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Objective: Filamin-A (FlnA) is the first identified gene for non-syndromic mitral valve dystrophy, located on the X chromosome. We aim to describe, by using echocardiography, the overall mitral valve phenotype in male and female patients from a large P637Q FlnA mutation family.Methods: Thirty-six patients over 10 year old (41±16 years, 12 males) with the P637Q FlnA mutation were matched with 18 control subjects. Six additional patients with the P637Q FlnA mutation under 10 year old were also examined.Results: In male patients both anterior (AL) and posterior (PL) mitral leaflets were significantly elongated (AL: 25.1±3.2 vs 21.6±2.8 mm in controls, P=0.03; PL: 17.8±3.9 vs 12.3±0.9 mm, P=0.001), thickened (leaflets basal to tip segments: 2.6±0.7 to 3.7±1.1 vs 1.6±0.3 to 1.8±0.4 mm, P= 0.001 to 0.0002) and moderately billowed in the left atrium relative to the annulus line (AL: -1.1±3.4 vs +3.2±2.2 mm, P= 0.0008; PL: -2.6±2.5 vs +4.0±2.7 mm, P= 0.0001). Anterior and posterior chordal lengths did not differ significantly between male patients and controls but both anterior (APM) and posterior (PPM) papillary muscles were positioned closer to the mitral annulus as assessed by the mitral annulus-PM distance to the LV long axis length ratio (APM: 27±5 vs 34±4%, P=0.01; PPM: 28±8 vs 34±3%, P=0.03). In female patients lesions were minored as expected in an X-linked disease. Mitral annulus enlargement was present in males but not in females patients. No chordal rupture was seen in any patient. In male and female patients the phenotype of mitral valve dystrophy is unique associating also a doming aspect in diastole with a restrictive motion predominant on the posterior leaflet in females. Finally, mitral valves lesions were also clearly identified in younger patients (3 to 7 year old) particularly in males .Conclusions: X-linked P637Q FlnA mutation elicits unique mitral valve dystrophy. The phenotype associates mitral leaflet elongation, thickening and billowing in male patients with a moderate diastolic doming aspect or restrictive motion, predominant on the posterior leaflet in females. Papillary muscle position is displaced closer to the mitral annulus in relation to mitral valve apparatus development alteration.