A newly recognized 13q12.3 microdeletion syndrome characterized by intellectual disability, microcephaly, and eczema/atopic dermatitis encompassing the HMGB1 and KATNAL1 genes.

Proximal deletions of the long arm of chromosome 13 have been reported only rarely. Here we present three unrelated patients with heterozygous, apparently de novo deletions encompassing 13q12.3. The patients present with moderate demonstrated or apparent intellectual disability, postnatal microcephaly, and eczema/atopic dermatitis as the predominant symptoms. In addition, they had pronounced feeding difficulties in early infancy. They displayed similar facial features such as malar flattening, a prominent nose with underdeveloped alae nasi, a smooth philtrum, and a thin vermillion of the upper lip. The proximal and distal breakpoints were clustered and the deletions spanned from 1.4 to 1.7 Mb, comprising at least 11 RefSeq genes. However, heterozygous deletions partially overlapping those observed in the present patients have been described in healthy parents of patients with Peters-Plus syndrome, an autosomal recessive disorder caused by inactivation of the B3GALTL gene. We therefore propose that the critical region of the 13q12.3 microdeletion syndrome contains only three genes, namely, KATNAL1, HMGB1, and LINC00426, a non-protein coding RNA. The KATNAL1 protein belongs to a family of microtubule severing enzymes that have been implicated in CNS plasticity in experimental models, but little is known about its function in humans. The HMGB1 protein is an evolutionarily conserved chromatin-associated protein involved in many biologically important processes. In summary, we propose that microdeletion 13q12.3 represents a novel clinically recognizable condition and that the microtubule severing gene KATNAL1 and the chromatin-associated gene HMGB1 are candidate genes for intellectual disability inherited in an autosomal dominant pattern.

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