Down syndrome caused by 21; 21 robertsonian translocation

Down syndrome, also known as Trisomy-21, is the most common viable aneuploidy in humans. It was first described as a syndrome by John Langdon Down in 1866 and later Jerome Lejeune and Patricia Jacobs explained the association between the third copy of the 21st chromosome and syndromic manifestations. The usual incidence of Down syndrome is 1 in 700 live births. Of all cases of Down syndrome, 95% are caused by non-disjunction. Robertsonian translocation of 21; 21 is extremely rare. To the best of our knowledge, we are reporting the first case of 21;21 translocation causing Down syndrome from Sri Lanka.