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Hybrids monosomal for human chromosome 5 reveal the presence of a spinal muscular atrophy (SMA) carrier with two SMN1 copies on one chromosome

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Abstract.

We have analyzed the survival motor neuron gene (SMN1) dosage in 100 parents of children with homozygous SMN1 deletions. Of these parents, 96 (96%) demonstrated the expected one-copy SMN1 carrier genotype. However, four parents (4%) were observed to have a normal two-copy SMN1 dosage. The presence of two intact SMN1 genes in the parent of an affected child indicates either the occurrence of a de novo mutation event or a situation in which one chromosome has two copies of SMN1, whereas the other is null. We have separated individual chromosomes from two of these parents with two-copy SMN1 dosage by somatic cell hybridization and have employed a modified quantitative dosage assay to provide direct evidence that one parent is a two-copy/zero-copy SMN1 carrier, whereas the other parent had an affected child as the result of a de novo mutation. These findings are important for assessing the recurrence risk of parents of children with spinal muscular atrophy and for providing accurate family counseling.

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Mailman, M., Hemingway, T., Darsey, R. et al. Hybrids monosomal for human chromosome 5 reveal the presence of a spinal muscular atrophy (SMA) carrier with two SMN1 copies on one chromosome. Hum Genet 108, 109–115 (2001). https://doi.org/10.1007/s004390000446

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  • DOI: https://doi.org/10.1007/s004390000446

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