Karaman Birsen, Aytan Melike, Yilmaz Kader, Toksoy Guven, Onal Ebru Perim, Ghanbari Asadollah, Engur Ayse, Kayserili Hulya, Yuksel-Apak Memnune, Basaran Seher
Istanbul University, Institute of Child Health, Division of Medical Genetics, Istanbul, Turkey.
Eur J Med Genet. 2006 May-Jun;49(3):207-14. doi: 10.1016/j.ejmg.2005.06.002. Epub 2005 Jul 12.
Small supernumerary marker chromosomes (sSMCs) are often associated with developmental abnormalities and malformations are de novo in approximately 60% of the cases. Fluorescence in situ hybridization (FISH) techniques using various probes provided the possibility to analyze and characterize sSMCs, which is highly important for prenatal diagnosis and genetic counseling. We now present the establishment of a specific strategy to identify the origin and structure of the sSMCs using a combination of conventional banding and classical FISH techniques. Based on this strategy, in a series of 15,792 prenatal karyotypes, 20 cases with sSMCs (prevalence 1.26 per 1000) were diagnosed. Eighteen of these cases were completely analyzed by FISH using commercial probes and Chromoprobe Multiprobe-I System. Out of 20 sSMCs 12 were satellited (10 bisatellited and two monosatellited) (60%) and eight were non-satellited (six ring-like and two isochromosomes) (40%). sSMCs were mostly derived from chromosome 15 (10/20) (50%). Euchromatin material was found in 13 cases by various banding and FISH techniques, while in six of 20 sSMCs there was no evidence of euchromatin material. Parental karyotypes could be evaluated in 15 cases and familial inheritance was found in only three of them (20%). We conclude that the proposed strategy for the identification and characterization of sSMCs is accurate and represents a good alternative to novel FISH techniques for modestly equipped cytogenetic laboratories.
小额外标记染色体（sSMC）常与发育异常相关，约60%的病例中畸形为新发。使用各种探针的荧光原位杂交（FISH）技术为分析和鉴定sSMC提供了可能，这对产前诊断和遗传咨询非常重要。我们现在介绍一种结合传统显带和经典FISH技术来识别sSMC起源和结构的特定策略。基于该策略，在一系列15792例产前核型分析中，诊断出20例sSMC病例（患病率为每1000例中有1.26例）。其中18例通过使用商业探针和染色体探针多探针-I系统进行FISH完全分析。在20个sSMC中，12个有随体（10个双随体和2个单随体）（60%），8个无随体（6个环状和2个等臂染色体）（40%）。sSMC大多源自15号染色体（10/20）（50%）。通过各种显带和FISH技术在13例中发现了常染色质物质，而在20个sSMC中的6个中没有常染色质物质的证据。15例可评估亲代核型，其中仅3例（20%）发现家族遗传。我们得出结论，所提出的识别和鉴定sSMC的策略是准确的，对于设备一般的细胞遗传学实验室来说，是新型FISH技术的一个很好的替代方法。
