Genome rearrangements in patients with blepharophimosis, mental retardation and hypothyroidism, so-called Young-Simpson syndrome

Deficiency for the ubiquitin ligase UBE3B in a blepharophimosis-ptosis-intellectual-disability syndrome

Ubiquitination plays a crucial role in neurodevelopment as exemplified by Angelman syndrome, which is caused by genetic alterations of the ubiquitin ligase-encoding UBE3A gene. Although the function of UBE3A has been widely studied, little is known about its paralog UBE3B. By using exome and capillary sequencing, we here identify biallelic UBE3B mutations in four patients from three unrelated families presenting an autosomal-recessive blepharophimosis-ptosis-intellectual-disability syndrome characterized by developmental delay, growth retardation with a small head circumference, facial dysmorphisms, and low cholesterol levels. UBE3B encodes an uncharacterized E3 ubiquitin ligase. The identified UBE3B variants include one frameshift and two splice-site mutations as well as a missense substitution affecting the highly conserved HECT domain. Disruption of mouse Ube3b leads to reduced viability and recapitulates key aspects of the human disorder, such as reduced weight and brain size and a downregulation of cholesterol synthesis. We establish that the probable Caenorhabditis elegans ortholog of UBE3B, oxi-1, functions in the ubiquitin/proteasome system in vivo and is especially required under oxidative stress conditions. Our data reveal the pleiotropic effects of UBE3B deficiency and reinforce the physiological importance of ubiquitination in neuronal development and function in mammals.

Blepharophimosis mental retardation syndrome Say-Barber/Biesecker/Young-Simpson type - new findings with neuroimaging

We report on a female patient with blepharophimosis mental retardation syndrome of Say/Barber/Biesecker/Young-Simpson (SBBYS) type. Main findings in her were marked developmental delay, blepharophimosis, ptosis, cleft palate, external auditory canal stenosis, small and malformed teeth, hypothyroidism, hearing impairment, and joint limitations. We performed diffusion tensor magnetic resonance imaging (MRI) and tractography of the brain which showed inappropriate myelination and disturbed white matter integrity. Cytogenetic analysis, subtelomeric fluorescence in situ hybridization and comparative genomic hybridization failed to identify an abnormality. It remains uncertain whether the MRI findings are specific to the present patient or form part of the SBBYS syndrome.

The difficult nosology of blepharophimosis-mental retardation syndromes: report on two siblings

Blepharophimosis-mental retardation syndromes (BMRS) include a group of clinically and etiologically heterogeneous conditions, which can occur as isolated features or as part of distinct disorders displaying multiple congenital anomalies. We report on two siblings, a 6-year-old girl and an 18-month-old male, presenting with overlapping clinical findings. Major characteristics included facial dysmorphisms with upward slanted palpebral fissures, blepharophimosis, telecanthus, hypertelorism, posteriorly rotated and abnormal ears, and micrognathia. Ectodermal abnormalities consisted of fine hair, sparse eyebrows, and thin skin. Both patients had feeding difficulties with gastro-esophageal reflux and growth retardation. Psychomotor skills were severely delayed with no verbal capacity. The male sib also displayed low growth hormone (GH) levels, while the older sister had low cholesterol and mildly elevated TSH levels. Numerous metabolic/genetic investigations, including cholesterol precursors, dosage, and high-resolution array-CGH, were negative. BMR syndromes, including Dubowitz syndrome, Marden-Walker syndrome, Ohdo/Ohdo-like syndromes, and the cholesterol storage disorders were considered. We concluded that these two patients are affected by a possible autosomal recessive condition within the heterogeneous clinical spectrum of BMRS, fitting with the Young-Simpson syndrome subtype.