Antenatal diagnosis of mixoploidy: a case report

Abstract

Diploid triploid mosaicism, or mixoploidy is a rare perinatal diagnosis. It is characterized by multiple congenital anomalies including mental and growth retardation, facial and body asymmetry, malformed or low set ears, 3-4 finger syndactyly, and ambiguous genitalia (in males). Areas of hyper- and hypo-pigmentation have also been described. The more severe brain, renal, cardiac and ocular anomalies associated with complete triploidy are not apparent in mixoploid individuals. We present a case of antenatal diagnosis by FISH analysis. The index case was a 26yo G2P1 female referred for ultrasound evaluation at 36 weeks secondary to an abnormal aortic arch. Ultrasound findings included echogenic bowel and significant growth deceleration. A 6-week abdominal growth lag was apparent. A review of the patient's records indicated that growth retardation was evident as early as 26 weeks. An amniocentesis was performed for chromosome analysis and lung maturity. Lung maturity was confirmed. FISH was performed for chromosomes 13, 18 and 21 in addition to routine karyotyping. Out of 179 cells, 36 showed 3 signals for chromosome 18. Out of 104 cells, 19 showed 3 signals each for chromosome 13 and 21. Mixoploidy was confirmed by standard karyotype techniques 1 week later. The mother was delivered within 24 hours of receiving the FISH results. Growth retardation, low set ears and 3-4 finger syndactyly were all present at birth. Cord blood and peripheral blood analysis confirmed the diagnosis of mixoploidy. The findings “disappeared” on peripheral blood by 8 wks. Growth restriction has long been recognized as a feature of chromosome abnormalities. We propose that persistent growth asymmetry be considered part of this sequence as well. Review of the prenatal findings of other affected children may help delinete the prenatal phenotype further. The disappearance of the mosaic cell line in the blood makes the prenatal setting the optimal choice.