Canevini M P, Sgro V, Zuffardi O, Canger R, Carrozzo R, Rossi E, Ledbetter D, Minicucci F, Vignoli A, Piazzini A, Guidolin L, Saltarelli A, dalla Bernardina B
Centro Regionale Epilessia, Ospedale San Paolo, Università degli Studi, Milan, Italy.
Epilepsia. 1998 Sep;39(9):942-51. doi: 10.1111/j.1528-1157.1998.tb01443.x.
The chromosome 20 ring [r(20)] is a rare chromosomal disorder without clear phenotypical markers. We describe the electroclinical pattern in a group of patients with r(20).
We observed 3 patients (a boy, patient 1; his mother, patient 2; and an unrelated man, patient 3), performing prolonged video-EEG and cytogenetic studies and fluorescent in situ hybridization (FISH) with chromosome-specific telomeric probes.
All 3 patients had a very similar abnormal electroclinical pattern characterized by long bursts or trains of rhythmic theta waves, which were sharply contoured or had a notched appearance (with no detectable clinical correlate), and generalized spike waves (SW) associated with seizures of probable frontotemporal origin (SFT). In all 3 patients, the cytogenetic analysis of T lymphocytes showed mosaicism with a normal cell line and a second cell line with a chromosome 20, although the latter was little represented in patients 2 and 3. A few cells with a single chromosome 20 were also found. The same cytogenetic findings were confirmed in the lymphoblastoid cell line of patient 1 and in the fibroblasts of patient 3. FISH with chromosome-specific telomeric probes and TTAGGG sequences demonstrated the integrity of the ring chromosomes.
The clinical picture of these patients appears to be related to the instability of the r(20)-generating cells monosomic for chromosome 20 and is thus haploinsufficient for a gene. In these patients, the electroclinical pattern of theta waves (probably unrelated to epilepsy) and the SW and SFT, even with mild mental retardation (MR) or no MR and without dysmorphic features, suggest that the r(20) syndrome may be present.
20号环状染色体[r(20)]是一种罕见的染色体疾病，没有明确的表型标记。我们描述了一组r(20)患者的电临床模式。
我们观察了3例患者（1例男孩，患者1；他的母亲，患者2；以及一名无关男性，患者3），进行了长时间视频脑电图和细胞遗传学研究，以及使用染色体特异性端粒探针的荧光原位杂交（FISH）。
所有3例患者都有非常相似的异常电临床模式，其特征为长时间的节律性θ波爆发或序列，这些θ波轮廓清晰或有缺口外观（无明显临床关联），以及与可能起源于额颞叶的癫痫发作相关的全身性棘波（SW）。在所有3例患者中，T淋巴细胞的细胞遗传学分析显示存在嵌合体，有一个正常细胞系和另一个含有20号染色体的细胞系，尽管在患者2和3中后者占比很少。还发现了一些含有单个20号染色体的细胞。在患者1的淋巴母细胞系和患者3的成纤维细胞中证实了相同的细胞遗传学结果。使用染色体特异性端粒探针和TTAGGG序列的FISH显示环状染色体的完整性。
这些患者的临床症状似乎与产生r(20)的细胞的不稳定性有关，这些细胞对于20号染色体是单体型的，因此对于一个基因来说是单倍体不足的。在这些患者中，θ波（可能与癫痫无关）以及SW和额颞叶癫痫发作的电临床模式，即使伴有轻度智力障碍（MR）或无MR且无畸形特征，也提示可能存在r(20)综合征。
