Analysis of molecular abnormalities in DiGeorge syndrome

DiGeorge综合征（DGS）和圆锥动脉干异常面容综合征的微缺失定位于22 q11。为了分离这些综合征的相关基因，从含有完整的人类22号染色体作为其唯一人类成分的体细胞杂种中构建了粘粒库。另一个携带不同人类染色体易位的体细胞杂种使我们能够将这些染色体定位于22 q11，然后通过剂量分析选择位于微缺失中的染色体。为了进一步分离缺失克隆，利用22 q11的显微切割技术构建了微克隆文库，并通过剂量分析筛选出缺失克隆。通过对粘粒文库的筛选和粘粒步移，我们获得了两个粘粒重叠群，并通过荧光原位杂交鉴定了它们的顺序。采用直接选择法从胎脑cDNA文库中获得了一个4.3kb的cDNA。序列分析表明，该基因的开放阅读框编码552个氨基酸，具有DNA结合蛋白的特征，如碱性亮氨酸拉链结构域。被命名为LZTR-1的基因在几个重要的胎儿器官中转录，在大多数患者中被证明是半合子缺失的，但在GM 00980中没有，它有一个缺失，划定了最短的重叠区域。然而，它的几个结构特征确定它作为转录因子表明，它在胚胎发生中起着至关重要的作用，该基因的单倍不足可能部分与DGS的发展。

The microdeletion in DiGeorge syndrome(DGS) and conotruncal anomaly face syndrome has been localized at 22q11. In order to iosolate responsible gene for these syndromes, cosmid library was constructed from the somatic cell hybrid containing human intact chromosome 22 as its only human component. Another somatic cell hybrids carrying a different human chromosome translocation allowed us to assign some of these cosmids to 22q11, and then the cosmids which are located in the microdeletion were selected by dosage analysis. Further to isolate deleted clones, microclone library was constructed with the aid of microdissection of 22q11, and the deleted clones were also selected by dosage analysis. Screening of cosmid library and subsequent cosmid walking allowed us to obtain two cosmid contigs, whose order was identified by fluorescence in situ hybridization. By direct selection strategy, a 4.3kb cDNA was obtained from fetal brain cDNA library. Sequence analysis of the cDNA revealed an open reading frame encoding 552 amino acids which had several characteristics of DNA-binding proteins, such as basic-leucine-zipper domain. The gene, designated LZTR-1, which was transcribed in several essential fetal organs, proved to be hemizygously deleted in most patients, but not in GM00980, which has a deletion that demarcates the shortest region of overlap. However, several of its structural characteristics identifying it as transcriptional factor suggest that it plays a crucial role in embryogenesis and that haploinsufficiency of this gene may be partly related to development of DGS.