Friday, May 25, 2018

NFIX mutations

Inspired by a patient

Trimouille A, Houcinat N, Vuillaume ML, Fergelot P, Boucher C, Toutain J, Caignec CL, Vincent M, Nizon M, Andrieux J, Vanlerberghe C, Delobel B, Duban B, Mansour S, Baple E, McKeown C, Poke G, Robertshaw K, Fifield E, Fabretto A, Pecile V, Gasparini P, Carrozzi M, Lacombe D, Arveiler B, Rooryck C, Moutton S. 19p13 microduplications encompassing NFIX are responsible for intellectual
disability, short stature and small head circumference. Eur J Hum Genet. 2018 Jan;26(1):85-93.

Syndromes caused by copy number variations are described as reciprocal when they result from deletions or duplications of the same chromosomal region. When comparing the phenotypes of these syndromes, various clinical features could be described as reversed, probably due to the opposite effect of these imbalances on the expression of genes located at this locus. The NFIX gene codes for a transcription factor implicated in neurogenesis and chondrocyte differentiation. Microdeletions and loss of function variants of NFIX are responsible for Sotos syndrome-2 (also described as Malan syndrome), a syndromic form of intellectual disability associated with overgrowth and macrocephaly. Here, we report a cohort of nine patients harboring microduplications encompassing NFIX. These patients exhibit variable intellectual disability, short stature and small head circumference, which can be described as a reversed Sotos syndrome-2 phenotype. Strikingly, such a reversed phenotype has already been described in patients harboring microduplications encompassing NSD1, the gene whose deletions and loss-of-function variants are responsible for classical Sotos syndrome. Even though the type/contre-type concept has been criticized, this model seems to give a plausible explanation for the pathogenicity of 19p13 microduplications, and the common phenotype observed in our cohort.

Lu Y, Chong PF, Kira R, Seto T, Ondo Y, Shimojima K, Yamamoto T. Mutations in NSD1 and NFIX in Three Patients with Clinical Features of Sotos Syndrome and Malan Syndrome. J Pediatr Genet. 2017 Dec;6(4):234-237.

Mutations in nuclear receptor SET domain-containing protein 1 gene ( NSD1 ) are related to Sotos syndrome, which is characterized by overgrowth, macrocephaly, distinctive features, and neurodevelopmental disabilities. On the other hand, mutations in the nuclear factor I/X gene ( NFIX ) can lead to Malan syndrome, also known as Sotos-like syndrome, or to the Marshall-Smith syndrome. In this study, using next generation sequencing (NGS), we identified de novo mutations in NSD1 and NFIX in three patients with developmental disabilities associated with overgrowth or macrocephaly. Overall, we confirmed that clinical entities of congenital malformation syndromes can be expanded by molecular diagnoses via NGS.

Oshima T, Hara H, Takeda N, Hasumi E, Kuroda Y, Taniguchi G, Inuzuka R, Nawata K, Morita H, Komuro I. A novel mutation of NFIX causes Sotos-like syndrome (Malan syndrome) complicated with thoracic aortic aneurysm and dissection. Hum Genome Var. 2017 Jun 1;4:17022.

Malan syndrome has recently been characterized to present Sotos-like phenotypes, such as intellectual disability and macrocephaly, with mutations in the NFIX gene. Herein, we report a 38-year-old patient with a novel single adenine insertion mutation in exon 2 of the NFIX gene (c.290_291insA). He developed early-onset thoracic aortic aneurysm and dissection, which was a rare complication but deserves particular attention in relatively long-lived patients with Sotos-like phenotypes.

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