Transmission ofa ringchromosome 18froma motherwith46,XX/47,XX, +r(18) mosaicism to herdaughter, resulting ina 46,XX,r( 18)

A 6montholdpatient isreported witha ringchromosome18confirmed bycytogenetic studies andinsituhybridisation. Her clinical features were similarto previous cases ofringchromosome18 syndrome.The ringchromosomewas inherited fromthephenotypically and mentallynormal motherwitha mos 46,XX/47,XX, +r(18) karyotype. (JMedGenet1993;30:964-5) The phenotypic and clinical features of patients witharingchromosome 18syndrome probably depend on theextentofdeletion of theshort or long arm andon rearrangements leading toloss or duplication ofchromosome 18sequences.' Transmission ofringchromosome 18hasrarely beenreported.'2 Inthese families one normalchromosome18 is generally replaced bythering chromosome 18. Inour study we describe a woman withpartial trisomy 18mosaicism caused byan additional ringchromosome18, resulting in a 46,XX,r(18) karyotype inherdaughter.