Manolakos Emmanouil, Vetro Annalisa, Kefalas Konstantinos, Rapti Stamatia-Maria, Louizou Eirini, Garas Antonios, Kitsos George, Vasileiadis Lefteris, Tsoplou Panagiota, Eleftheriades Makarios, Peitsidis Panagiotis, Orru Sandro, Liehr Thomas, Petersen Michael B, Thomaidis Loretta
Bioiatriki S,A,, Laboratory of Genetics, Athens, Greece.
Mol Cytogenet. 2010 Nov 9;3:22. doi: 10.1186/1755-8166-3-22.
The genetic diagnosis of mental retardation (MR) is difficult to establish and at present many cases remain undiagnosed and unexplained. Standard karyotyping has been used as one of the routine techniques for the last decades. The implementation of Array Comparative Genomic Hybridization (array-CGH) has enabled the analysis of copy number variants (CNVs) with high resolution. Major cohort studies attribute 11% of patients with unexplained mental retardation to clinically significant CNVs. Here we report the use of array-CGH for the first time in a Greek cohort. A total of 82 children of Greek origin with mean age 4.9 years were analysed in the present study. Patients with visible cytogenetic abnormalities ascertained by standard karyotyping as well as those with subtelomeric abnormalities determined by Multiplex Ligation-dependent Probe Amplification (MLPA) or subtelomeric FISH had been excluded.
Fourteen CNVs were detected in the studied patients. In nine patients (11%) the chromosomal aberrations were inherited from one of the parents. One patients showed two duplications, a 550 kb duplication in 3p14.1 inherited from the father and a ~1.1 Mb duplication in (22)(q13.1q13.2) inherited from the mother. Although both parents were phenotypically normal, it cannot be excluded that the dual duplication is causative for the patient's clinical profile including dysmorphic features and severe developmental delay. Furthermore, three de novo clinically significant CNVs were detected (3.7%). There was a ~6 Mb triplication of 18q21.1 in a girl 5 years of age with moderate MR and mild dysmorphic features and a ~4.8 Mb duplication at (10)(q11.1q11.21) in a 2 years old boy with severe MR, multiple congenital anomalies, severe central hypotonia, and ataxia. Finally, in a 3 year-old girl with microcephaly and severe hypotonia a deletion in (2)(q31.2q31.3) of about ~3.9 Mb was discovered. All CNVs were confirmed by Fluorescence in situ hybridization (FISH). For the remaining 9 patients the detected CNVs (inherited duplications or deletions of 80 kb to 800 kb in size) were probably not associated with the clinical findings.
Genomic microarrays have within the recent years proven to be a highly useful tool in the investigation of unexplained MR. The cohorts reported so far agree on an around 11% diagnostic yield of clinically significant CNVs in patients with unexplained MR. Various publicly available databases have been created for the interpretation of identified CNVs and parents are analyzed in case a rare CNV is identified in the child. We have conducted a study of Greek patients with unexplained MR and confirmed the high diagnostic value of the previous studies. It is important that the technique becomes available also in less developed countries when the cost of consumables will be reduced.
智力发育迟缓（MR）的基因诊断很难确立，目前许多病例仍未得到诊断且原因不明。在过去几十年中，标准核型分析一直是常规技术之一。阵列比较基因组杂交（array-CGH）技术的应用使得能够高分辨率地分析拷贝数变异（CNV）。主要队列研究表明，11%病因不明的智力发育迟缓患者存在具有临床意义的CNV。在此，我们首次报告在希腊队列中使用array-CGH技术。本研究共分析了82名希腊裔儿童，平均年龄4.9岁。通过标准核型分析确定有明显细胞遗传学异常的患者以及通过多重连接依赖探针扩增（MLPA）或亚端粒荧光原位杂交（FISH）确定有亚端粒异常的患者均被排除。
在所研究的患者中检测到14个CNV。9名患者（11%）的染色体畸变是从父母一方遗传而来。一名患者出现两个重复，一个550 kb的3p14.1重复片段遗传自父亲，一个约1.1 Mb的（22）（q13.1q13.2）重复片段遗传自母亲。尽管父母双方表型正常，但不能排除双重重复是导致患者包括畸形特征和严重发育迟缓在内的临床症状的原因。此外，检测到3个新发的具有临床意义的CNV（3.7%）。一名5岁患有中度智力发育迟缓及轻度畸形特征的女孩存在18q21.1约6 Mb的三倍体重复，一名2岁患有严重智力发育迟缓、多种先天性异常、严重中枢性肌张力低下和共济失调的男孩存在（10）（q11.1q11.21）约4.8 Mb的重复。最后，在一名患有小头畸形和严重肌张力低下的3岁女孩中发现（2）（q31.2q31.3）约3.9 Mb的缺失。所有CNV均通过荧光原位杂交（FISH）得到证实。对于其余9名患者，检测到的CNV（大小为80 kb至800 kb的遗传重复或缺失）可能与临床发现无关。
近年来，基因组微阵列已被证明是调查病因不明的智力发育迟缓的一种非常有用的工具。目前报道的队列研究一致认为，病因不明的智力发育迟缓患者中具有临床意义的CNV的诊断率约为11%。已经创建了各种公开可用的数据库用于解释已识别出的CNV，并且如果在儿童中发现罕见的CNV，则会对父母进行分析。我们对希腊病因不明的智力发育迟缓患者进行了一项研究，并证实了先前研究的高诊断价值。当耗材成本降低时，这项技术在欠发达国家也能应用很重要。
