Using four patient registries, one study was able to identify all patients (153) in Norway with genetically confirmed FKRP-related LGMD R9. The estimated disease prevalence for the country is 2.84/100,000 in the general population (the highest known to date), with 1.98/100,000 in the paediatric population and 3.06/100,000 in the adult population.
A study of the clinical and genetic data of 101 of them reveals that :
- 87.6% are carriers of the homozygous c.826C>A mutation;
- the age of onset of the disease in these patients is divided into two groups: one predominant (75% of the group) at an average of seven years of age and the other around 29 years of age.
- Lower limb weakness and exercise intolerance were the most common initial symptoms, and some patients showed gross motor developmental abnormalities as early as the first year of life.
Statistical analyses of the homozygous c.826C>A group show that, unlike other LGMD (R1, R7, R12…), in LGMD R9 :
- women have a higher probability of being wheelchair dependent (50% at age 49 vs. 20% in men);
- women have a higher probability of needing ventilatory assistance (50% at 52 years old vs. 21% in men).
Finally, cardiomyopathy tends to be more common in men (50% probability at age 55 vs 25% in women). As in other studies, the development of cardiomyopathy is not correlated with loss of mobility, duration of disease or age of the patient.
