Epidemiology and natural history in 101 subjects with FKRP-related limb-girdle muscular dystrophy R9. The Norwegian LGMDR9 cohort study (2020).

We aimed to investigate the epidemiology and natural history of FKRP-related limb-girdle muscular dystrophy R9 (LGMDR9) in Norway. We identified 153 genetically confirmed subjects making the overall prevalence 2.84/100,000, the highest reported figure worldwide. Of the 153 subjects, 134 (88 %) were homozygous for FKRP c.826C>A giving a carrier frequency for this variant of 1/101 in Norway. Clinical questionnaires and patient notes from 101 subjects, including 88 c.826C>A homozygotes, were reviewed, and 43/101 subjects examined clinically. Age of onset in c.826C>A homozygotes demonstrated a bimodal distribution. Female subjects showed an increased cumulative probability of wheelchair dependency and need for ventilatory support. Across the cohort, the need for ventilatory support preceded wheelchair dependency in one third of the cases, usually due to sleep apnea. In c.826C>A homozygotes, occurrence of cardiomyopathy correlated positively with male gender but not with age or disease stage. This study highlights novel gender differences in both loss of ambulation, need for ventilatory support and the development of cardiomyopathy. Our results confirm the need for vigilance in order to detect respiratory insufficiency and cardiac involvement, but indicate that these events affect males and females differently.