focus on near objects.
439
Extraocular muscles and nerves
Patients with a CN IV palsy will tilt their head in the contralateral direction as a compensatory mechanism. Tilting the head in the ipsilateral direction worsens the vertical eye deviation, as stated in the book.
446
Neurocutaneous disorders
Sturge-Weber syndrome can be associated with either hemiparesis or hemiplegia.
502
ACE inhibitors
In the third column, angiotensin II receptor blockers have a reduced (rather than absent) risk of cough/angioedema.
515
Female reproductive epithelial histology
Note that the stratified squamous epithelium of the ectocervix is also nonkeratinized.
517
Seminiferous tubules
To clarify, in the line drawing, the size of primary spermatocytes is generally equal to that of spermatogonia, not smaller.
528
Cervical pathology
Replace the third sentence of the second column with the following: “Associated with HPV 16 and HPV 18, which produce both the E6 gene product (inhibits p53 suppressor gene) and E7 gene product (inhibits RB suppressor gene).”
545
Diaphragm structures
In the third column, the spelling of “esophagus” should be changed to “oesophagus” to make the mnemonic for “10 letters at T10” valid.
563
Asthma drugs
In the entry for methylxanthines, replace “thereby ↓ cAMP hydrolysis” with “thereby resulting in ↑ cAMP levels due to ↓ cAMP hydrolysis.”
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