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Case Reports
. 2017 Feb 2;100(2):343-351.
doi: 10.1016/j.ajhg.2016.12.013. Epub 2017 Jan 26.

A Recurrent De Novo Variant in NACC1 Causes a Syndrome Characterized by Infantile Epilepsy, Cataracts, and Profound Developmental Delay

Collaborators, Affiliations
Case Reports

A Recurrent De Novo Variant in NACC1 Causes a Syndrome Characterized by Infantile Epilepsy, Cataracts, and Profound Developmental Delay

Kelly Schoch et al. Am J Hum Genet. .

Abstract

Whole-exome sequencing (WES) has increasingly enabled new pathogenic gene variant identification for undiagnosed neurodevelopmental disorders and provided insights into both gene function and disease biology. Here, we describe seven children with a neurodevelopmental disorder characterized by microcephaly, profound developmental delays and/or intellectual disability, cataracts, severe epilepsy including infantile spasms, irritability, failure to thrive, and stereotypic hand movements. Brain imaging in these individuals reveals delay in myelination and cerebral atrophy. We observe an identical recurrent de novo heterozygous c.892C>T (p.Arg298Trp) variant in the nucleus accumbens associated 1 (NACC1) gene in seven affected individuals. One of the seven individuals is mosaic for this variant. NACC1 encodes a transcriptional repressor implicated in gene expression and has not previously been associated with germline disorders. The probability of finding the same missense NACC1 variant by chance in 7 out of 17,228 individuals who underwent WES for diagnoses of neurodevelopmental phenotypes is extremely small and achieves genome-wide significance (p = 1.25 × 10-14). Selective constraint against missense variants in NACC1 makes this excess of an identical missense variant in all seven individuals more remarkable. Our findings are consistent with a germline recurrent mutational hotspot associated with an allele-specific neurodevelopmental phenotype in NACC1.

Keywords: NACC1; cataracts; developmental/intellectual disabilities; epilepsy; irritability; microcephaly; stereotypy; whole-exome sequencing.

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Figures

Figure 1
Figure 1
Clinical and Neuroradiologic Characteristics of the Seven Probands (A) Individual 1 at 20 months of age. (B) Individual 2 at 12 years of age. (C) Individual 3 at 9 years of age. (D) Individual 4 at 3.5 years of age. (E) Individual 6 at 13 months of age. (F) Individual 7 at 12 years of age. (G–P) Axial T1 and T2 brain MRI images demonstrating mildly delayed myelination in individual 1 at 9 months old (G, L); severely delayed myelination and volume loss in individual 4 at 3 years old (H, M); severely delayed myelination and minimal volume loss in individual 5 at 10 years old (I, N); volume loss with normal myelination in individual 6 at 12 months old (J, O); and normal myelination and brain volume in individual 7 at 10 years old (K, P).
Figure 2
Figure 2
Recurrent De Novo c.892C>T (p.Arg298Trp) Missense Change in NACC1 Observed in All Seven Probands (A) Family pedigrees for individuals 1–7 with de novo events in each affected proband. Note that unaffected sibling of individual 5 was also sequenced and found not to have the de novo variant. (B) Sanger sequencing traces for individuals 1–7 showing the heterozygous de novo C-T transition at the c.892 CGG codon encoding arginine, resulting in a TGG codon encoding tryptophan. Individual 7 was found to be mosaic for this variant in peripheral blood. Numbers below each individual represent allele count of alternative to reference alleles from exome sequencing.
Figure 3
Figure 3
Predicted Protein Change for the De Novo NACC1 Variant in Context of Protein Domains (A) Amino acid sequence alignment of human NAC1 with zebrafish, Xenopus, and mouse. The BEN and BTB domains are shown, and the location of the p.Arg298Trp missense change is depicted by a red star. The amino acid residue is conserved in all four species and is within a stretch of identical residues. (B) The Arg298 residue occurs within NAC1 between the BTB domain and BEN domain, closer to the BEN domain. A single p.Arg468Cys change (gray-green lollipop) has been noted in a large cohort study of intellectual disability, while the c.946+2T>C (A316 splice) change (black lollipop with asterisk to indicate the position of the splice change) has been noted in a cohort of patients with autism spectrum disorder. Interestingly, a variant involving the same amino acid, converting from Arg to Leu (c.893G>T [p.Arg298Leu]), has been observed once in the ExAC database and in four individuals in gnomAD, with undefined clinical information. Spanning this region is a microdeletion, shown as a gray bar under the gene domain structure.

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