AssessmentsJuvenile polyposis syndrome
Juvenile polyposis syndrome
Juvenile polyposis syndrome is an (X-linked/autosomal) dominant disease.
USMLE® Step 1 style questions USMLE
USMLE® Step 2 style questions USMLE
A 19-year-old man comes to the urgent care clinic because he has seen blood in the toilet for the past 4 days. He has also had worsening abdominal pain for the past two weeks. He has not had a fever, nausea, or vomiting. He has not had any diarrhea or constipation. He has no significant past medical history. There is no history of GI problems on his mother's side, but the patient does not know anything about his father's side of the family. The patient's vitals are stable, though a complete blood count shows a hemoglobin of 9.2g/dL with a mean corpuscular volume of 75 μm3. He is sent for a colonoscopy which shows numerous hamartous polyps. These findings are most consistent with which of the following diagnoses?
In juvenile polyposis syndrome, young children develop multiple polyps throughout the gastrointestinal tract, especially in the large intestine, and unfortunately some of those polyps can develop into colon cancer at some point in their life.
The large intestine is found in the abdominal cavity, which can be thought of as having two spaces - the intraperitoneal space and the retroperitoneal space.
The intraperitoneal space contains the first part of the duodenum, all of the small intestines, the transverse colon, sigmoid colon, and the rectum; the retroperitoneal space contains the distal duodenum, ascending colon, descending colon, and anal canal.
So the large intestines essentially weave back and forth between the intraperitoneal and retroperitoneal spaces.
Now, the walls of the gastrointestinal tract are composed of four layers.
The outermost layer is the serosa for the intraperitoneal parts, and the adventitia for the retroperitoneal parts.
Next is the muscular layer, which contracts to move food through the bowel.
After that is the submucosa, which consists of a dense layer of tissue that contains blood vessels, lymphatics, and nerves.
And finally, there’s the inner lining of the intestine called the mucosa; which surrounds the lumen of the gastrointestinal tract, and comes into direct contact with digested food.
The mucosa has invaginations called intestinal glands or colonic crypts, and it’s lined with large cells that are specialized in absorption.
In juvenile polyposis syndrome there’s an autosomal dominant mutation in the SMAD4 gene, which encodes a protein that’s part of a pathway that induces apoptosis or programmed cell death.
Without a functioning SMAD4 gene, the gastrointestinal cells that mutate are more likely to escape having to undergo apoptosis, and instead they simply divide faster than usual - ultimately giving rise to polyps, which are benign outgrowths that arise along the gastrointestinal tract, mostly in the colon.
Some polyps then go on to accumulate additional mutations in other tumor suppressor genes like the p53 gene, and at that point they might evolve into cancer.
The chance for any single polyp to develop into cancer is generally quite low, but people with juvenile polyposis syndrome have so many polyps, that they have a higher risk of cancer because the chance that a single one might turn into a cancer is significant.
In fact, many individuals with juvenile polyposis syndrome develop cancer by age 45.
Usually it’s colorectal cancer, but the SMAD4 gene is expressed in other tissues, and they sometimes develop cancers of the small intestine, stomach, and pancreas as well.
Polyps can be classified by their gross appearance.