Out-of-frame Translation Rescues a Loss-of-function Variant in a Novel TBCE Phenotype

Area of Science:

• Genetics and Molecular Biology
• Neurodevelopmental Disorders
• Protein Biochemistry

Background:

• Pathogenic variants in the Tubulin-Specific Chaperone E (TBCE) gene are associated with severe neurodevelopmental disorders.
• These disorders include Hypoparathyroidism-retardation-dysmorphism (HRD) syndrome, Kenny-Caffey syndrome type 1, and progressive encephalopathy with amyotrophy and optic atrophy.

Purpose of the Study:

• To identify and characterize a novel, milder phenotype associated with TBCE gene variants.
• To elucidate the clinical and molecular mechanisms underlying this new TBCE-related disorder.

Main Methods:

• Deep next-generation sequencing (NGS) for splicing analysis.
• Western blotting for TBCE detection and luciferase reporter assays for translation efficiency.
• Immunofluorescence microscopy, microtubule dynamics studies, and electron microscopy for cellular and ultrastructural analysis.

Main Results:

• Seven patients presented with a milder phenotype including amyotrophy, testicular failure, and mild intellectual disability, associated with the NM_003193.5:c.100+1G>A variant.
• The c.100+1G>A variant causes splicing alterations but leads to a partially functional TBCE protein via alternative open reading frame translation.
• Cellular analysis revealed reduced Golgi compactness and acto-myosin degradation, but normal microtubule dynamics.

Conclusions:

• Complex molecular mechanisms, including alternative translation, contribute to the milder TBCE-associated phenotype.
• This study identifies a new TBCE-related disorder and suggests potential underdiagnosis, particularly in Slavic populations, due to the variant's frequency.