Delineation of a Novel Mirror Syndrome: NFIC Variants Cause Syndromic Intellectual Disability With Macrocephaly.

Variants in NFIC, an NFI-family transcription factor regulating neural stem and progenitor differentiation: de novo SNVs and deletions encompassing the gene, with a dosage-sensitive effect and cranial phenotypes opposite to those of proximal 19p13.3 duplications (mirror-syndrome model).

While NFIA, NFIB and NFIX are already linked to neurodevelopmental disorders, the role of NFIC in human disease remained unclear. The authors assemble the first cohort of 11 individuals with NFIC variants, including four de novo SNVs and seven deletions encompassing the gene, nine of them previously unreported. Genotype-phenotype correlations with critical region mapping were performed, and murine data together with bioinformatic analyses were integrated to explore mechanisms. A core phenotype of syndromic intellectual disability with macrocephaly was delineated, and cranial phenotypes opposite to those of proximal 19p13.3 duplication cases support a dosage-sensitive effect and a mirror-syndrome model.

Synthesis written by Geno'X. For the full original abstract, please refer to the source publication.

NFIC was the last NFI family member without an established clinical association; this first cohort fills the gap and provides a recognisable phenotype, intellectual disability with macrocephaly. Since the locus is already covered by WES and chromosomal microarray, the concrete contribution is interpretive: a 19p13.3 deletion or a de novo SNV previously reported without conclusion can now be qualified. Eleven individuals, a substantial share of them multigenic deletions, remain a fragile basis for attributing the phenotype to NFIC alone — critical region mapping helps but does not replace additional point-variant cases.

Analysis by Dr Thibaut Benquey