Balkan Journal of Medical Genetics

RECURRENT INCREASED NUCHAL TRANSLUCENCY: A FIRST TRIMESTER PRESENTATION OF FAMILIAL 13p SATELLITE DELETION
Uzun I, Has R, Alici E, Ozdemir M, İnan C, Erzincan S
*Corresponding Author: Dr. Isil Uzun, Department of Obstetrics and Gynecology, Acibadem Hospital, Halit Ziya Usakhıgil Street, Bakırkoy, İstanbul, Turkey. Tel: +90-212-414-4400. Fax: +90-212-414-4152. E-mail: isiluzu@gmail.com
page: 103

DISCUSSION

Chromosome 13 is one of the acrocentric chromosomes of the human karyotype, which also include chromosomes 14, 15, 21, and 22. The acrocentric chromosomes are the most variable chromosomes in the human karyotype. There is considerable shuffling of various repetitive DNA sequences consisting of the pericentromeric, short arm and satellite regions of these chromosomes. Variations include staining and/or size of the pericentromeric regions, short arms and satellites, as well as variation in the number and/or size of nucleolar organizing regions. None of these variations appear to have any clinical consequences [1]. Nielsen et al. [2] reported two cases with 13p satellite deletions in their population study. The first case was totally normal; however, deviant behavior and criminality were observed in the second case. Studies indicate that the frequency of short arm satellites in acrocentric chromosomes in the population is between 0.5 and 1.0 per 1000 persons and that the lack of short arm satellite material does not have any deleterious effects on the phenotype [2]. In our case, 13p satellite deletions were detected in both maternal and paternal karyotypes. The couple was not related to each other in any way. To the best of our knowledge, this is the first report of a first trimester presentation of a 13p satellite deletion. The deletion is thought to be associated with enlarged NT; however, a congenital heart defect or other structural abnormalities known to cause nuchal edema was absent. Increased NT is defined as an important marker for fetal chromosomal abnormalities and is used as a routine first-trimester screening test in many countries [3,4]. Some of the cases with increased NT are linked to submicroscopic chromosomal abnormalities that are typically missed by conventional karyotyping. Approximately 12.5% of fetuses with increased NT and an apparently normal karyotype have submicroscopic chromosomal abnormalities that are likely to be pathological [5]. The risk of genetic syndromes or neurodevelopmental delays in fetuses with increased NT at the first trimester and with normal karyotype is not yet well established. A systematic review demonstrated a 4.0% [95% confidence interval (95% CI) (2.0-7.0) incremental yield for isolated NT. The most common pathogenic copy number variations reported were 22q11.2 deletion, 22q11.2 duplication, 10q26. 12q26.3 deletion and 12q21q22 deletion [6]. In this report, increased NT in both cases are probably related to 13p presentation. Perinatologists should consider 13p satellite deletions in their differential diagnoses in the event of an enlarged NT when this appears to be an isolated finding. Short arm satellites in acrocentric chromosomes as 13p satellite deletions may be a cause of increased NT. It should be noted that this is a relatively frequent phenomenon. This case demonstrates the importance of genetic counseling, karyotyping and microarray testing in the case of markedly increased NT. Non invasive prenatal testing via cell-free DNA is not adequate for increased NT. Correct diagnosis will help in the management of the present pregnancy and in counseling for future pregnancies. Declaration of Interest. The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.

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