Abstract
Presence of supernumerary marker chromosome (SMC) is a rare chromosomal abnormality with broad-spectrum of possible clinical consequences. Most carriers are healthy people, but some SMCs could be associated with infertility, especially in males.
They are also more frequent in intellectual disability and cases with various congenital defects. Genetic counselling in cases of prenatal detection of SMCs is rather challenging since prognosis differs widely depending on the SMC chromosomal origin and presence of specific segments.
Thus, every new published case is valuable for decision-making. Here, we report a case of the 33-year-old healthy woman referred to clinical geneticist as parent of the deaf child.
She was cytogenetically examined due to chromosomal aberration in the pregnancy of her mother. In her peripheral blood lymphocytes two SMCs in a mosaic form were detected by various FISH methods.
Our analysis revealed that the first SMC is derivative chromosome 7 containing Williams-Beuren region (7q11.23) which belongs to considered dosage-sensitive area of this chromosome but was clinically silent. Besides the larger SMC we also recognized a smaller SMC, where due to its low frequency and size it was impossible to determine its origin (likely from constitutive heterochromatin).
Our observations are compared with similar case reports. Supported by the GAUK-264811 and TACR-TA01010931.