Table 2 Percentage of spontaneous and diepoxybutane (DEB) induced chromosome breakage in patient and control cell lines.

	Cases	Per cent of breaks per cell
		Spontaneous	DEB
Test 1	III‐1	0.18	0.56
	Normal control	0.04	0.16
Test 2	III‐1	0.11	0.54
	Normal control	0.02	0.04
	Control range*	(0.00 to 0.14)	(0.00 to 0.20)
	Affected range*	(0.18 to 0.48)	(0.44 to 1.25)

*The quoted ranges for control and Fanconi anaemia cells are those established by the cytogenetics laboratory at Guy's Hospital.