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Know your genes- BRCA, MEN, APC, HNPCC

Author:Lengyel J.
on 01 Jun, 2007

Last edited by: Lengyel J. on 12 Oct, 2007
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Know your genes
 
BRCA1
BRCA1 s a human gene that belongs to a class of genes known as tumor suppressors.
 
The BRCA1 gene is located on the long (q) arm of chromosome 17 at position 21
 
Associations
BRCA1 gene also increase the risk on ovarian, Fallopian tube, prostate and colon cancers.
 
 
 
BRCA2
The BRCA2 gene is located on the long (q) arm of chromosome 13 at position 12.3
 
Associations
Ovary, prostate, pancreatic
People who have two mutated copies of the BRCA2 gene have one type of Fanconi anemia.
 
 
 
APC Gene (Familial adenomatous polyposis (FAP))
APC (adenomatosis polyposis coli) is a human gene that is classified as a tumor suppressor gene.
The APC gene is located on the long (q) arm of chromosome 5 between positions 21 and 22
 
When this condition results from mutations in the APC gene, it is inherited in an autosomal dominant but also can be inherited as autosomal recessive.
The relationship of the mutation wihtin the APC gene governs it's phenotypic expression.
 
  • Thus a mutation before exon 9 produces ab attenuated form of the disease whihc presents 40-50yrs.
  • APC mutations between exon 9 and codon 1444 of exon 15 are usually associated with bilateral Congenital Hypertrophy of the Retinal Pigment Epithelium (CHRPE).

 http://www.mrcophth.com/retinacases/rpehypertrophyh.html

  • Mutations in exon 15 typically lead to the development of hundreds to thousands of colonic polyps
 
Common mutation in familial adenomatous polyposis is a deletion of five bases (the building blocks of DNA) in the APC gene.
 
Hereditary nonpolyposis colorectal cancer (HNPCC),
 
Aso known as Lynch syndrome, The increased risk for cancer is due to inherited mutations that degrade the self-repair capability of DNA. So called mismatch repair genes. Over 800 muytations. Commonest 2 are
The human mutL homologue hMLH1 is located at chromosome 3p21
hMSH2 is gene is located at chromosome 2p21.  AD inheritance.
 
 
 
 
 
Associations
Risk of colorectal cancer (80%)and other cancers such as endometrium(80%), ovary, stomach, small intestine, hepatobiliary tract, upper urinary tract, brain, and skin. HNPCC is subdivided into Lynch Syndrome I (familial colon cancer) and Lynch Syndrome II (HNPCC associated with other cancer of the gastrointestinal system or the reproductive system).
 
Medscape article on
 
MEN
            Autosomal dominant inheritance
 
MEN 1 (gene at 11q13)
Pancreas 80% non functional – pancreatic polypeptideoma
                  40% gastrinoma-[20% patients with gastrinoma have MEN1]
                              Zollinger-Ellision syndrome (PUD , diarrhoea)
                              Dx – gastrin levels
                  10% insulinoma                                                                    
Pituitary (anterior) Prolactinoma
Parathyroid (Primary hyper parathyroidism 90%)
Foregut carcinoids
MEN 2a (caused by mutation in the RET gene Chromosome 10)
Medullary thyroid
Phaeo
Hyperparathyroidism
 
MEN2b
Medullary thyroid
Phaeo
Marfanoid etc
 
 
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