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Scott H Greenwald, Kinga Maria Bujakowska, Emily Place, Eric Pierce; An Expanded NMNAT1 Allele Containing a Partial Gene Duplication is Associated with Leber Congenital Amaurosis. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3286.
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© ARVO (1962-2015); The Authors (2016-present)
Mutations in the NMNAT1 gene have been identified as a relatively common cause of the severe, early onset retinal degeneration Leber congenital amaurosis (LCA). Clinical genetic diagnostic testing identified one previously reported missense mutation (c.769G>A, p.Glu257Lys) in NMNAT1 in a 1 year old patient with LCA, and suggested that the second mutant allele could involve a copy number variation (CNV) in the NMNAT1 gene. Further analyses were undertaken to define the CNV in this patient.
RNA samples extracted from whole blood collected from the 1-year-old LCA patient and his parents were reversed transcribed into cDNA. Standard polymerase chain reaction (PCR) was used to amplify portions of the NMNAT1 gene in all subjects to define the putative CNV. Sanger sequencing was used to confirm the c.769G>A missense mutation.
PCR reactions using a forward primer in the 5’UTR and a reverse primer in the 3’UTR of NMNAT1 generated a normal length product (978bp) in all three subjects. An additional ~1.5kb PCR product was also observed in both the proband and mother, but not in the father. For all three subjects, PCR reactions using a forward primer within the translated region of exon 2 and a reverse primer within the translated region of exon 5 generated only a normal length product (396bp), suggesting that the CNV consisted of a partial duplication of the NMNAT1 gene. Additional studies are in progress to define the partial duplication in detail. Sequencing of a PCR amplified region of exon 5 showed that the proband and father were each heterozygous for the c.769G>A point mutation.
These studies identified a partial duplication of the NMNAT1 gene as a pathogenic allele in a patient with LCA. This is the first report of a pathogenic CNV in the NMNAT1 gene. The partial duplication appears to consist of an ~500bp portion of NMNAT1. As for other retinal degeneration disease genes, CNVs in NMNAT1 should be considered as possible pathogenic alleles in patients with LCA.
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