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Focal segmental glomerulosclerosis
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<h2 id="signs-and-symptoms">Signs and symptoms</h2> <p>The most common symptoms are a result of abnormal loss of protein from the <a href="/facts/Glomerulus_(kidney)/rlRXJsJy">glomerulus</a> of the kidney, and include:<a class="footnote-ref" id="fnref:19" href="#fn:19"><sup>19</sup></a><a class="footnote-ref" id="fnref:20" href="#fn:20"><sup>20</sup></a> </p> <ul><li>Frothy urine (due to excess protein)</li> <li>Excess water retention (pitting <a href="/facts/Edema/Q6MI3KdH">edema</a>, due to loss of serum <a href="/facts/Albumin/gDmSgAH2">albumin</a>)</li> <li>Susceptibility to infection (due to loss of serum <a href="/facts/Antibody/MX8pdTdP">antibodies</a>)</li></ul> <p>Common signs are also due to loss of blood proteins by the glomerulus of the kidney, including:<a class="footnote-ref" id="fnref:21" href="#fn:21"><sup>21</sup></a><a class="footnote-ref" id="fnref:22" href="#fn:22"><sup>22</sup></a><a class="footnote-ref" id="fnref:23" href="#fn:23"><sup>23</sup></a> </p> <ul><li><a href="/facts/Proteinuria/cFXX8w1F">Protein in the urine</a> (often in the <a href="/facts/Nephrotic_syndrome/YG7bUzWV">nephrotic syndrome</a>-range of >3.5 g/day)</li> <li><a href="/facts/Hypoalbuminemia/sJD2mV5w">Low serum albumin</a> (<3.5 g/dl)</li> <li><a href="/facts/Hypogammaglobulinemia/hRgNUwG7">Low serum antibodies</a></li> <li><a href="/facts/Hypercholesterolemia/UlIDdQuT">High serum cholesterol</a> (compensatory by the liver to compensate for low serum <a href="/facts/Oncotic_pressure/d1YAUqmF">oncotic pressure</a>)</li> <li><a href="/facts/Urinary_cast/V5eU9PrG">Fatty casts</a> in the urine (secondary to hypercholesterolemia)</li></ul> <h2 id="pathophysiology">Pathophysiology</h2> <p>FSGS is primarily a disease of the renal <a href="/facts/Glomerulus_(kidney)/rlRXJsJy">glomerulus</a>, the site of filtration of ions and solutes.<a class="footnote-ref" id="fnref:24" href="#fn:24"><sup>24</sup></a><a class="footnote-ref" id="fnref:25" href="#fn:25"><sup>25</sup></a> <a href="/facts/Podocyte/QnFbjc96">Podocytes</a> are specialized cells lining the <a href="/facts/Bowman%2527s_capsule/mvJx1IEJ">Bowman's capsule</a> that contribute to the filtration barrier, preventing molecules larger than 5 <a href="/facts/Nanometre/a98sjHyu">nm</a> from being filtered.<a class="footnote-ref" id="fnref:26" href="#fn:26"><sup>26</sup></a> FSGS involves damage to the renal podocytes such that larger molecules, most notably proteins, are filtered and lost through the kidney.<a class="footnote-ref" id="fnref:27" href="#fn:27"><sup>27</sup></a><a class="footnote-ref" id="fnref:28" href="#fn:28"><sup>28</sup></a> Thus, many of the signs and symptoms of FSGS are related to protein loss.<a class="footnote-ref" id="fnref:29" href="#fn:29"><sup>29</sup></a> </p><p>On histology, FSGS manifests as scarring (<a href="/facts/Sclerosis_(medicine)/KPhDDorL">sclerosis</a>) to segments of glomeruli; moreover, only a portion of glomeruli are affected.<a class="footnote-ref" id="fnref:30" href="#fn:30"><sup>30</sup></a><a class="footnote-ref" id="fnref:31" href="#fn:31"><sup>31</sup></a><a class="footnote-ref" id="fnref:32" href="#fn:32"><sup>32</sup></a> The focal and segmental nature of disease seen on histology help to distinguish FSGS from other types of <a href="/facts/Glomerulosclerosis/xIYHrtYN">glomerular sclerosis</a>.<a class="footnote-ref" id="fnref:33" href="#fn:33"><sup>33</sup></a> </p><p>FSGS can be classified by the putative cause of damage to podocytes. Primary FSGS involves cases in which no cause is readily identifiable.<a class="footnote-ref" id="fnref:34" href="#fn:34"><sup>34</sup></a> It is presumed that a set of unidentified circulating factors in the blood contribute to podocyte damage in these cases.<a class="footnote-ref" id="fnref:35" href="#fn:35"><sup>35</sup></a><a class="footnote-ref" id="fnref:36" href="#fn:36"><sup>36</sup></a> </p><p>Secondary FSGS is caused by an identifiable stress or toxin that injures podocytes.<a class="footnote-ref" id="fnref:37" href="#fn:37"><sup>37</sup></a> Many causes of secondary FSGS contribute to podocyte injury through hyperfiltration, which is a scenario of excess filtration by renal glomeruli.<a class="footnote-ref" id="fnref:38" href="#fn:38"><sup>38</sup></a> Hyperfiltration can be caused by obesity, diabetes or loss of the contralateral kidney, among other causes.<a class="footnote-ref" id="fnref:39" href="#fn:39"><sup>39</sup></a> </p><p>Secondary FSGS can also be caused by toxins, including anabolic steroids and heroin.<a class="footnote-ref" id="fnref:40" href="#fn:40"><sup>40</sup></a><a class="footnote-ref" id="fnref:41" href="#fn:41"><sup>41</sup></a> </p><p>A number of genes have been implicated in FSGS. These include: <i>NPHS1</i>, which encodes the protein <a href="/facts/Nephrin/lmHtsa3L">nephrin</a> that contributes to the filtration barrier;<a class="footnote-ref" id="fnref:42" href="#fn:42"><sup>42</sup></a> <i>NPHS2</i>, which encodes the protein <a href="/facts/Podocin/M5kVnUQp">podocin</a> found in podocytes;<a class="footnote-ref" id="fnref:43" href="#fn:43"><sup>43</sup></a> and <i>INF2</i>, which encodes the actin-binding protein <a href="/facts/Formins/c6wajXx4">formin</a>.<a class="footnote-ref" id="fnref:44" href="#fn:44"><sup>44</sup></a> </p><p>The pathogenesis of HIV-associated FSGS is unclear, but may be due to the presence of the G1/G2 risk alleles of the <a href="/facts/APOL1/zEK3Abo2">APOL1</a> gene. There is some data to suggest that HIV can infect tubular epithelial cells and podocytes, but much remains to be known.<a class="footnote-ref" id="fnref:45" href="#fn:45"><sup>45</sup></a> </p><p><a href="/facts/Gain_of_function_mutation/Ee4NnWbY">Gain of function mutations</a> in <a href="/facts/APOL1/zEK3Abo2">APOL1</a> have also been proposed to play a role in the pathogenesis of this disease.<a class="footnote-ref" id="fnref:46" href="#fn:46"><sup>46</sup></a> </p> <h2 id="diagnosis">Diagnosis</h2> <p>Diagnosis of FSGS is made by <a href="/facts/Renal_biopsy/J9ypIQDa">renal biopsy</a> that includes at least fifteen serial cuts with at least eight <a href="/facts/Glomeruli/C7VsNqPJ">glomeruli</a>.<a class="footnote-ref" id="fnref:47" href="#fn:47"><sup>47</sup></a><a class="footnote-ref" id="fnref:48" href="#fn:48"><sup>48</sup></a> Histologic features include <a href="/facts/Sclerosis_(medicine)/KPhDDorL">sclerosis</a> (scarring) of a portion (average: 15%) of the glomerular space, with only a portion of glomeruli manifesting any sclerosis.<a class="footnote-ref" id="fnref:49" href="#fn:49"><sup>49</sup></a> </p><p>Other tests helpful in the diagnosis include urine protein, urinalysis, serum albumin, and serum lipids.<a class="footnote-ref" id="fnref:50" href="#fn:50"><sup>50</sup></a> A clinical picture of <a href="/facts/Proteinuria/cFXX8w1F">proteinuria</a>, low blood protein levels (albumin, antibodies), and high blood cholesterol would support a diagnosis of FSGS, although these do not help to distinguish between FSGS and other causes of proteinuria.<a class="footnote-ref" id="fnref:51" href="#fn:51"><sup>51</sup></a><a class="footnote-ref" id="fnref:52" href="#fn:52"><sup>52</sup></a> </p> <h3>Classification</h3> <p>Five mutually exclusive variants of focal segmental glomerulosclerosis may be distinguished by the pathologic findings seen on <a href="/facts/Renal_biopsy/J9ypIQDa">renal biopsy</a>:<a class="footnote-ref" id="fnref:53" href="#fn:53"><sup>53</sup></a> </p> <ol><li>Collapsing variant</li> <li>Glomerular tip lesion variant</li> <li>Cellular variant</li> <li>Perihilar variant</li> <li>Not otherwise specified (NOS) variant</li></ol> <p>Recognition of these variants may have <a href="/facts/Prognosis/3DEGwPag">prognostic</a> value in individuals with primary focal segmental glomerulosclerosis. The collapsing variant is associated with higher rate of progression to <a href="/facts/End-stage_renal_disease/4YKH9wpo">end-stage renal disease</a>, whereas the glomerular tip lesion variant has a low rate of progression to end-stage renal disease in most patients.<a class="footnote-ref" id="fnref:54" href="#fn:54"><sup>54</sup></a> The cellular variant shows similar clinical presentation to collapsing and glomerular tip variant but has intermediate outcomes between the other two variants.<a class="footnote-ref" id="fnref:55" href="#fn:55"><sup>55</sup></a> </p> <h2 id="treatment">Treatment</h2> <p>First-line treatment for primary FSGS consists of anti-inflammatory drugs.<a class="footnote-ref" id="fnref:56" href="#fn:56"><sup>56</sup></a> Specifically, <a href="/facts/Glucocorticoid/2P91Aj3S">glucocorticoids</a> are begun in patients manifesting with <a href="/facts/Nephrotic_syndrome/YG7bUzWV">nephrotic</a>-range proteinuria (>3.5 g/day).<a class="footnote-ref" id="fnref:57" href="#fn:57"><sup>57</sup></a><a class="footnote-ref" id="fnref:58" href="#fn:58"><sup>58</sup></a> For patients who maintain nephrotic-range proteinuria despite glucocorticoids, or for patients who demonstrate glucocorticoid intolerance, <a href="/facts/Calcineurin_inhibitors/ctlB3Hda">calcineurin inhibitors</a> (e.g., tacrolimus) are initiated.<a class="footnote-ref" id="fnref:59" href="#fn:59"><sup>59</sup></a> Successful treatment is defined as a drop in proteinuria to sub-nephrotic ranges.<a class="footnote-ref" id="fnref:60" href="#fn:60"><sup>60</sup></a> </p><p>The treatment of secondary FSGS involves addressing the particular toxic or stress agent.<a class="footnote-ref" id="fnref:61" href="#fn:61"><sup>61</sup></a> </p> <h2 id="prognosis">Prognosis</h2> <p>The majority of untreated cases of FSGS will progress to <a href="/facts/Chronic_kidney_disease/4YKH9wpo">end-stage kidney disease</a>.<a class="footnote-ref" id="fnref:62" href="#fn:62"><sup>62</sup></a> Important prognostic factors include the degree of <a href="/facts/Proteinuria/cFXX8w1F">proteinuria</a> and initial response to therapy. </p><p>Patients with <a href="/facts/Nephrotic_syndrome/YG7bUzWV">nephrotic</a>-range (>3.5 g/day) proteinuria have over a 50% rate of progression to end-stage kidney disease at 10 years.<a class="footnote-ref" id="fnref:63" href="#fn:63"><sup>63</sup></a> Only 15% of patients with sub-nephrotic ranges of proteinuria progress to end-stage renal failure at 10 years.<a class="footnote-ref" id="fnref:64" href="#fn:64"><sup>64</sup></a> </p><p>Initial response to therapy also dictates long-term outcomes. Those defined as having a "complete response" typically manifest a proteinuria of <300 mg/day; those with a "partial response" manifest a sub-nephrotic range of proteinuria, <3.5 g/day.<a class="footnote-ref" id="fnref:65" href="#fn:65"><sup>65</sup></a> Either complete or partial response is associated with 80% kidney survival at 10 years, compared with about 50% among non-responsive patients.<a class="footnote-ref" id="fnref:66" href="#fn:66"><sup>66</sup></a> </p> <h2 id="epidemiology">Epidemiology</h2> <p>FSGS accounts for 35% of all cases of <a href="/facts/Nephrotic_syndrome/YG7bUzWV">nephrotic syndrome</a>, making it one of the most common causes of nephrotic syndrome in the United States.<a class="footnote-ref" id="fnref:67" href="#fn:67"><sup>67</sup></a> FSGS accounts for 2% of all cases of kidney failure.<a class="footnote-ref" id="fnref:68" href="#fn:68"><sup>68</sup></a> African American patients have four times the likelihood of developing FSGS. Men are about two times as likely to develop FSGS compared to women.<a class="footnote-ref" id="fnref:69" href="#fn:69"><sup>69</sup></a> </p> <h2 id="notable-cases">Notable cases</h2> <ul><li><a href="/facts/Andy_Cole/NzjUoESs">Andy Cole</a></li> <li><a href="/facts/Gary_Coleman/wQ6bFuVI">Gary Coleman</a></li> <li><a href="/facts/Sean_Elliott/hxBDnvwK">Sean Elliott</a></li> <li><a href="/facts/Alonzo_Mourning/vnTScc2f">Alonzo Mourning</a></li></ul> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Glomerulonephritis/HasrFC92">Glomerulonephritis</a></li> <li><a href="/facts/Nephrotic_syndrome/YG7bUzWV">Nephrotic syndrome</a></li></ul> <h2 id="external-links">External links</h2> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Rosenberg AZ, Kopp JB (March 2017). "Focal Segmental Glomerulosclerosis". Clin J Am Soc Nephrol. 12 (3): 502–517. doi:10.2215/CJN.05960616. PMC 5338705. PMID 28242845. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5338705" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5338705</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>D'Agati V (October 1994). "The many masks of focal segmental glomerulosclerosis". Kidney Int. 46 (4): 1223–41. doi:10.1038/ki.1994.388. PMID 7861720. <a href="https://doi.org/10.1038%2Fki.1994.388" target="_blank">https://doi.org/10.1038%2Fki.1994.388</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>D'Agati V (October 1994). "The many masks of focal segmental glomerulosclerosis". Kidney Int. 46 (4): 1223–41. doi:10.1038/ki.1994.388. PMID 7861720. <a href="https://doi.org/10.1038%2Fki.1994.388" target="_blank">https://doi.org/10.1038%2Fki.1994.388</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Kitiyakara C, Eggers P, Kopp JB (November 2004). "Twenty-one-year trend in ESRD due to focal segmental glomerulosclerosis in the United States". Am J Kidney Dis. 44 (5): 815–25. doi:10.1016/S0272-6386(04)01081-9. PMID 15492947. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Rosenberg AZ, Kopp JB (March 2017). "Focal Segmental Glomerulosclerosis". Clin J Am Soc Nephrol. 12 (3): 502–517. doi:10.2215/CJN.05960616. PMC 5338705. PMID 28242845. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5338705" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5338705</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Rydel JJ, Korbet SM, Borok RZ, Schwartz MM (April 1995). "Focal segmental glomerular sclerosis in adults: presentation, course, and response to treatment". Am J Kidney Dis. 25 (4): 534–42. doi:10.1016/0272-6386(95)90120-5. PMID 7702047. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>Rydel JJ, Korbet SM, Borok RZ, Schwartz MM (April 1995). "Focal segmental glomerular sclerosis in adults: presentation, course, and response to treatment". Am J Kidney Dis. 25 (4): 534–42. doi:10.1016/0272-6386(95)90120-5. PMID 7702047. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>Korbet SM, Schwartz MM, Lewis EJ (June 1994). "Primary focal segmental glomerulosclerosis: clinical course and response to therapy". Am J Kidney Dis. 23 (6): 773–83. doi:10.1016/s0272-6386(12)80128-4. PMID 8203357. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>"Focal segmental glomerulosclerosis (FSGS)". www.kidneyfund.org. 2021-10-28. Retrieved 2023-11-14. <a href="https://www.kidneyfund.org/all-about-kidneys/other-kidney-diseases/focal-segmental-glomerulosclerosis-fsgs" target="_blank">https://www.kidneyfund.org/all-about-kidneys/other-kidney-diseases/focal-segmental-glomerulosclerosis-fsgs</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>Haas M, Meehan SM, Karrison TG, Spargo BH (November 1997). "Changing etiologies of unexplained adult nephrotic syndrome: a comparison of renal biopsy findings from 1976–1979 and 1995–1997". Am J Kidney Dis. 30 (5): 621–31. doi:10.1016/s0272-6386(97)90485-6. PMID 9370176. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>Fogo AB (February 2015). "Causes and pathogenesis of focal segmental glomerulosclerosis". Nat Rev Nephrol. 11 (2): 76–87. doi:10.1038/nrneph.2014.216. PMC 4772430. PMID 25447132. <a href="/wiki/Agnes_Fogo" target="_blank">/wiki/Agnes_Fogo</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>Rosenberg AZ, Kopp JB (March 2017). "Focal Segmental Glomerulosclerosis". Clin J Am Soc Nephrol. 12 (3): 502–517. doi:10.2215/CJN.05960616. PMC 5338705. PMID 28242845. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5338705" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5338705</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>Kiffel J, Rahimzada Y, Trachtman H (September 2011). "Focal segmental glomerulosclerosis and chronic kidney disease in pediatric patients". Adv Chronic Kidney Dis. 18 (5): 332–8. doi:10.1053/j.ackd.2011.03.005. PMC 3709971. PMID 21896374. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3709971" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3709971</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li> <li id="fn:14"><p>Campbell KN, Tumlin JA (2018). "Protecting Podocytes: A Key Target for Therapy of Focal Segmental Glomerulosclerosis". Am J Nephrol. 47 (Suppl 1): 14–29. doi:10.1159/000481634. PMC 6589822. PMID 29852493. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6589822" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6589822</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></p></li> <li id="fn:15"><p>Rydel JJ, Korbet SM, Borok RZ, Schwartz MM (April 1995). "Focal segmental glomerular sclerosis in adults: presentation, course, and response to treatment". Am J Kidney Dis. 25 (4): 534–42. doi:10.1016/0272-6386(95)90120-5. PMID 7702047. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></p></li> <li id="fn:16"><p>Tucker JK (February 2002). "Focal segmental glomerulosclerosis in African Americans". Am J Med Sci. 323 (2): 90–3. doi:10.1097/00000441-200202000-00006. PMID 11863085. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:16" class="footnote-back-ref">↩</a></p></li> <li id="fn:17"><p>Kitiyakara C, Kopp JB, Eggers P (March 2003). "Trends in the epidemiology of focal segmental glomerulosclerosis". Semin Nephrol. 23 (2): 172–82. doi:10.1053/snep.2003.50025. PMID 12704577. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:17" class="footnote-back-ref">↩</a></p></li> <li id="fn:18"><p>"Focal segmental glomerulosclerosis (FSGS)". www.kidneyfund.org. 2021-10-28. Retrieved 2023-11-14. <a href="https://www.kidneyfund.org/all-about-kidneys/other-kidney-diseases/focal-segmental-glomerulosclerosis-fsgs" target="_blank">https://www.kidneyfund.org/all-about-kidneys/other-kidney-diseases/focal-segmental-glomerulosclerosis-fsgs</a> <a href="#fnref:18" class="footnote-back-ref">↩</a></p></li> <li id="fn:19"><p>Rosenberg AZ, Kopp JB (March 2017). "Focal Segmental Glomerulosclerosis". Clin J Am Soc Nephrol. 12 (3): 502–517. doi:10.2215/CJN.05960616. PMC 5338705. PMID 28242845. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5338705" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5338705</a> <a href="#fnref:19" class="footnote-back-ref">↩</a></p></li> <li id="fn:20"><p>Rydel JJ, Korbet SM, Borok RZ, Schwartz MM (April 1995). "Focal segmental glomerular sclerosis in adults: presentation, course, and response to treatment". Am J Kidney Dis. 25 (4): 534–42. doi:10.1016/0272-6386(95)90120-5. PMID 7702047. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:20" class="footnote-back-ref">↩</a></p></li> <li id="fn:21"><p>Rosenberg AZ, Kopp JB (March 2017). "Focal Segmental Glomerulosclerosis". Clin J Am Soc Nephrol. 12 (3): 502–517. doi:10.2215/CJN.05960616. PMC 5338705. PMID 28242845. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5338705" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5338705</a> <a href="#fnref:21" class="footnote-back-ref">↩</a></p></li> <li id="fn:22"><p>Rydel JJ, Korbet SM, Borok RZ, Schwartz MM (April 1995). "Focal segmental glomerular sclerosis in adults: presentation, course, and response to treatment". Am J Kidney Dis. 25 (4): 534–42. doi:10.1016/0272-6386(95)90120-5. PMID 7702047. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:22" class="footnote-back-ref">↩</a></p></li> <li id="fn:23"><p>Kiffel J, Rahimzada Y, Trachtman H (September 2011). 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