NSD1 mutations are the major cause of Sotos syndrome and occur in some cases of Weaver syndrome but are rare in other overgrowth phenotypes

Abstract

Sotos syndrome is a childhood overgrowth syndrome characterized by a distinctive facial appearance, height and head circumference >97th percentile, advanced bone age, and developmental delay. Weaver syndrome is characterized by the same criteria but has its own distinctive facial gestalt. Recently, a 2.2-Mb chromosome 5q35 microdeletion, encompassing NSD1, was reported as the major cause of Sotos syndrome, with intragenic NSD1 mutations identified in a minority of cases. We evaluated 75 patients with childhood overgrowth, for intragenic mutations and large deletions of NSD1. The series was phenotypically scored into four groups, prior to the molecular analyses: the phenotype in group 1 (n=37) was typical of Sotos syndrome; the phenotype in group 2 (n=13) was Sotos-like but with some atypical features; patients in group 3 (n=7) had Weaver syndrome, and patients in group 4 (n=18) had an overgrowth condition that was neither Sotos nor Weaver syndrome. We detected three deletions and 32 mutations (13 frameshift, 8 nonsense, 2 splice-site, and 9 missense) that are likely to impair NSD1 functions. The truncating mutations were spread throughout NSD1, but there was evidence of clustering of missense mutations in highly conserved functional domains between exons 13 and 23. There was a strong correlation between presence of an NSD1 alteration and clinical phenotype, in that 28 of 37 (76%) patients in group 1 had NSD1 mutations or deletions, whereas none of the patients in group 4 had abnormalities of NSD1. Three patients with Weaver syndrome had NSD1 mutations, all between amino acids 2142 and 2184. We conclude that intragenic mutations of NSD1 are the major cause of Sotos syndrome and account for some Weaver syndrome cases but rarely occur in other childhood overgrowth phenotypes.

Figure 1

Typical facial phenotype in overgrowth groups 1, 2, and 3. A, Group 1 (classic facial gestalt of Sotos syndrome). B, Group 2 (patients with similarities to Sotos syndrome but with some atypical characteristics; primarily the facial features were not classical). C, Group 3 (Weaver syndrome). Patients in Group 4 did not have a distinctive facial phenotype but were characterized by not having the facial phenotypes present in the other three groups.

Figure 2

NSD1 deletions in three patients with childhood overgrowth—COG25, COG44, and COG70. A, Marker allele haplotypes for nine microsatellite markers spanning NSD1, demonstrating maternal deletion in COG25, probable paternal deletion in COG44, and deletion of unknown origin in COG70. B, Fluorescent multiplex PCR demonstrating a 0.5 reduction of NSD1 exons relative to MLH1, in COG25, COG44, and COG70, and a normal ratio in two control samples: (1) the mother of COG25 and (2) COG33 (who has an intragenic NSD1 mutation). The Y-axis shows fluorescence (in arbitrary units), and the X-axis indicates the size (in bp).

Figure 3

Schematic representation of NSD1, showing the distribution of intragenic mutations identified in the present study and the associated phenotype. Exons of NSD1 are shown as boxes with the exon number underneath. Functional domains of NSD1 are shown as shaded boxes, with the domain name above. Mutations are shown as triangles, with truncating mutations (insertions, deletions, nonsense, and splice-site) above the gene and missense mutations below the gene. One mutation (R604X) was identified twice and is depicted as two triangles, one above the other.

Figure 4

NSD1 missense mutations in patients with childhood overgrowth. Residues altered by missense mutations are shown in red boxes. Consensus residues in the PHD and SAC domains are shown in black boxes. Conserved residues in NSD1, mouse Nsd1, NSD2, and NSD3 are shown in shaded boxes. A, The alignment of five PHD domains in NSD1 and the position of the missense mutations identified in the present study. B, Missense mutations in PWWPII, SAC, SET, and C/H-rich domains and in corresponding regions in mouse Nsd1, NSD2, and NSD3.