Table 1. Non-Hispanic white participants included in the young-onset breast cancer genotyping analysis.

Group description	Number of families	Number of people	Number of cases
Trios (affected sister, both parents)	415	1245	415
Sister-pairs (1 affected, 1 unaffected)	353	706	353
Affected sister and mother	299	598	299
Affected sister and father	22	44	22
Affected sister only	108	108	108
Affected sister, unaffected sister, father	81	243	81
Unaffected sister only	11	11	0
Mother only	2	2	0
Parents only	2	4	0
Unaffected sister and father	2	4	0
Tetrad (both sisters, both parents)	1	4	1
TOTAL	1296	2969	1279