The first de novo non-mosaic 14q11.2q13.1 tetrasomy of paternal origin.

Tetrasomy 14q11q13 is a very rare chromosome aberration. So far, only five patients with such an imbalance were described. All these patients had a de novo marker chromosome idic(14)(q13) leading to a partial tetrasomy of chromosome 14. We report on the first case of a de novo non-mosaic partial tetrasomy 14q resulted not from a marker chromosome, but from an inverted triplication on paternal chromosome 14, characterized by using FISH and SNP array. Our patient showed some anomalies described in tetrasomy 14q11q13 with striking presence of paternal UPD(14) features (blepharophimosis, small thorax, and joint contractures, developmental delay). This unique patient supports the hypothesis that 14q11q13 may contain imprinted gene(s) that contribute to the paternal UPD(14) features of joint contractures and/or blepharophimosis. This patient demonstrates the utility of parent of origin testing in patients with de novo chromosome 14 aberrations. Overdosage of 14q11.1q13.1 may cause some features related to UPD(14) phenotype.

Enlarged NT (≥3.5 mm) in the first trimester - not all chromosome aberrations can be detected by NIPT.

BACKGROUND: Since non-invasive prenatal testing (NIPT) in maternal blood became available, we evaluated which chromosome aberrations found in our cohort of fetuses with an enlarged NT in the first trimester of pregnancy (tested with SNP microarray) could be detected by NIPT as well. METHOD: 362 fetuses were referred for cytogenetic testing due to an enlarged NT (≥3.5 mm). Chromosome aberrations were investigated using QF-PCR, karyotyping and whole genome SNP array. RESULTS: After invasive testing a chromosomal abnormality was detected in 137/362 (38 %) fetuses. 100/362 (28 %) cases concerned trisomy 21, 18 or 13, 25/362 (7 %) an aneuploidy of sex chromosomes and 3/362 (0.8 %) triploidy. In 6/362 (1.6 %) a pathogenic structural unbalanced chromosome aberration was seen and in 3/362 (0.8 %) a susceptibility locus for neurodevelopmental disorders was found. We estimated that in 2-10 % of fetuses with enlarged NT a chromosome aberration would be missed by current NIPT approaches. CONCLUSION: Based on our cohort of fetuses with enlarged NT we may conclude that NIPT, depending on the approach, will miss chromosome aberrations in a significant percentage of pregnancies. Moreover all abnormal NIPT results require confirmatory studies with invasive testing, which will delay definitive diagnosis in ca. 30 % of patients. These figures are important for pretest counseling enabling pregnant women to make informed choices on the prenatal test. Larger cohorts of fetuses with an enlarged NT should be investigated to assess the additional diagnostic value of high resolution array testing for this indication.