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|Title: ||Screening for RB1 Gene Alleles in Saudi Retinoblastoma Patients|
|Authors: ||AlMitib, Layla Hussein|
Warsy, Prof. Arjumand Sultan
|Keywords: ||RB1 Gene Alleles|
Saudi Retinoblastoma Patients
|Issue Date: ||15-Jun-2011 |
|Abstract: ||Retinoblastoma (Rb) is the most common intraocular tumor which
occurs in infantile retina and may result from germ-line or somatic mutation.
In Saudi Arabia, Rb is diagnosed at an incidence of approximately 25
cases every year. However, there is no information on the nature of mutations
in the RB1 gene.
The major aim of this study was to identify germ line mutations in the
RB1 gene in Saudi Rb patients by sequencing the entire RB1 gene. The study
was conducted on 20 Rb patients and 20 normal healthy controls. In addition,
7 affected tissue and normal tissue samples were obtained from the same
patients. The demographic data of each patient and control were recorded.
Blood was used to extract DNA, and following polymerase chain reaction, the
27 exons of the RB1 gene were sequenced. Multiplex Ligation-dependent
Probe Amplification (MLPA) studies were carried out to search for long
deletions in the patients and control.
Mutations were identified in 11/20 (55%) of the patients in the germ line
and somatic cell DNA. In the germ line DNA the mutations identified were in
exons 3, 4, 5, 18 and 19. These included small deletions resulting in
frameshift (in exon 3: c.373delG; in exon 4: c.409delG; in exon 5: 504-
505delAT), base substitutions resulting in nonsense mutation and producing
premature termination (in exon 18: c.1735C>T, p.R579X), and a point
mutation resulting in substitution of an amino acid (c.1862G>A, p.R621H). A
silent mutation was also identified (c.1917G>A). Five patients had large
deletions. One of these has deletion of exons 6-9 and four patients had exon
24-26 deletions. The patients in whom RB1 mutation was not identified may
be having a large deletion which could not be identified during sequencing.
In the somatic cell DNA (from the tissue), the mutations identified were
nonsense mutations resulting in premature termination (in exon 8: c.751C>T,
p.R251X and in exon 14: c.1363C>T, p.R455X) small deletions (in exon 5:
504-505delAT); and a large deletion of exons 24-26. A silent mutation was
also identified in the normal tissue. Of these mutations four were novel
mutations and further studies are necessary to identify their effect on the
functional aspects of the resultant Rb protein (pRb).
In the intronic regions sequenced, ten single nucleotide polymorphisms
(SNPs) were identified. These were in the introns 1, 2, 3, 4, 25 and 26. Two of
the SNPs associated significantly with retinoblastoma. rs2252544 in intron 1,
showed a statistically significant difference in the genotype frequency in the
Rb patients and controls (p<0.05), while rs1981434 also in the intron 1
showed a highly significant (p<0.0001) difference in both the genotype and
In conclusion, sequencing was considered as an effective though expensive
method for screening. It is suggested that there is a need to develop such
screening methods that will identify the mutation without screening the entire
gene in each Rb patient. Further studies are warranted to have a more clear
view of RB1 mutations involved in Rb development in Saudis.|
|Appears in Collections:||College of Science|
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