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Year : 1975  |  Volume : 23  |  Issue : 3  |  Page : 23-25

Cytogenetics in retinoblastomas

Andhra Medical College, Visakhapatnam, India

Correspondence Address:
K Srinivasa Rao
Additional professor of Pathology, Andhra Medical College, Visakhapatnam
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Source of Support: None, Conflict of Interest: None

PMID: 1236311

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How to cite this article:
Rao K S, Rao C R, Radhakrishna G. Cytogenetics in retinoblastomas. Indian J Ophthalmol 1975;23:23-5

How to cite this URL:
Rao K S, Rao C R, Radhakrishna G. Cytogenetics in retinoblastomas. Indian J Ophthalmol [serial online] 1975 [cited 2021 Jun 19];23:23-5. Available from: https://www.ijo.in/text.asp?1975/23/3/23/31313

Retinoblastoma is a malignant tumour of childhood and is congenital. From statistical study of the incidence of retinoblastoma it would appear either genetically determined, or by somatic mutation. The occurrence of genetically determined cases of retinoblastoma can be explained by the incomplete penetrance of a single, rare and autosomal dominant gene.

A number of workers in the recent times have brought to light the chromosomal anoma­lies in retinoblastomas.

Retinoblastoma has been found in 8 patients who had a karyotype showing a partial deletion of a longarm of ring formation of a D-Group chromosome. In four of these the abnormal D-chromosome was specifically identified. On the basis of auto radiography, Wilson et al. [4] reported a deleted No. 14, Gey [6] reported a deleted No. 13 and Grace and coworkers [7] described a ring 13. Recently Orye et al. [8] reported a patient with retinoblastoma who had a deleted No. 13 chromosome identified by both autoradiography and Giemsa banding pattern.

We had the opportunity to examine cyto­genetics studies in 8 cases of retinoblastomas.

Seven cases were of unilateral retinoblastomas, and one of bilateral retinoblastoma. Giemsa banding patterns also were studied and in 2 cases we had Dq-deletion syndrome, 3 cases normal, and one case A l upper arm breaks and the 8th case with bilateral retinoblastoma showed Triploidy (69-chromosomes).

  Materials and Methods Top

Chromosome analysis was done by the modified method of Moorehead. [11] A small amount of 0.5 c.c. of heparinised whole blood was innoculated into 5 c.c.pre pared tissue culture medium. This was incubated at 37`C for 72 hours. At 70th hour colchicine 0.5 c.c. was added to the prepared tissue culture medium. Harvesting of cultures and preparations of slides was done according to standard procedures. In general 11 emtaphases were analysed in every case. Karyotyping was done accord­ing to Denver typing. We used a modification of the trypsin and Giemsa banding technique of Seabright, [10] in which air dried slides are exposed to trypsin solution rinsed in buffer, stained with Giernsa and examinded. We found treatment with 0.125% trypsin for 20 seconds results in well defined banding patterns.

  Observations Top

Eleven metaphase cells of 2 cases [Figure - 2],[Figure - 3] showed 13 long arm deletion as could be seen from the karyotype analysis. One case showed A 1 upper arm breaks, and one showed triploidytotal 69 chromosomes in 20 of the cells counted. [Figure - 2],[Figure - 4]. Though Giemsa banding showed the 13 long arm deletion as seen by the banding patterns, they could not be photographed well and their relationship could not be demonstrated by the density curves of the Giemsa banding patterns due to lack of sophisticated equipment; as these tracings have to be obtained by scanning photographic prints of the chromosomes in a Beckman Densito­meter (Microzone). The ordinary photomicro­graph of the karyotype is shown in [Figure - 2].

  Discussion Top

The deleted chromosome has row been identified as No. 13 in all reported cases of retinoblastomas and Dq-in which the abnormal chromosome was specifically identified [4],[6],[8] . A genetic component involved in the normal development of the eye is apparently located on the long arm of No. 13 chromosome.

To date more than 40 individuals with a partial deletion most likely No. 13 have been described (1-8, 14-18), Distinctive somatic abnormalities of aplastic or hypoplastic thumbs has been seen in about one quarter of the reported cases. More frequently found soma­tic abnormalities are microcephaly, trigonence­phaly, protruding upper teeth, low set ears, cleft or high arched palate, micrognathia and retarded growth and development. The synd­rome is highly variable and many have been minimally affected. Mental retardation has been the consistent finding. But in our cases none of these somatic abnormalities were found and only in one case there was mental retarda­tion.

The pedigree studies in all these 8 sporadic cases showed 7 with unilateral retinoblastoma with somatic mutation type with no other siblings being involved and with no vertical or horizontal transmission. This type is not transmitted as reported by Smith and Sorsby [12] and one case arising as a germinal mutation type with dominant gene transmission noted in the great grand parent, parent and in the two siblings. The majority of these cases are bila­teral and prognosis is bad. [11]

It needs to be stressed that in sporadic uni­lateral retinoblastomas, it is essential to probe deeply in the family history for the rare irre­gular dominance with its serious complications which can easily be overlooked. Except for a small group it is fairly easy to distinguish the non-hereditary from the hereditary cases. In counselling two distinct issues arise-recognition of dominant inheritance and the problems pre­sented by sporadic unilateral retinoblastomas.

  Summary Top

A deletion of long arm of chromosome 13 results in fairly definite syndrome that seems to be associated with a high incidence of retino­blastomas. Of the 8 cases of retinoblastomas analysed by cytogenetics and karyotype analy­sis, 2 cases showed 13q-deletion syndrome, 1 case with A, upper arm breaks and 1 case with triploidy. The other 3 showed normal karyo­types. The genetics of sporadic cases of uni­lateral and bilateral retinoblastomas are dis­cussed.

  References Top

Lele, K.P., Penrose, L.D. and Stallard, H.B. 1963. Ann. Hum. Genet., 27, 171-174,  Back to cited text no. 1
Thompson, St. and Lyons, R.B., 1965. Hum. Chromosome, News letter,. 15, 21,  Back to cited text no. 2
Van Kempern, C. 1966 Maandsehrkinder geneask. 34, 92-95,  Back to cited text no. 3
Wilson, M.G., Melnyk J. and Towner J.W. 1969. Jour Med. Genet. 6, 322-323,  Back to cited text no. 4
Taylor, A.I., Human Genetik. 10, 362-365, 1970.   Back to cited text no. 5
Gey, W., 1970 Human Genetik, 10, 362-365,   Back to cited text no. 6
Grace, E,, Drennam, J., Clover, D., 1971. J. Med. Genetik 8, 351-357,  Back to cited text no. 7
Orye, E. Delebeke, M.J. and Vandenabelle, 1971 Lancet. 2, 1376.  Back to cited text no. 8
Wilsom, W.G. Joseph, W., Towner, and fu Jimoto. 1973 D-chromosome deletions. Jour. Of Hum. Genet. 25, 57-61,  Back to cited text no. 9
Seabright, M. 1971. Lancet 2, 971-972,  Back to cited text no. 10
Moorehead, P.S. 1960. Expt. Cell Res. 20, 613,  Back to cited text no. 11
Smith & Soresby 1958 Annals. Hum. GENET, 23, 50.  Back to cited text no. 12


  [Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4]


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