Hyperphagia, mild developmental delay but apparently no structural brain anomalies in a boy without SOX3 expression.

The transcription factor SOX3 is widely expressed in early vertebrate brain development. In humans, duplication of SOX3 and polyalanine expansions at its C-terminus may cause intellectual disability and hypopituitarism. Sox3 knock-out mice show a variable phenotype including structural and functional anomalies affecting the branchial arches and midline cerebral structures such as the optic chiasm and the hypothalamo-pituitary axis. SOX3 is claimed to be required in normal brain development and function in mice and humans, as well as in pituitary and craniofacial development. We report on an 8-year-old boy with a 2.1 Mb deletion in Xq27.1q27.2, which was found to be inherited from his healthy mother. To our knowledge, this is the smallest deletion including the entire SOX3 gene in a male reported to date. He is mildly intellectually disabled with language delay, dysarthria, behavior problems, minor facial anomalies, and hyperphagia. Hormone levels including growth, adrenocorticotropic and thyroid stimulating hormones are normal. Magnetic resonance imaging (MRI) at age 6 years showed no obvious brain anomalies. Genetic redundancy between the three members of the B1 subfamily of SOX proteins during early human brain development likely explains the apparently normal development of brain structures in our patient who is nullisomic for SOX3.

Haploinsufficiency of two histone modifier genes on 6p22.3, ATXN1 and JARID2, is associated with intellectual disability.

BACKGROUND: Nineteen patients with deletions in chromosome 6p22-p24 have been published so far. The syndromic phenotype is varied, and includes intellectual disability, behavioural abnormalities, dysmorphic features and structural organ defects. Heterogeneous deletion breakpoints and sizes (1-17 Mb) and overlapping phenotypes have made the identification of the disease causing genes challenging. We suggest JARID2 and ATXN1, both harbored in 6p22.3, as disease causing genes. METHODS AND RESULTS: We describe five unrelated patients with de novo deletions (0.1-4.8 Mb in size) in chromosome 6p22.3-p24.1 detected by aCGH in a cohort of approximately 3600 patients ascertained for neurodevelopmental disorders. Two patients (Patients 4 and 5) carried non-overlapping deletions that were encompassed by the deletions of the remaining three patients (Patients 1-3), indicating the existence of two distinct dosage sensitive genes responsible for impaired cognitive function in 6p22.3 deletion-patients. The smallest region of overlap (SRO I) in Patients 1-4 (189 kb) included the genes JARID2 and DTNBP1, while SRO II in Patients 1-3 and 5 (116 kb) contained GMPR and ATXN1. Patients with deletion of SRO I manifested variable degrees of cognitive impairment, gait disturbance and distinct, similar facial dysmorphic features (prominent supraorbital ridges, deep set eyes, dark infraorbital circles and midface hypoplasia) that might be ascribed to the haploinsufficiency of JARID2. Patients with deletion of SRO II showed intellectual disability and behavioural abnormalities, likely to be caused by the deletion of ATXN1. Patients 1-3 presented with lower cognitive function than Patients 4 and 5, possibly due to the concomitant haploinsufficiency of both ATXN1 and JARID2. The chromatin modifier genes ATXN1 and JARID2 are likely candidates contributing to the clinical phenotype in 6p22-p24 deletion-patients. Both genes exert their effect on the Notch signalling pathway, which plays an important role in several developmental processes. CONCLUSIONS: Patients carrying JARID2 deletion manifested with cognitive impairment, gait disturbance and a characteristic facial appearance, whereas patients with deletion of ATXN1 seemed to be characterized by intellectual disability and behavioural abnormalities. Due to the characteristic facial appearance, JARID2 haploinsufficiency might represent a clinically recognizable neurodevelopmental syndrome.