First Identification of Rare Exonic and Deep Intronic Splice-Altering Variants in Patients With...

Area of Science:

• Genetics
• Molecular Biology
• Neurology

Background:

• Sarcoglycanopathies and dystrophinopathies present diagnostic challenges due to complex genetic variants.
• Routine genomic detection often fails to identify pathogenic non-coding or structural variants in DMD or sarcoglycan genes.

Purpose of the Study:

• To achieve precise genetic diagnosis for three patients from two families with suspected sarcoglycanopathy or dystrophinopathy.
• To investigate cases where standard genetic testing was inconclusive.

Main Methods:

• Utilized muscle-derived reverse transcription-polymerase chain reaction (RT-PCR) and TA cloning to detect aberrant transcripts.
• Performed genomic Sanger sequencing around aberrant transcripts to identify splice-altering variants.
• Conducted bioinformatic and segregation analyses for detected variants.

Main Results:

• Identified novel compound heterozygous variants in the SGCB gene in two patients, including deep intronic splice-altering variants (DISVs) causing pseudoexon activation and partial intron inclusion.
• Discovered a novel DISV and a nonsense variant in SGCB in another patient, with the nonsense variant unexpectedly creating a new splice site leading to exon deletion.

Conclusions:

• This study reports the first identification of rare exonic and deep intronic splice-altering variants (DISVs) in the SGCB gene.
• These findings advance the genetic diagnosis of sarcoglycanopathies by highlighting the importance of investigating complex intronic variants.