Interesting topic, Marc...
I've been accused that my posts are too long, so I'll try to keep this brief
Maybe the defect is purely a physical one and not genetic at all, possibly due to womb position? Who knows, maybe the fetus / baby gets all twisted up in there and the veins don't develop properly????
My 2nd child was born breach (it was a real bitch flipping his butt around).. Hopefully, he doesn't have any malformed veins !
I know we all want to get better, but if we can prevent MS from occurring in the first place would be huge...
From Wikipedia, the free encyclopedia
Certain factors can encourage a breech presentation. Prematurity is likely the chief cause. Twenty five percent of fetuses are in the breech position at 32 weeks gestation; this drops to three percent at term. The increasing size of the fetus near term traps the fetus into the head down position normally. Pregnancies ending in preterm birth simply recruit more breeches before they can turn to head down. Factors predisposing to term breech presentation include:
multiple (or multifetal) pregnancy (twins, triplets or more)
abnormal volume of amniotic fluid: both polyhydramnios and oligohydramnios
fetal anomalies: hydrocephaly, anencephaly and other congenital abnormalities
prior Cesarean section
It is postulated that the baby normally assumes a head down presentation because of the weight of the baby's head. As the mass of the fetal head is the same as that of the pelvis, it is more likely that the enlarging fetus is more and more restricted in its movements, and simply becomes entrapped. The shape of the uterus is a more likely determinant of the final fetal presentation as uterine shape anomalies are strong predictors of breech presentation and other malpresentations.
Congenital disorder involves defects in or damage to a developing fetus. It may be the result of genetic abnormalities, the intrauterine (uterus) environment, errors of morphogenesis, or a chromosomal abnormality. The outcome of the disorder will further depend on complex interactions between the pre-natal deficit and the post-natal environment. Congenital disorders vary widely in causation and abnormalities. Any substance that causes birth defects is known as a teratogen. The older term congenital  disorder does not necessarily refer to a genetic disorder despite the similarity of the words.