Foetal megakaryoblastic abnormality associated with congenital limb amputation in the br/br rabbit

Recent research on the br/br rabbit is summarized. In all homozygous individuals, limb amputations result from in utero haemorrhages which develop in the extremities and lead to necrosis. An inner-ear abnormality is observed in about 25% of the cases. By studying a large number of gestations and birth, we observed that homozygous crossings result in about 100% amputated animals while crossings between heterozygous and homozygous rabbits result in about 50% of the young being abnormal. Observations of megakaryoblastic cells in 15- and 17-day foetal liver show a predominance of immature cells in 15-day br/br foetuses. This abnormality disappears on day 17. The possible role of megakaryoblastic cells in br/br rabbit amputation is discussed.