Mendell J T, Panicker S G, Tsao C Y, Feng B, Sahenk Z, Marzluf G A, Mendell J R
Department of Biochemistry, Ohio State University, 1654 Upham Drive, Columbus 43210, Ohio, USA.
Hum Mutat. 1998;12(2):135. doi: 10.1002/(SICI)1098-1004(1998)12:2<135::AID-HUMU10>3.0.CO;2-6.
The laminina2-chain gene (LAMA2) encodes a basal lamina protein, laminina2, known to be deficient in one form of congenital muscular dystrophy (CMD). In a laminina2 deficient-CMD patient, we screened the entire LAMA2 cDNA (953bp) by reverse transcriptase polymerase chain reaction combined with single strand conformational polymorphism analysis. Direct sequencing of aberrant conformers in this patient revealed two loss-of-function mutations, consistent with autosomal recessive inheritance. The patient had two novel heterozygous mutations: 1) an exon 4 nonsense mutation caused by a G-->A substitution at cDNA position 547, changing the TGG codon for tryptophan into a TGA stop codon (W166X) in the N-terminus domain VI;ii) an exon 54 frameshift mutation due to a deletion of nucleotide 'C' at cDNA position 7707 (S2553Y), resulting in a premature stop codon (V2587X) in exon 55 in the globular G domain of laminina2 at the C-terminus. These mutations cause a disruption of the open reading frame of LAMA2. The absence of laminina2 observed in the patient's muscle biopsy could result from diminished levels of the LAMA2 transcript. Alternatively, the mutations might lead to translation of a truncated laminina2. By either mechanism the phenotype of congenital muscular dystrophy is believed to be the result of disruption of linkage between the extracellular matrix and the dystrophin glycoprotein complex.
层粘连蛋白α2链基因（LAMA2）编码一种基底膜蛋白——层粘连蛋白α2，已知在一种先天性肌营养不良（CMD）中缺乏。在一名层粘连蛋白α2缺乏的CMD患者中，我们通过逆转录聚合酶链反应结合单链构象多态性分析对整个LAMA2 cDNA（953bp）进行了筛查。对该患者异常构象体的直接测序揭示了两个功能丧失性突变，符合常染色体隐性遗传。该患者有两个新的杂合突变：1）外显子4无义突变，由cDNA位置547处的G→A替换引起，将N端结构域VI中色氨酸的TGG密码子变为TGA终止密码子（W166X）；ii）外显子54移码突变，由于cDNA位置7707处核苷酸“C”的缺失（S2553Y），导致层粘连蛋白α2 C端球状G结构域中外显子55出现提前终止密码子（V2587X）。这些突变导致LAMA2开放阅读框的破坏。在患者肌肉活检中观察到的层粘连蛋白α2缺失可能是由于LAMA2转录水平降低所致。或者，这些突变可能导致截短的层粘连蛋白α2的翻译。无论哪种机制，先天性肌营养不良的表型被认为是细胞外基质与肌营养不良糖蛋白复合物之间连接破坏的结果。
