The SOX5 gene encodes a transcription factor involved in the regulation of nervous system development and chondrogenesis. This article reports on two cases of 12p12.1 deletion involving SOX5 presenting with global developmental delay, intellectual disability, expressive language delay, mild motor impairment, distinct features, and multiorgan involvement. The first case involves a 32-month-old boy with de novo 53-kilobase interstitial deletion at 12p12.1, representing the smallest deletion reported, and presents with severe symptomatology. The second case is a 31-month-old girl with 3.2-megabase deletion at 12p12.2 p12.1 with severe neurodevelopmental disability and minimal organ involvement. These patients bear many of the characteristics previously reported in patients with SOX5 mutations. We propose a neurodevelopmental approach to a novel syndrome with dose- and location-sensitive SOX5 gene expression.
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