Clinical diagnosis and genetic analysis of a foetus with mosaic karyotype comprising three cell lines and cat-eye syndrome: a case report

Cat-eye syndrome (CES), also known as Schmid–Fraccaro syndrome, is named from the characteristic iris coloboma resembling a feline eye that is present in most affected infants (1). In addition, this condition forms a classic triad with anorectal malformations and auricular abnormalities that is present in 40% of patients, and other congenital defects may also be observed. This rare chromosomal disorder, with an estimated incidence of 1:50,000 to 1:150,000 live births (2), results from partial trisomy or tetrasomy of chromosome 22pter→22q11, which typically manifest as small supernumerary marker chromosomes (sSMCs). The sSMCs is found in over 90% of individuals with this syndrome. We report the case of a full-term foetus that was followed from early pregnancy to pregnancy termination. The foetus, which presented with increased nuchal translucency(NT, 3.6 mm), was evaluated at our prenatal diagnosis clinic. Chorionic villus sampling(CVS) and amniocentesis were performed for karyotyping(G-banding) and performing single-nucleotide polymorphism microarrays(SNP-arrays), quantitative fluorescent polymerase chain reaction(QF-PCR), and prenatal colour Doppler ultrasound. The results were as follows: QF-PCR(CVS): no abnormalities detected; SNP-array(CVS): arr (22)×2–3; G-banding karyotype(amniotic fluid): mos 47,U,+22[38]/47,U,+mar[22]/46,U[44]; QF-PCR(amniotic fluid): no abnormalities detected; SNP-array(amniotic fluid): arr (22)×2–3; arr[GRCh37] 22q11.1q11.21(16888900_18631873)×2–3. Prenatal colour Doppler ultrasound(19 + 2 weeks) revealed a single umbilical artery, cerebellar vermis agenesis, and suspected renal developmental abnormalities(two renal arteries observed in one kidney). The prenatal diagnosis of CES remains challenging. The foetus with a mosaic karyotype comprising three cell lines: trisomy 22, tetrasomy 22q11.1q11.21(sSMCs), and normal karyotype, perhaps provides new evidence for a better understanding of the diagnosis of cat eye syndrome, and emphasizes the importance of genetic counseling and supervision.