de Kievit P, van Geel M, van der Wielen M J, Bakker E, Padberg G W, Frants R R, van der Maarel S M
Center for Human and Clinical Genetics, Leiden University Medical Center, The Netherlands.
Ann Neurol. 2001 Dec;50(6):816-9. doi: 10.1002/ana.10057.
Facioscapulohumeral muscular dystrophy is caused by partial deletion of the D4Z4 repeat array on chromosome 4q35. Genetic diagnosis is based on sizing of this repeat array, which is complicated by cross-hybridization of a homologous polymorphic repeat array on chromosome 10 and by the frequent exchanges between these chromosomal regions. The restriction enzyme XapI optimizes the diagnosis of facioscapulohumeral muscular dystrophy by uniquely digesting 4-derived repeat units and leaving 10-derived repeat units undigested, thus complementing BlnI, which uniquely digests 10-derived repeat units. A triple analysis with EcoRI, EcoRI/BlnI, and XapI unequivocally allows characterization of each of the four alleles, whether homogeneous or hybrid. This is particularly useful in the case of identical sized 4-derived and 10-derived arrays, in situations of suspected facioscapulohumeral muscular dystrophy with nonstandard allele configurations, and for assignment of hybrid fragments to their original alleles.
面肩肱型肌营养不良症由4号染色体长臂35区（4q35）的D4Z4重复序列部分缺失引起。基因诊断基于该重复序列的大小测定，由于10号染色体上同源多态性重复序列的交叉杂交以及这些染色体区域之间的频繁交换，使得该过程变得复杂。限制性内切酶XapI通过特异性消化源自4号染色体的重复单元而不消化源自10号染色体的重复单元，优化了面肩肱型肌营养不良症的诊断，从而补充了BlnI，后者特异性消化源自10号染色体的重复单元。用EcoRI、EcoRI/BlnI和XapI进行三重分析能够明确表征四个等位基因中的每一个，无论其是纯合还是杂合。这在源自4号染色体和源自10号染色体的阵列大小相同的情况下、在怀疑面肩肱型肌营养不良症且等位基因构型不标准的情况下以及将杂交片段归属于其原始等位基因时特别有用。
