RB1

This gene is located on the long arm of chromosome 13. It is a tumour suppressor gene (1).

• the RB1 gene encompasses more than 200 kilobases of genomic DNA and is composed of 27 exons
• the gene product of RB1 (pRB) plays a role in regulating cellular DNA synthesis.

Tumour growth in both heritable and non-heritable retinoblastomas is caused by biallelic mutations of the RB1 gene (2).

• in heritable disease
  • the first mutation (M1) in the RB1 gene is constitutional which predisposes the child to retinal tumours
  • the second mutation (M2) is a somatic mutation which initiates tumour growth in one or more retinal cells (2)
• in non-heritable disease
  • both the mutations are somatic events (3)

RB1 is important in the regulation of cellular proliferation in many cell lines, not just retinoblasts. Hence in constitutional RB1 mutations, there is an increased risk of secondary malignancies in the lungs, bladder, bone, soft tissues, skin and brain throughout life (2).

Reference:

• (1) Melamud A, Palekar R, Singh A. Retinoblastoma. Am Fam Physician. 2006;73(6):1039-44.
• (2) Dimaras H et al. Retinoblastoma. Lancet. 2012;379(9824):1436-46
• (3) Chintagumpala M et al. Retinoblastoma: review of current management. Oncologist. 2007;12(10):1237-46