[lemma="13q14"] [!(□=□ | □)]
[lemma="13q14"] [!(tag=□ | □)]
[lemma="13q14"] [!(lemma=□ | □)]
Analysis of the development of homozygosity for region 13q14 in sporadic tumours subsequently confirmed that probably all RB tumors are due to mutations in a single gene , RB1 . The first step , inherited predisposition , is best described for retinoblastoma in which a recessive mutation of a locus residing in the 13q14 region of the genome is unmasked by aberrant , but specific , mitotic chromosomal segregation . Further studies are needed to understand the correlative role of specific chromosome rearrangements , gene ( s ) amplification and action of recessive rb gene , located at 13q14 in initiation and progression of retinoblastoma . The most frequently observed abnormalities are losses of chromosomal material , with deletions in band 13q14 being the most common , followed by deletions in 11q22-q23 , deletions in 17p13 and deletions in 6q21 . The starting point is production of microsatellite markers from cosmids already mapped to the 13q14 region . In contrast with the cases of isolated 13q14 changes , only seven of 17 cases with 13q14 as part of complex abnormalities had typical morphology ( P = .012 ) . Deletions of the 13q14 region are found in 50 per cent of cases of B-cell chronic lymphocytic leukaemia . Using fluorescence in situ hybridisation these cosmids were all shown to hybridise to the 13q14 region but not to chromosomes known to carry subband deletions involving the RB1 gene . Ten rearrangements involving 13q14 were observed in a series of 105 retinoblastoma patients including : five de novo deletions , one of them with suspected mosaicism ; one de novo apparently balanced translocation ; four deletions due to three familial insertions .