title: Germline RET sequence variation I852M and occult medullary thyroid cancer: harmless polymorphism or causative mutation?
abstract: OBJECTIVE
  Rearranged during transfection (RET) gene analysis, widely used to identify carriers at risk of medullary thyroid cancer (MTC), occasionally uncovers novel sequence 'variants of unknown clinical significance' including RET I852M. This study aimed to clarify whether RET I852M represents a harmless polymorphism or a pathogenic mutation.
  
  
  METHODS
  Clinical investigation supported by functional characterization of I852M mutant cells in vitro.
  
  
  METHODS
  Genotype-phenotype correlation including five kindreds from a three-generational Caucasian I852M RET family.
  
  
  RESULTS
  A node-negative occult MTC was found in the 64-year-old index patient who had increased basal and stimulated peak calcitonin levels of 190 and 13 307 ng/l, respectively. Her 4-year-old grandson had no histopathological evidence of C-cell disease although his serum calcitonin levels had increased within 5 months from 3·2 to 6·3 ng/l basally and from 17·2 to 24·5 ng/l after pentagastrin stimulation. His mother and two 11- and 1·5-year-old siblings, also carrying the gene, had normal basal and stimulated calcitonin levels and hence did not undergo surgery. Functional characterization of transfected NIH3T3 cells in vitro (cell proliferation rate; cell viability; anchorage-independent cell growth; cell migration; and invasion) indicated that I852M mutant cells have transforming and migratory activities similar to American Thyroid Association (ATA) class A V804M mutants. I852M mutants demonstrated a weaker proliferative potential than fast-proliferating ATA class C C634R mutants and revealed a weaker migratory activity compared with aggressively growing ATA class D A883F mutants.
  
  
  CONCLUSIONS
  I852M sequence variations represent genuine RET mutations, falling into ATA class A of weakly activating RET germline mutations.
authors.affiliation: Department of General, Visceral and Vascular Surgery, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany. AndreasMachens@aol.com
authors.forename: Andreas
authors.initials: A
authors.lastname: Machens
authors.forename: Alf
authors.initials: A
authors.lastname: Spitschak
authors.forename: Kerstin
authors.initials: K
authors.lastname: Lorenz
authors.forename: Brigitte M
authors.initials: BM
authors.lastname: Pützer
authors.forename: Henning
authors.initials: H
authors.lastname: Dralle
mesh_terms: D000328:Adult; D000369:Aged, 80 and over; D000818:Animals; D018278:Carcinoma, Neuroendocrine; D002648:Child; D002675:Child, Preschool; D005260:Female; D018095:Germ-Line Mutation / Q000502:physiology; D006801:Humans; D007223:Infant; D007532:Isoleucine / Q000235:genetics; D008297:Male; D008715:Methionine / Q000235:genetics; D051379:Mice; D008875:Middle Aged; D009154:Mutation / Q000502:physiology; D041681:NIH 3T3 Cells; D009382:Neoplasms, Unknown Primary / Q000235:genetics*; D010375:Pedigree; D020641:Polymorphism, Single Nucleotide / Q000502:physiology; D051096:Proto-Oncogene Proteins c-ret / Q000235:genetics*; D013964:Thyroid Neoplasms / Q000235:genetics*
chemical_list: D007532:Isoleucine; D008715:Methionine; D051096:Proto-Oncogene Proteins c-ret; C099282:RET protein, human