Destabilized SMC5/6 complex leads to chromosome breakage syndrome with severe lung disease

Area of Science:

• Genetics
• Molecular Biology
• Immunology

Background:

• Structural Maintenance of Chromosomes (SMC) proteins are crucial for genomic stability, DNA repair, and cell division.
• Defects in chromosome maintenance are associated with rare chromosome breakage disorders.

Purpose of the Study:

• To identify the genetic cause of a severe chromosome breakage syndrome presenting with early childhood lung disease and immunodeficiency.
• To investigate the functional consequences of identified mutations on the SMC5/6 complex and cellular processes.

Main Methods:

• Whole exome sequencing was performed on affected individuals from two kindreds.
• Functional studies were conducted on patient-derived cells to assess DNA damage response, homologous recombination, and SMC5/6 complex integrity.

Main Results:

• Biallelic missense mutations in the NSMCE3 gene were identified as the cause of the syndrome.
• NSMCE3 mutations destabilized the SMC5/6 complex, leading to chromosome rearrangements, micronuclei, and impaired homologous recombination.
• Patient cells exhibited sensitivity to replication stress and DNA damage.

Conclusions:

• This study links missense mutations in NSMCE3 to an autosomal recessive chromosome breakage syndrome.
• The syndrome is characterized by combined T and B cell immunodeficiency and acute respiratory distress syndrome in early childhood.
• Defective NSMCE3 function disrupts the SMC5/6 complex, impairing DNA repair and leading to genomic instability.