Inserm, U956, Faculté de Médecine Pierre et Marie Curie, Paris, France.
Eur J Hum Genet. 2011 Apr;19(4):452-7. doi: 10.1038/ejhg.2010.212. Epub 2011 Jan 19.
Mutation of the LARGE gene is the rarest of the six known genetic causes of α-dystroglycanopathy. We report further a family with MDC1D due to a complex genomic rearrangement that was not apparent on standard sequencing of LARGE. Two sisters in a consanguineous family had moderate mental retardation and cerebellar malformations, together with dystrophic changes and markedly reduced α-dystroglycan glycosylation staining on muscle biopsy. There was homozygous linkage to the LARGE locus but sequencing of LARGE coding regions was normal. Analysis of LARGE cDNA showed an abnormal sequence inserted between exons 10 and 11, in most of the transcripts, predicted to introduce a premature stop codon. The abnormal sequence mapped to a spliced EST (DA935254) of unknown function, normally located at 100 kb centromeric of LARGE on chromosome 22q12.3. Quantitative PCR analysis of the EST and adjacent regions showed twice the normal copy number in patients' genomic DNA samples, consistent with a large intra-chromosomal duplication inserted into intron 10 of LARGE in a homozygous state. This insertion was associated with deletion of a central region of intron 10, but the exact break points of the deletion/duplication were not found, suggesting that an even more complex rearrangement may have occurred. The exact function of LARGE, a golgi protein, remains uncertain. POMT and POMGnT enzyme activities were normal in patients' lymphoblast cells, suggesting that defects in LARGE do not affect the initiation of O-mannosyl glycans.
LARGE 基因突变是已知六种 α- 连接糖蛋白病遗传病因中最罕见的一种。我们进一步报告了一个 MDC1D 家系，其致病原因为复杂的基因组重排，标准 LARGE 测序未能发现该重排。一个近亲家系中的两个姐妹存在中度智力障碍和小脑畸形，同时存在肌肉活检的营养不良性改变和明显减少的α- 连接糖蛋白糖基化染色。LARGE 基因座存在纯合连锁，但 LARGE 编码区测序正常。LARGE cDNA 分析显示，大多数转录本中 10 号和 11 号外显子之间插入了异常序列，预测会引入提前终止密码子。异常序列与一个 spliced EST（DA935254）相关，该 EST 功能未知，通常位于 22q12.3 染色体的 LARGE 基因座着丝粒侧 100kb 处。EST 和邻近区域的定量 PCR 分析显示，患者基因组 DNA 样本中该 EST 的拷贝数是正常的两倍，提示一个大型的染色体内部重复序列以纯合状态插入 LARGE 的 10 号内含子中。这种插入与 10 号内含子中心区域的缺失有关，但缺失/重复的确切断点尚未找到，提示可能发生了更复杂的重排。LARGE 是一种高尔基体蛋白，其确切功能仍不确定。患者的淋巴母细胞中 POMT 和 POMGnT 酶活性正常，提示 LARGE 缺陷不影响 O- 甘露糖聚糖的起始。
