Cutaneous neonatal lupus erythematosus: discordant expression in identical twins.

Background, Neonatal lupus erythematosus is a rare syndrome characterized essentially by cutaneous lesions and/or congenital heart block occurring in infants at birth, or shortly after. It is related to transplacental crossing of maternal auto antibodies (usually anti Ro/SS-A, La/SS-B or rarely anti-U,RNP) from the mother to the infant. Mothers of affected children have signs of systemic lupus erythematosus or other collagenosis or are asymptomatic. Case report. We report a case of neonatal lupus erythematosus in one identical twin, revealed at the age of 3 months by erythematous and annular cutaneous lesions of the face and limbs. These lesions were preceded at birth by an asymmetrical livedo pattern of the lower limbs. Her twin sister was unaffected but both infants had a high rate of anti-Ro/SSA antibodies. The diagnosis of neonatal lupus erythematosus permitted to reveal a biological lupus syndrome in their asymptomatic mother. Cutaneous lesions cleared almost completely within 1 year whereas antiRo/SSA antibodies disappeared. Conclusion. Cases of neonatal lupus erythematosus in twins are rare and mostly described in heterozygotic twins. Clinical discordance is usual and could partly be explained by genetic factors. In monozygotic twins, like in our case, chromosome X inactivation could be an explanation of the differences observed.