The phenotypic variability is known in myopathies related to collagen-VI (COL6-RD), although the cause is not clearly understood. Recently it has been published a parental mosaicism in dominant negative mutations as a cause of intra-familial phenotypic variability. We identified a family with a novel mutation in COL6A1 gene as a cause for inter-generational and intra-generational phenotypic heterogeneity. We describe a non-consanguineous family with affected mother and two siblings. We present the clinical phenotype, muscle imaging, molecular study and expression of collagen IV in muscle and skin fibroblasts. The clinical phenotype is suitable for COL6-RD in the three patients: muscle weakness, joint contractures, joint hyperlaxity, keloid scar formation, scoliosis and respiratory insufficiency. The family displays a striking intra-generational and inter-generational phenotypic heterogeneity, where the phenotype is intermediate in the mother (wheelchair at thirties, moderate respiratory insufficiency), mild in the daughter (proximal weakness, independent gait, no respiratory involvement), and very severe with congenital onset in the son (severe contractures at birth, wheelchair at age of 8, severe respiratory involvement). The pattern of collagen VI expression in skin fibroblast was according to the phenotype severity. We identify the novel heterozygote mutation p.Gly263Asp in COL6A1 gene, which segregate with the disease. We report the phenomenon of intra-generational phenotypic variability in COL6-RD. A parental mosaicism may explain the inter-generational variability but not the intra-generational one. Our family harbors a novel mutation in COL6A1 gene so the clinical variability could be associated to this new mutation.