Abstract
Robertsonian translocations (RT) are among the most common balanced structural rearrangements in humans and comprise complete chromatin fusion of the long arm of two acrocentric chromosomes. Nevertheless, non-Robertsonian translocation involving these chromosomes is a rare event. We report a de novo unbalanced translocation involving chromosomes 15 and 21. The newborn was the daughter of a 29-year-old mother and a 42-year-old father. The couple was non-consanguineous. Clinical findings led to the diagnosis of Down syndrome (DS) with severe congenital heart defects (persistent arterial duct, and complete atrioventricular septal defect), as well as low birth length and weight (< 5th and < 10th percentile, respectively, based on specific measurement curves for DS). Conventional cytogenetic analysis revealed the karyotype 46,XX,der(15)(15pter → 15q26.2::21q11.2 → 21 qter). The translocation was confirmed by means of fluorescence in situ hybridization. The parents had normal karyotypes. Differently from RT, in our case a rare event occurred involving the distal segment of 15q and the proximal segment of 21q. Only two reports of this translocation, involving chromosomes 15 and 21 but different breakpoints, have been described so far. The association between 21q duplication and 15q deletion makes it difficult to separate the effect of each chromosome, but might also be responsible for increasing the growth retardation, as detected in our case. Cytogenetic analysis on DS patients is mandatory not only to confirm the diagnosis, but also to assess the risk of recurrence at genetic counseling, as well as to evaluate the contribution of other chromosome aberrations in the final phenotype.
Highlights
INTRODUCTIONThe majority (approximately 95%) of Down syndrome cases are caused by simple trisomy of chromosome 21
The majority of Down syndrome cases are caused by simple trisomy of chromosome 21
CASE REPORT: We report a de novo unbalanced translocation involving chromosomes 15 and 21
Summary
The majority (approximately 95%) of Down syndrome cases are caused by simple trisomy of chromosome 21. The main aim of this study was to report a very rare de novo non-Robertsonian translocation involving chromosomes 15 and 21, and to show the importance of cytogenetic investigation in all cases of clinical diagnosis of Down syndrome. CASE REPORT A female newborn was referred to the Genetic Counseling Service of Universidade Estadual Paulista (Unesp), Botucatu, São Paulo, with a clinical diagnosis of Down syndrome. She was the only child of non-consanguineous parents. Ultrasound examination during pregnancy detected the presence of oligohydramnios, but no renal malformations She was born at term by means of vaginal delivery with a birth length of 41 cm (< 5th percentile), weight of 2000 g (< 10th percentile) and head circumference of 33 cm (50th percentile, all measurement based on a standard chart for Down syndrome).[6]. It was impossible to have more information about this case and to collect more blood samples
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