R659X mutation in the MLH1 gene in hereditary non-polyposis colorectal cancer(HNPCC) in an Indian extended family.
OBJECTIVE
Hereditary non-polyposis colorectal cancer (HNPCC or Lynch syndrome), is a genetically heterogeneous disorder that is believed to account for 2-10 per cent of all the colorectal cancer cases. The disease follows autosomal dominant inheritance pattern with high penetrance (85%) and younger age of onset when compared to patients with sporadic tumours. HNPCC is associated with germ-line mutations in the DNA mismatch repair (MMR) genes namely MLH1, MSH2, MSH6, and PMS2. The present study was aimed at analyzing mismatch repair gene(s) in an extended Indian family satisfying the Amsterdam criteria, and extending the analysis to general population to estimate frequency of the mutations/polymorphisms observed.


METHODS
A total 12 members of the HNPCC family were studied for genetic investigation. Ethnically matched 250 normal individuals were also included as controls to study the observed mutations/polymorphisms at population level.


RESULTS
The analysis resulted in identification of a 1975C>T mutation in exon 17, resulting in substitution of arginine residue with stop codon at codon 659. 655A>G substitution was also observed, resulting in replacement of isoleucine with valine at codon 219. Similar analysis on 250 ethnically matched control subjects revealed complete absence of R659X mutation, while I219V variant was found in 9.8 per cent of the controls.


CONCLUSIONS
R659X mutation correlates with disease phenotype, and 655A>G locus is highly polymorphic. Our study suggested that R659X substitution was prime cause for the disease phenotype in this family. I219V substitution is a polymorphism having no association with the disease onset or segregation. The family members harbouring this mutation were advised to be under regular medical surveillance.
Rajender
Singh
S
Division of Endocrinology, Central Drug Research Institute (CSIR), Lucknow, India.
Pooja
Singh
S
Kumar
M V Kranthi
MV
Karwasra
Rajendra
R
Singh
Lalji
L
Thangaraj
Kumarasamy
K
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics*; D000368:Aged; D020137:Base Pair Mismatch; D001483:Base Sequence; D003123:Colorectal Neoplasms, Hereditary Nonpolyposis / Q000235:genetics*; D017931:DNA Primers; D004260:DNA Repair / Q000235:genetics; D005091:Exons; D005260:Female; D006801:Humans; D007194:India; D008297:Male; D008875:Middle Aged; D000070957:MutL Protein Homolog 1; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics*; D010375:Pedigree
D048868:Adaptor Proteins, Signal Transducing; D017931:DNA Primers; C501486:MLH1 protein, human; D009687:Nuclear Proteins; D000070957:MutL Protein Homolog 1