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A child with rectal bleeding is found to have multiple juvenile polyps throughout the colon. A family history of colon cancer and possible HHT features are noted.
AD
- SMAD4 (20%) - overlap with HHT (JP-HHT)
- BMPR1A (20%)
- ~40-50% no identified variant
- Juvenile (hamartomatous) polyps
- GI bleeding, anemia, protein-losing enteropathy
- CRC risk: 39-68%
- SMAD4: HHT overlap (AVMs)
- Clinical diagnosis with any one of: more than 5 juvenile polyps of the colorectum, juvenile polyps throughout the GI tract, or any number of juvenile polyps with a positive family history
- Histology shows hamartomatous polyps with abundant edematous lamina propria and cystically dilated, mucus-filled glands, distinguishing them from adenomas
- Confirm with germline SMAD4 or BMPR1A testing; about 40-50% of clinically diagnosed individuals have no identifiable variant
- Identify SMAD4 carriers specifically, since they require screening for the overlapping hereditary hemorrhagic telangiectasia phenotype (AVMs)
- Surveillance colonoscopy and upper endoscopy beginning around age 12 to 15 (or earlier if symptomatic), repeated at intervals based on polyp burden; colectomy or gastrectomy is considered when polyps are too numerous to manage endoscopically
- Monitor for and treat GI bleeding, iron-deficiency anemia, and protein-losing enteropathy
- SMAD4 carriers undergo HHT evaluation, including screening for pulmonary and cerebral AVMs
- Predictive germline testing and counseling for at-risk relatives
"SMeAr 4 presents at age 4": SMAD4 variants present in young children with rectal bleeding due to large polyps. BuMPs in Rectum/Rumen (stomach) 1n Adolescence for BMPR1A.
SMAD4 causes 3 disorders, all AD: S looks like a blood vessel (HHT), M is for Myhre syndrome (GOF variant), D4 = "Don't Force it out" (pooping, juvenile polyposis). Patients with SMAD4 have polyps + HHT (telangiectasias), while patients with BMPR1A have polyps only.