Triple-X Syndrome in a Trisomic Down Syndrome Child: Both Aneuploidies Originated from the Mother

Here we report a case of double aneuploidy showing trisomy 21 and triple-X chromosome in a case of Down syndrome born to young non-consanguineous parents. The child presented with strabismus, periorbital swelling, scanty eyebrows and microganthia in addition to Down features. Molecular characterization has shown the maternal origin of double aneuploidy with trisomy 21 at meiosis-II and triple-X at meiosis-I. *Address for Correspondence: Institute of Human Genetics, FRIGE House, Jodhpur Gam Rd, Satellite, Ahmedabad 380 015, Gujarat, India INTRODUCTION Aneuploidy is the second most important category of chromosome mutations relating to abnormal chromosome number. Trisomy 21 and numerical sex chromosome anomalies are common chromosomal disorders, with a birth incidence of 1:700 to 1:2,500 respectively (Kovaleva and Mutton 2005). The chances of two chromosomal anomalies occurring in a single conceptus are a rare event and the reported incidence varies from 0.21% to 2.8% in spontaneous miscarriages subjected to cytogenetic study (Guzel et al. 2009). Nonetheless, the incidences might be more than the expected occurrence if multiplied by the individual frequencies of each aneuploidy (Hook 1992). However, the underlying mechanism involved in the formation of double aneuploidy (DA) is not well understood. Parental origin is studied only in a small number of cases and both non disjunctions occurring in a single parent is an extremely rare event. Because of the rarity and for an addition to the existing literature, we present a case of double aneuploidy in a clinically suspected case of Down syndrome.