Table 1: Historic record of JMML (previously named JCML or jCMML) twin cases.

JMML/JCML/(j)CMML MZ type	Karyotype Twin_01	Karyotype Twin_02	Reference	Comments
(j)MML+ monochorionic	46,XY	46,XY; at final stage of the disease Ph+	Arch. of disease in childhood, 1977, 52: 72-74	Both twins deceased after a similar course of the disease
(j)MML	No Karyotypic marker	No Karyotypic marker	Cancer, 1984, 54: 675-686	Twin sister disease after a different course of disease
JMML No data monozygotic type	46,XX	46,XX	Cancer Genet Cytogenet 1989, 38: 205-213	Karyotypes of both twins evolved with hyperdiploid clones; Both twins deceased after a similar course of the disease
JCML Monozygosity 98%	46,XY, -7, +mar	46,XY, -7, +mar	Leukemia 1997, 11: 306-312	Both twins responded well to therapy
CMML ND monozygotic type	46,XY, t(7;16)(p10;q10)*	46,XY, t(7;16)(p10;q10	BLOOD, 1995, 85: 1742-1750	Twin_01 deceased at 5 month after diagnosis Twin_02 is alive at 11 month after diagnosis**
JCML ND on twin type	ND	ND	BJH, 1995.90: 353-357	In one twin B-lineage clonality was demonstrated
JMML monochorionic- biamniotic	46,XX with NRAS mutation	Free of disease	Pediatric Blood Cancer 2008, 50: 665-667	Discordant JMML in two twins

+This twin pair was included here since the Ph+ karyotype was found only in the terminal phase of the disease and because it is the 'oldest' case reporting a twin pair with a myelomonocytic leukemia. *constitutional translocation also present in the father without hematologic abnormalities; ** alive at time of publication (1995);