Nelle Heike, Schreyer Isolde, Ewers Elisabeth, Mrasek Kristin, Kosyakova Nadezda, Merkas Martina, Hamid Ahmed Basheer, Fahsold Raimund, Ujfalusi Anikó, Anderson Jasen, Rubtsov Nikolai, Küchler Alma, von Eggeling Ferdinand, Hentschel Julia, Weise Anja, Liehr Thomas
Institute of Human Genetics and Anthropology, Jena University Hospital, 07740 Jena, Germany.
Mol Med Rep. 2010 Jul-Aug;3(4):571-4. doi: 10.3892/mmr_00000299.
Mental retardation is correlated in approximately 0.4% of cases with the presence of a small supernumerary marker chromosome (sSMC). However, here we report a case of a carrier of a heterochromatic harmless sSMC with fragile X syndrome (Fra X). In approximately 2% of sSMC cases, similar heterochromatic sSMC were observed in a clinically abnormal carriers. In a subset of such cases, uniparental disomy (UPD) of the corresponding sister chromosomes was shown to be the cause of mental retardation. For the remainder of the cases, including the present one, the sSMC was just a random finding not related to the clinical phenotype. Thus, it is proposed to test patients with heterochromatic sSMC and mental retardation of unclear cause as follows: i) exclude UPD, ii) test for Fra X as it is a major cause of inherited mental retardation, and iii) perform chip-based assays or tests for special genetic diseases according to the phenotype. In any case, the diagnosis of a cytogenetic aberration such as an sSMC should not automatically be considered the resolution of a clinical case.
智力迟钝在约0.4%的病例中与小的额外标记染色体（sSMC）的存在相关。然而，我们在此报告一例携带异染色质无害sSMC且患有脆性X综合征（Fra X）的病例。在约2%的sSMC病例中，在临床异常携带者中观察到类似的异染色质sSMC。在这类病例的一个子集中，相应姐妹染色体的单亲二体性（UPD）被证明是智力迟钝的原因。对于其余病例，包括本病例，sSMC只是一个与临床表型无关的随机发现。因此，建议对携带异染色质sSMC且病因不明的智力迟钝患者进行如下检测：i）排除UPD，ii）检测Fra X，因为它是遗传性智力迟钝的主要原因，iii）根据表型进行基于芯片的检测或特殊遗传疾病检测。在任何情况下，细胞遗传学异常（如sSMC）的诊断不应自动被视为临床病例的解决方案。
