Jenne D E, Tinschert S, Reimann H, Lasinger W, Thiel G, Hameister H, Kehrer-Sawatzki H
Max-Planck-Institute of Neurobiology, Department of Neuroimmunology, Martinsried, Germany.
Am J Hum Genet. 2001 Sep;69(3):516-27. doi: 10.1086/323043. Epub 2001 Jul 20.
Homologous recombination between poorly characterized regions flanking the NF1 locus causes the constitutional loss of approximately 1.5 Mb from 17q11.2 covering > or =11 genes in 5%-20% of patients with neurofibromatosis type 1 (NF1). To elucidate the extent of microheterogeneity at the deletion boundaries, we used single-copy DNA fragments from the extreme ends of the deleted segment to perform FISH on metaphase chromosomes from eight patients with NF1 who had large deletions. In six patients, these probes were deleted, suggesting that breakage and fusions occurred within the adjacent highly homologous sequences. Reexamination of the deleted region revealed two novel functional genes FLJ12735 (AK022797) and KIAA0653-related (WI-12393 and AJ314647), the latter of which is located closest to the distal boundary and is partially duplicated. We defined the complete reading frames for these genes and two expressed-sequence tag (EST) clusters that were reported elsewhere and are associated with the markers SHGC-2390 and WI-9521. Hybrid cell lines carrying only the deleted chromosome 17 were generated from two patients and used to identify the fusion sequences by junction-specific PCRs. The proximal breakpoints were found between positions 125279 and 125479 in one patient and within 4 kb of position 143000 on BAC R-271K11 (AC005562) in three patients, and the distal breakpoints were found at the precise homologous position on R-640N20 (AC023278). The interstitial 17q11.2 microdeletion arises from unequal crossover between two highly homologous WI-12393-derived 60-kb duplicons separated by approximately 1.5 Mb. Since patients with the NF1 large-deletion syndrome have a significantly increased risk of neurofibroma development and mental retardation, hemizygosity for genes from the deleted region around the neurofibromin locus (CYTOR4, FLJ12735, FLJ22729, HSA272195 (centaurin-alpha2), NF1, OMGP, EVI2A, EVI2B, WI-9521, HSA272196, HCA66, KIAA0160, and WI-12393) may contribute to the severe phenotype of these patients.
在1型神经纤维瘤病（NF1）患者中，约5%-20%的患者由于NF1基因座两侧特征不明的区域之间发生同源重组，导致17q11.2上约1.5 Mb的片段发生遗传性缺失，该片段包含≥11个基因。为了阐明缺失边界处的微异质性程度，我们使用来自缺失片段两端的单拷贝DNA片段，对8例患有大片段缺失的NF1患者的中期染色体进行荧光原位杂交（FISH）。在6例患者中，这些探针发生了缺失，提示断裂和融合发生在相邻的高度同源序列内。对缺失区域的重新检查发现了两个新的功能基因FLJ12735（AK022797）和KIAA0653相关基因（WI-12393和AJ314647），后者最靠近远端边界且部分重复。我们确定了这些基因以及两个表达序列标签（EST）簇的完整阅读框，这两个EST簇在其他地方有报道且与标记SHGC-2390和WI-9521相关。从两名患者中构建了仅携带缺失的17号染色体的杂交细胞系，并通过连接特异性聚合酶链反应（PCR）鉴定融合序列。在一名患者中，近端断点位于125279和125479位之间，在三名患者中，近端断点位于BAC R-271K11（AC005562）上143000位的4 kb范围内，远端断点位于R-640N20（AC023278）上的精确同源位置。17q11.2间质性微缺失源于两个高度同源的、由约1.5 Mb隔开的WI-12393衍生的60 kb重复子之间的不等交换。由于患有NF1大片段缺失综合征的患者发生神经纤维瘤和智力发育迟缓的风险显著增加，神经纤维瘤蛋白基因座周围缺失区域的基因（CYTOR4、FLJ12735、FLJ22729、HSA272195（centaurin-alpha2）、NF1、OMGP、EVI2A、EVI2B、WI-9521、HSA272196、HCA66、KIAA0160和WI-12393）的半合子状态可能导致这些患者的严重表型。
