The role of immunocytochemistry and linkage analysis in the prenatal diagnosis of merosin-deficient congenital muscular dystrophy

Complete or partial deficiency of the laminin alpha 2 chain of merosin has been demonstrated in a porportion of children with classical congenital muscular dystrophy and linkage to the laminin alpha 2 chain gene (LAMA2) on chromosome 6q2 has been established. As the laminin alpha 2 chain is also expressed in the trophoblast, its detection and linkage analysis are useful tools for prenatal diagnosis. We report our experience of seven prenatal diagnoses in families with partial deficiency or total absence of the laminin alpha 2 chain in the muscle of the propositi. In five instances, expression of the laminin alpha 2 chain in the trophoblast was normal and linkage data suggested that the fetuses were unaffected. In one family, the immunocytochemical studies of the trophoblast showed the absence of laminin alpha 2, suggesting that the fetus was affected. Linkage analysis confirmed that the fetus had inherited the two at-risk haplotypes. In one family with partial laminin alpha 2 chain deficiency, the haplotype analysis was hampered by maternal DNA contamination. Immunocytochemical analysis of chorionic villus sampling showed a reduction in laminin alpha 2 expression. The pregnancy was presumed to be at high-risk and terminated. However, subsequent analysis of fetal DNA indicated that the fetus was probably heterozygous. Our data suggest that immunocytochemical analysis of the trophoblast can detect abnormalities in affected fetuses and gives normal results in unaffected and carrier fetuses. Nevertheless, we recommend that linkage analysis to the LAMA2 locus is also studied in all cases.