Gene for retinoblastoma is found on which chromosome

(A) (13) (300- Khurana 5th)* Retinoblastoma appears to result from loss or inactivation of both normal alleles of the retinoblastoma gene (a DNA sequence located on long arm chromosome 13, the q 14 region)* It is the most common primary intraocular malignancy of childhood (Remember MC orbital malignancy of childhood is Rhabdomyosarcoma)* Knudson's proposed ''two- hit *' hypothesis of oncogenesis for Retinoblastoma Retinoblastoma | ||Heritable (germine)Non Heritable (somatic)* 40% tumours* Bilateral multifocal tumours* Predisposition ot second non ocular cancersPineloblastoma** osteosarcoma**** 60% tumours* Unilateral* Presence of leukoria (white pupillary reflex) and calcification within the globe in a one and half year old child is almost diagnostic of retinoblastoma* Most common presentation of Retinoblastoma is leukocorea or amauratic cat *s eye reflex and strabismus *** Other presentations(i) Secondary glaucoma(ii) Red eye(iii) Buphthalmos & proptosis(iv) Orbital cellulitis(v) Painful red eye usually associated with pseudohypopyon and (hyphaema( picture stimulating iridocyclitis)(vi) Excessive tearing(vii) Corneal clouding due to elevated IOP(viii) Discolouration of iris due to neovascularization of iris* LDH Is grossly increased in Retinoblastoma (where the aqueous (plasma ratio of LDH is greater than 1.5)* Ultrasound & CT scan are able to detect a intraocular mass with calcification, which is pathognomic of retinoblastoma.* MRI is not able to detect the calcification as wall as CT but it is investigation of choice to study the optic nerve & sellar and parasellar regions of the brain.* The most common method of spread of retinoblastoma is by direct invasion of optic nerve with extension in to theCNS, Hematogenous spread may lead to distant metastasis throughout the body.* Rosettes are characteristic in retinoblastoma