A 39-year-old, gravida 2, para 1, woman underwent amniocentesis at 18 weeks of gestation because of advanced maternal age. Cytogenetic analysis of cultured amniocytes revealed mosaic supernumerary isochromosome 18p. In four of 33 separated colonies of cultured amniocytes, an abnormal karyotype of 47,XY,þi (18) (p10) was noted, while the other 29 colonies had a karyotype of 46,XY. The karyotype of cultured amniocytes at first amniocentesis was 47,XY,þi(18)(p10)[4]/46,XY[29]. Level II ultrasound

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... indings were unremarkable. She underwent repeat amniocentesis at 24 weeks of gestation, and cord blood sampling at 26 weeks of gestation. Cytogenetic analysis of cultured amniocytes revealed a karyotype of 47,XY,þi(18)(p10)[8]/46,XY[38] at the second amniocentesis. In eight of 46 separated colonies of cultured amniocytes, a karyotype of 47,XY,þi (18)(p10) was noted, while the other 38 colonies had a karyotype of 46,XY. Array comparative genomic hybridization (aCGH) on amniotic fluid using oligonucleotide array revealed a result of arr 18p11.3p11.1 (0e13,884,871) Â 2w3. Cytogenetic analysis of cord blood lymphocytes revealed a karyotype of 46,XY in 100/ 100 cells. The woman underwent a third amniocentesis at 27 weeks of gestation. Interphase fluorescence in situ hybridization (FISH) on uncultured amniocytes, using an 18p11.32-specific probe (RP11-324G2) (178,384-350,551, dye: fluorescein isothiocyanate (FITC), green) and a control 18q23-specific probe (RP11-154H12) (77,437,746e77,600,269, dye: Texas Red), showed four green signals and two red signals in 7.1% (6/84 cells) of uncultured amniocytes, and two green signals and two red in 82.9% (78/84 cells) of uncultured amniocytes (Fig. 1) . Whole-genome aCGH on the DNA extracted from the uncultured amniocytes obtained from 10 mL of amniotic fluid was performed using NimbleGen ISCA Plus Cytogenetic Array (Roche NimbleGen, Madison, WI, USA). aCGH detected a 15.31-Mb gene dosage increase at 18p11.32e18p11.21, or arr [hg 19] 18p11.32p11.21 (0e15,310,000) Â 2.13 with a log 2 ratio of 0.091 (Fig. 2) . Cytogenetic analysis of cultured amniocytes revealed a karyotype of 47,XY,þi(18)(p10)[9]/46,XY[18] at the third amniocentesis. In nine of 27 separated colonies of cultured amniocytes, a karyotype of 47,XY,þi(18)(p10) was noted (Fig. 3) , while the other 18 colonies had a karyotype of 46,XY. The woman decided to continue the pregnancy. A healthy 3450 g male baby was delivered uneventfully at term. Interphase FISH on uncultured urinary cells, using an 18p11.32-specific probe (RP11-324G2) (spectrum green) and an 18q23-specific probe (RP11-154H12) (spectrum red), showed four green signals and two red signals in 5.2% (5/97 cells) of uncultured urinary cells and two green signals and two red signals in 94.8% (92/97 cells) of uncultured urinary cells (Fig. 4) . When examined at 1 month of age, the infant was apparently normal in growth and development without any phenotypic abnormalities. Tetrasomy 18p (OMIM 614290) or isochromosome 18p syndrome is characterized by facial dysmorphism of low-set malformed ears, small pinched nose, small mouth, high-arched palate, micrognathia and prognathism, developmental delay, and cognitive impairment in most cases; neonatal feeding problems, growth Conflicts of interest: The authors have no conflicts of interest to declare.