Mutations in TUBB4B Cause a Distinctive Sensorineural Disease.

Area of Science:

• Genetics
• Neurobiology
• Cell Biology

Background:

• Leber congenital amaurosis (LCA) is a severe inherited retinal disease causing early-onset blindness.
• LCA is typically linked to photoreceptor dysfunction, but syndromic forms exist.
• Microtubules (MTs) are crucial cytoskeletal components involved in cellular structure and function.

Purpose of the Study:

• To investigate the genetic basis of an atypical LCA presentation with early-onset hearing loss.
• To identify novel genes and understand the molecular mechanisms underlying syndromic LCA.
• To explore the role of beta-tubulin 4B isotype (TUBB4B) in LCA pathogenesis.

Main Methods:

• Exome sequencing was performed on a multiplex family and simplex cases with LCA and hearing loss.
• Structural analysis of the identified TUBB4B mutations.
• Functional studies using cell culture (overexpression) and patient-derived fibroblasts to assess MT dynamics.

Main Results:

• Two heterozygous mutations in TUBB4B, affecting Arg391, were identified in affected individuals.
• The Arg391 residue is critical for MT stability through interaction with alpha-tubulin.
• Mutant TUBB4B assembled into MTs but significantly altered MT growth dynamics.

Conclusions:

• This study identifies TUBB4B mutations as a cause of syndromic LCA associated with hearing loss.
• The findings establish a link between sensorineural diseases and aberrant MT behavior.
• This LCA form is unrelated to known ciliary dysfunction, highlighting novel pathogenic pathways.