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Frauke Coppieters, Annelot Baert, Caroline Van Cauwenbergh, Miriam Bauwens, Sarah De Jaegere, Thomy de Ravel, Françoise Meire, Bart Leroy, Elfride De Baere; Regulatory mutations in the 5’UTR of NMNAT1, encoding the nuclear isoform of nicotinamide nucleotide adenylyltransferase 1, cause Leber Congenital Amaurosis. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1313. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Leber Congenital Amaurosis (LCA) is the earliest inherited retinal dystrophy (RD). Recently, coding mutations in NMNAT1 uncovered this gene as the causal disease gene for the LCA9 locus (Falk et al. 2012). In this study, we aimed to identify the genetic defect in an LCA9-linked consanguineous Sub-Saharan African family (F1) and determine the contribution of NMNAT1 mutations in pre-screened LCA patients.
The proband of F1 underwent massive parallel sequencing (MPS) of all coding and promotor regions located in the 4 largest IBD regions (NimbleGen Sequence Capture 385K array, Roche GS FLX Titanium). NMNAT1 expression analysis was performed on leukocyte cDNA with qPCR. NMNAT1 Sanger sequencing was performed on gDNA (exons) and cDNA. F1 and F2 underwent thorough phenotyping.
MPS identified a novel homozygous 5’UTR variant in F1, c.-70A>T, which segregated with disease. This variant was predicted to alter 5’UTR secondary structure. Sequencing of c.-70A>T on cDNA revealed loss of heterozygosity in three heterozygous carriers of F1, suggesting NMNAT1 mRNA degradation. Subsequent sequencing of NMNAT1 in 76 unrelated probands with LCA or early-onset RD revealed mutations in 6 additional probands. Of note, a second 5’UTR variant, c.-69C>T, was found in homozygous state in a Moroccan LCA patient. Interestingly, it is located 1 nucleotide downstream of c.-70A>T and predicted to cause similar aberrant folding. In both F1 and F2, significantly lower mRNA expression was shown for the homozygous carriers in comparison with healthy controls. Moreover, phenotypic evaluation of both families revealed LCA with evolutive macular involvement, typical for NMNAT1-related disease. Luciferase assays are currently ongoing for both 5’UTR variants. Lastly, three probands were compound heterozygous for known mutations, whereas two other probands were found to carry a single heterozygous missense variant. Resequencing of the entire genomic region and copy number screening is currently ongoing.
In conclusion, this study sustained the role of coding NMNAT1 mutations in LCA. Moreover, the identification of two neighboring 5’UTR variants in NMNAT1 makes this the first study to link 5’UTR regulatory variants to LCA with macular involvement. Overall, this study may impact upon the role of 5’UTR variations in other RDs in general.
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