Recurrence of neonatal haemochromatosis in half sibs born of unaffected mothers.

We report two families in which neonatal haemochromatosis was observed in half sibs. In the first family, two successive girls were born of different fathers. In the second family, an affected brother and sister were followed by an affected half brother born after donor insemination. These observations, as well as a previous abstract describing two affected half sisters, revive the debate over the inheritance of neonatal haemochromatosis. Incomplete penetrance or gonadal mosaicism for a dominant disorder, a maternal "environmental factor", or mitochondrial defect may be more suitable explanations than autosomal recessive inheritance in this condition. Alternative modes of fertilisation, such as donor insemination or in vitro fertilisation with donor eggs, should be considered with caution.