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Eur J Hum Genet. 2010 Apr;18(4):505-8. doi: 10.1038/ejhg.2009.198. Epub 2009 Nov 11.

Single-sperm analysis for recurrence risk assessment of spinal muscular atrophy.

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Unité INSERM U781 Institut de Recherche Necker-Enfants Malades, service de génétique médicale, Hôpital Necker-Enfants Malades (Assistance Publique-Hôpitaux de Paris), Université Paris-Descartes, 75743 Paris Cedex 15, France.


With the detection of a homozygous deletion of the survival motor neuron 1 gene (SMN1), prenatal and preimplantation genetic diagnosis (PGD) for spinal muscular atrophy has become feasible and widely applied. The finding of a de novo rearrangement, resulting in the loss of the SMN1 gene, reduces the recurrence risk from 25% to a lower percentage, the residual risk arising from recurrent de novo mutation or germline mosaicism. In a couple referred to our PGD center because their first child was affected with SMA, the male partner was shown to carry two SMN1 copies. An analysis of the SMN1 gene and two flanking markers was performed on 12 single spermatozoa, to determine whether the father carried a CIS duplication of the SMN1 gene on one chromosome and was a carrier, or if the deletion has occurred de novo. We showed that all spermatozoa that were carriers of the 'at-risk haplotype' were deleted for the SMN1 gene, confirming the carrier status of the father. We provide an original application of single germ cell studies to recessive disorders using coamplification of the gene and its linked markers. This efficient and easy procedure might be useful to elucidate complex genetic situations when samples from other family members are not available.

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