no. that is not a definitive sign. although a single transverse crease does appear with down syndrome it is not the only sign of this genetic disorder nor does it mean that you are prone to have a child with down syndrome.
i have the single transverse palmar crease on one hand does that mean i carry the downsyndrome gene even if i am not ds. also does having this crease mean if i get pregnant my baby will be at risk of having down syndrome? i do not have down syndrome and there is no history of it in my family but i have the crease and wondering if it will mean those questions i just asked.