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Am J Hum Genet. 2000 Sep;67(3):750-4. Epub 2000 Jul 27.

Rare etiology of autosomal recessive disease in a child with noncarrier parents.

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Center for Human Genetics, Department of Pediatrics, Boston University School of Medicine, Boston, MA, 02118, USA.


A child with maple syrup urine disease type 2 (MSUD2) was found to be homozygous for a 10-bp MSUD2-gene deletion on chromosome 1. Both purported parents were tested, and neither carries the gene deletion. Polymorphic simple-sequence repeat analyses at 15 loci on chromosome 1 and at 16 loci on other chromosomes confirmed parentage and revealed that a de novo mutation prior to maternal meiosis I, followed by nondisjunction in maternal meiosis II, resulted in an oocyte with two copies of the de novo mutant allele. Fertilization by a sperm that did not carry a paternal chromosome 1 or subsequent mitotic loss of the paternal chromosome 1 resulted in the propositus inheriting two mutant MSUD2 alleles on two maternal number 1 chromosomes.

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