|Year : 1975 | Volume
| Issue : 3 | Page : 23-25
Cytogenetics in retinoblastomas
K Srinivasa Rao, C Ramakrishna Rao, G Radhakrishna
Andhra Medical College, Visakhapatnam, India
K Srinivasa Rao
Additional professor of Pathology, Andhra Medical College, Visakhapatnam
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Rao K S, Rao C R, Radhakrishna G. Cytogenetics in retinoblastomas. Indian J Ophthalmol 1975;23:23-5
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.  reported a deleted No. 14, Gey  reported a deleted No. 13 and Grace and coworkers  described a ring 13. Recently Orye et al.  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|| |
Chromosome analysis was done by the modified method of Moorehead.  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,  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|| |
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|| |
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 ,, . 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  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. 
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|| |
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.
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[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4]