Abstract Three boys aged 7-13 months visited the hospital due to unusual facies (prominent forehead, hypertelorism, or long mandible), motor developmental delay, and mental retardation. As for body length and head circumference, only one patient had a head circumference of > 2 SD. Two patients had an advanced bone age, one had electroencephalographic abnormalities, and 3 had enlarged ventricles on head CT. The whole-genome microarray analysis showed the deletion of a copy with a size of 1.75 Mb in the chromosomal region 5q35.2 in one patient, which contained the NSD1 gene. Quantitative real-time PCR was performed for the validation of the region with copy number variation, and the results showed that the copy number of the NSD1 gene in this patient was reduced by half. High-throughput sequencing identified two heterozygous mutations, c.1157T > G and c.1177G > T, in the NSD1 gene in two patients. c.1157T > G mutations had not been reported before, but the bioinformatics analysis showed that this mutation had pathogenicity. All three boys were diagnosed with Sotos syndrome. Sotos syndrome is a congenital overgrowth syndrome with autosomal dominant inheritance; 70%-90% of patients have NSD1 gene mutations, and about 10% of patients have depletion in the 5q35 region (containing the NSD1 gene).
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