Bartsch O, Petersen M B, Stuhlmann I, Mau G, Frantzen M, Schwinger E, Antonarakis S E, Mikkelsen M
Institut für Klinische Genetik, Universitäts Klinikum der Technischen Universität, Dresden, Germany.
J Med Genet. 1994 Jul;31(7):534-40. doi: 10.1136/jmg.31.7.534.
Two cases of growth failure, microcephaly, facial dysmorphism, muscular hypertonia, and severe psychomotor retardation are described. At birth, both cases had cytogenetic mosaicism in lymphocytes and skin fibroblasts, in case 1 ring chromosome 21 and monosomy 21 and in case 2, deletion of chromosome 21 and monosomy 21. At a later age the lymphocyte karyotype changed almost completely to 46,XX, but the fibroblast karyotype remained as before. DNA polymorphism analysis described elsewhere indicated that the 46,XX lymphocytes contained two identical chromosomes 21 (isodisomy), in case 1 inherited from the father and in case 2 from the mother. The isodisomy was the result of duplication of a chromosome in mitosis after the loss of the homologous abnormal chromosome ("compensatory isodisomy"). We report here that this cytogenetic mechanism can result in false normal cytogenetic findings. The phenotypes were attributed to the cells with monosomy 21 in case 1 and to the deletion and monosomy of chromosome 21 in case 2.
本文描述了两例生长发育迟缓、小头畸形、面部畸形、肌张力亢进和严重精神运动发育迟缓的病例。出生时，两例病例的淋巴细胞和皮肤成纤维细胞均存在细胞遗传学嵌合体，病例1为21号环状染色体和21号单体，病例2为21号染色体缺失和21号单体。在稍大年龄时，淋巴细胞核型几乎完全变为46,XX，但成纤维细胞核型仍保持不变。其他地方描述的DNA多态性分析表明，46,XX淋巴细胞包含两条相同的21号染色体（等二体），病例1的来自父亲，病例2的来自母亲。等二体是有丝分裂中同源异常染色体丢失后染色体复制的结果（“补偿性等二体”）。我们在此报告，这种细胞遗传学机制可导致细胞遗传学检查结果出现假正常情况。病例1的表型归因于具有21号单体的细胞，病例2的表型归因于21号染色体的缺失和单体。
