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Defining Haplosufficiency in Autosomal Recessive Limb-Girdle Muscular Dystrophy Using Molecular Markers in Disease
Alison Gaynor1,2, Dove Enicks1,2, Katherine Karam1,2
1Center for Inherited Myology Research, Virginia Commonwealth University, Richmond; and.
Neurology. Genetics
|July 15, 2026
Summary
Haplosufficient carriers of limb-girdle muscular dystrophy (LGMD) show reduced protein levels but maintain normal strength. This suggests a protein expression threshold for haplosufficiency, crucial for gene therapy strategies.
Area of Science:
- Genetics
- Molecular Biology
- Neuromuscular Disorders
Background:
- Autosomal recessive limb-girdle muscular dystrophies (LGMD) result from biallelic loss-of-function variants.
- Haplosufficient carriers are presumed to have adequate protein expression for normal physical function.
Purpose of the Study:
- To quantify relative protein expression in carriers of LGMD subtypes R1 (CAPN3), R9 (FKRP), and R3 (SGCA).
- To assess the enzymatic functionality of FKRP in LGMDR9 carriers.
- To establish a potential protein expression threshold for haplosufficiency.
Main Methods:
- Muscle biopsies from affected individuals and carriers of LGMDR1, LGMDR9, and LGMDR3.
- RNA-sequencing (RNA-seq) for gene expression analysis.
- Western blotting for relative protein quantification.
Main Results:
- LGMDR1 carriers had ~25% calpain-3 expression; LGMDR9 carriers showed ~50% FKRP functionality.
- LGMDR3 carriers displayed normal α- and β-sarcoglycan levels.
- Reduced protein expression and functionality were observed in carriers compared to controls.
Conclusions:
- Haplosufficient LGMD carriers exhibit reduced but functional protein levels.
- This level of protein expression may define the threshold for successful gene replacement therapy.
- Findings provide insights into LGMD pathophysiology and therapeutic targets.
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