Table 4.

Molecular basis of low penetrance retinoblastoma

Type of mutation	Number of LP families	Description of mutations and frequency a	Functional consequences
Regulatory	3	-198G>A (1/2) -188G>T (1/2) -149G>C (1/1)	Low expression of normal Rb protein
MS point mutations	12	R661W (8/20) C712R (2/5) W563L (1/1) R787Q (1/1)	Partial inactivation of Rb protein
Inframe deletion	3	Del:N480 (1/1) Del:E04 Del: E24–25	Partial inactivation of Rb protein
Splicing	10	607+1G>T (4/11) 862-10T>C (1/1) 539+1delG, del E05 (1/1) 2325+5G>A, del E:22 (1/1) Q443P/del:E13 (1/1) V654L/splice (1/2) E732E/del E:21(1/2)	Alternative splicing and/or unessential exon skipping resulting in low expression or partial inactivation of Rb protein
NS point mutation	1	Q675X (1/1)	Alternative splicing involving the stop codon

^aRatio of mutations found in LP families vs. all mutations in the database is shown in brackets