Evaluation of a course to prepare international students for the United States Medical Licensing Examination step 2 clinical skills exam

PURPOSE

United States (US) and Canadian citizens attending medical school abroad often desire to return to the US for residency, and therefore must pass US licensing exams. We describe a 2-day United States Medical Licensing Examination (USMLE) step 2 clinical skills (CS) preparation course for students in the Technion American Medical School program (Haifa, Israel) between 2012 and 2016.

METHODS

Students completed pre- and post-course questionnaires. The paired t-test was used to measure students' perceptions of knowledge, preparation, confidence, and competence in CS pre- and post-course. To test for differences by gender or country of birth, analysis of variance was used. We compared USMLE step 2 CS pass rates between the 5 years prior to the course and the 5 years during which the course was offered.

RESULTS

Ninety students took the course between 2012 and 2016. Course evaluations began in 2013. Seventy-three students agreed to participate in the evaluation, and 64 completed the pre- and post-course surveys. Of the 64 students, 58% were US-born and 53% were male. Students reported statistically significant improvements in confidence and competence in all areas. No differences were found by gender or country of origin. The average pass rate for the 5 years prior to the course was 82%, and the average pass rate for the 5 years of the course was 89%.

CONCLUSION

A CS course delivered at an international medical school may help to close the gap between the pass rates of US and international medical graduates on a high-stakes licensing exam. More experience is needed to determine if this model is replicable.

Conservation within the RIC-3 gene family. Effectors of mammalian nicotinic acetylcholine receptor expression

In Caenorhabditis elegans, the ric-3 gene is required for the maturation of multiple nicotinic acetylcholine receptors (nAChRs), whereas other neurotransmittergated channels expressed within the same cells are unaffected by the presence of RIC-3. Here we show that RIC-3 is a member of a conserved gene family with representatives in both vertebrates and invertebrates. All members of this family have two transmembrane domains followed by a coiled-coil domain. Expression of the human ric-3 homolog, hric3, like the C. elegans ric-3, enhances C. elegans DEG-3/DES-2, rat alpha 7, and human alpha 7 nAChR-dependent whole-cell current amplitudes in Xenopus leavis oocytes, thus demonstrating functional conservation. However, hric3 also reduces human alpha 4 beta 2 and alpha 3 beta 4 nAChR-dependent whole-cell current amplitudes. Thus, hric3 shows differential effects on human nAChRs unlike the observed uniform effect of ric-3 on C. elegans nAChRs. Moreover, hric3 totally abolished currents evoked by 5-HT3 serotonin receptors, whereas it barely modified alpha1 glycine receptor currents. With this caveat, RIC-3 belongs to a conserved family of genes likely to regulate nAChR-mediated transmission throughout evolution. Analysis of transcripts encoded by the hric3 locus shows that it encodes for multiple transcripts, likely to produce multiple hric3 isoforms, and that hric3 is expressed in neurons and muscles, thus enabling its interactions with nAChRs in vivo.

Mutations in the extracellular domain and in the membrane-spanning domains interfere with nicotinic acetylcholine receptor maturation

The deg-3(u662) mutation is a degeneration-causing mutation in a Caenorhabditis elegans nicotinic acetylcholine receptor. In a large screen for mutations that suppress the deleterious effects of this mutation we identified 32 mutations in the deg-3 gene. Among these, 11 are missense mutations, affecting seven residues within the extracellular domain or the membrane-spanning domains. All of these mutations greatly reduce the degeneration-causing activity of deg-3(u662). All but one of these mutations cause defective localization of the DEG-3 protein, as seen in immunohistochemical analysis. Thus our screen identifies multiple residues within the nicotinic acetylcholine receptor needed for normal folding, assembly, or trafficking of this receptor. Interestingly, these mutations lead to distinct localization defects suggesting differences in their effect on DEG-3's maturation process. Specifically, mutations in the extracellular domain lead to a phenotype more severe than mutations in the membrane-spanning domains. Differences in the effects of the mutations are also predicted by homology-based modeling, showing that some mutations in the extracellular domain are likely to disrupt the native fold of the protein, while others are likely to disrupt trafficking.

The C. elegans ric-3 gene is required for maturation of nicotinic acetylcholine receptors

Mutations in ric-3 (resistant to inhibitors of cholinesterase) suppress the neuronal degenerations caused by a gain of function mutation in the Caenorhabditis elegans DEG-3 acetylcholine receptor. RIC-3 is a novel protein with two transmembrane domains and extensive coiled-coil domains. It is expressed in both muscles and neurons, and the protein is concentrated within the cell bodies. We demonstrate that RIC-3 is required for the function of at least four nicotinic acetylcholine receptors. However, GABA and glutamate receptors expressed in the same cells are unaffected. In ric-3 mutants, the DEG-3 receptor accumulates in the cell body instead of in the cell processes. Moreover, co-expression of ric-3 in Xenopus laevis oocytes enhances the activity of the C.elegans DEG-3/DES-2 and of the rat alpha-7 acetylcholine receptors. Together, these data suggest that RIC-3 is specifically required for the maturation of acetylcholine receptors.

Characterization of the deg-3/des-2 receptor: a nicotinic acetylcholine receptor that mutates to cause neuronal degeneration

The nicotinic acetylcholine receptor family (nAChR) is a large family of acetylcholine-gated cation channels. Here we characterize the Caenorhabditis elegans DEG-3/DES-2 nAChR, a receptor identified due to its involvement in neuronal degeneration. Pharmacological analysis of a DEG-3/DES-2 receptor expressed in Xenopus oocytes shows that this receptor is preferentially activated by choline. This choline sensitivity of the DEG-3/DES-2 channel can explain its role in neuronal degeneration, as shown by the toxic effects of choline on oocytes expressing the mutant DEG-3/DES-2 channel. We also show that in C. elegans the DEG-3/DES-2 receptor is localized to nonsynaptic regions, including the sensory endings of chemosensory neurons. This localization is in agreement with a role for this receptor in chemosensation of choline, as inferred from a defect in chemotaxis for choline seen in deg-3 mutants. Thus, this work also provides evidence for the diversity of nonsynaptic activities associated with nAChRs.

Antibodies from ALS patients inhibit dopamine release mediated by L-type calcium channels

OBJECTIVE

To examine the presence of anti-L-type calcium channel antibodies in the serum of ALS patients.

BACKGROUND

Autoimmunity has been hypothesized as one of the mechanisms underlying the pathogenesis of sporadic ALS. Previous studies reported that sera from patients with sporadic ALS contain antibodies against voltage-gated calcium channels (L-type and P-type), but others do not support these findings.

METHODS

Regulated secretion of tritiated dopamine ([3H]DA) in PC12 cells is mediated exclusively by calcium entry through L-type calcium channels. To examine whether purified ALS immunoglobulin G (IgG) inhibits [3H]DA release by interfering with calcium entry through L-type calcium channels, evoked release in PC12 cells was determined in the presence of ALS IgG. This functional assay provides a sensitive way to examine L-type calcium channel interaction with IgG from ALS patients.

RESULTS

A significant inhibition of depolarization-evoked [3H]DA release (32+/-4%) was observed by purified IgG from ALS patients compared with control subjects (11+/-2%; p < 0.01). Significant inhibition by IgG occurred in 79% (15/19) of the ALS patients compared with only 29% (5/17) in the control group (p < 0.01). The level of calcium channel inhibition by ALS IgG correlated positively with disease duration (r = 0.68; p < 0.01) and correlated negatively with age (r = -0.48; p < 0.05).

CONCLUSIONS

These results confirm the presence of antibodies against the L-type calcium channel in the majority of sera from ALS patients, supporting their role in the pathogenesis of ALS.

The alpha 2/delta subunit of voltage sensitive Ca2+ channels is a single transmembrane extracellular protein which is involved in regulated secretion

The membrane topology of alpha 2/delta subunit was investigated utilizing electrophysiological functional assay and specific anti-alpha 2 antibodies. (a) cRNA encoding a deleted alpha 2/delta subunit was coinjected with alpha 1C subunit of the L-type calcium channel into Xenopus oocytes. The truncated form, lacking the third putative TM domain (alpha 2/delta delta TMIII), failed to amplify the expressed inward currents, normally induced by alpha 1C coinjected with intact alpha 2/delta subunit. Western blot analysis of alpha 2/delta delta TMIII shows the appearance of a degraded alpha 2 protein and no expression of the full-size two-TM truncated-protein. The improper processing of alpha 2/delta delta TMIII suggests that the alpha 2/delta is a single TM domain protein and the TM region is positioned at the delta subunit. (b) External application of anti-alpha 2 antibodies, prepared for an epitope within the alternatively spliced and 'intracellular' region, inhibits depolarization induced secretion in PC12, further supporting an external location of the alpha 2 subunit and establishing delta subunit as the only membrane anchor for the extracellular alpha 2 subunit.

Identification of the alternative spliced form of the alpha 2/delta subunit of voltage sensitive Ca2+ channels expressed in PC12 cells

The alpha 2/delta subunit of voltage sensitive Ca2+ channels expressed in PC12 has been cloned and partially sequenced. The message observed in Northern blot analysis displays a 7.5 kb transcript, identical in size to mRNA of rabbit skeletal muscle and rat brain. The nucleotide sequence of the cloned alpha 2 subunit of the PC12 specific cDNA is > 99% identical to rat brain sequence and 85% to skeletal muscle. Reverse-transcriptase-polymerase chain reaction (RT-PCR) of the alternative splicing region identifies two deleted regions of 57 bp and 21 bp in PC12 expressed alpha 2/delta transcript. The alternative variant alpha 2e of alpha 2/delta subunit which is expressed in PC12 cells was previously identified in human embryonic kidney (HEK293) cells. RT-PCR analysis show two different sized alternative PCR fragments in rat lung and none in rat spleen, kidney and intestine. Antibodies prepared against a 19 amino acid peptide within the alternative spliced region effectively inhibits [3H]dopamine release in PC12 cells. This implies that the alternatively spliced region is positioned extracellularly and is involved in regulation of the L-type Ca2+ channel-mediated transmitter release.