Autosomal Dominant Missense DAG1 Variant Linked to Mild-Moderate LGMD R16

Limb-girdle muscular dystrophies (LGMDs) are disorders with an important clinical heterogeneity, usually involving proximal limb muscles. One subtype, LGMD R16 (LGMD 2P), is an autosomal recessive condition caused by pathogenic variants in DAG1, with clinical presentations ranging from mild to extremely severe forms. DAG1 is responsible for producing dystroglycan, an essential complex in the muscular protein network. Following translation, dystroglycan is cleaved into alpha-dystroglycan, which undergoes glycosylation and acts as a sarcolemmal receptor for extracellular proteins, and beta-dystroglycan, which connects to dystrophin. In recent years, heterozygous nonsense or frameshift DAG1 variants have been linked with asymptomatic hyperCKemia (increased serum creatine kinase levels) or mild muscular phenotypes characterized by fatigability and myalgia. Here, we describe a Romanian family comprising four affected individuals (one father and three sons) carrying the heterozygous missense DAG1 variant NM_004393.6:c.887G>A, NP_004384.5:p.(Gly296Asp) and showing a mild-moderate muscular phenotype similar to previous cases of DAG1 haploinsufficiency. Three of the affected individuals exhibit myopathic changes in muscle biopsies (increased fiber size variability, internalized nuclei, and regenerating fibers), while two demonstrate reduced alpha-dystroglycan glycosylation in muscle tissue. Atomic force microscopy findings in myoblasts from one patient showed a significantly lower stiffness compared to controls. These findings align with prior reports and further support the pathogenicity of this variant.