Novel Marfan Syndrome-Associated Mutation in the FBN1 Gene Caused by Parental Mosaicism and Leading to Abnormal Limb Patterning

Marfan syndrome is an autosomal dominant disorder of the connective tissue caused by mutations in the fibrillin-1 (FBN1) gene. Mutations affecting cysteine residues within the epidermal growith factor-like calcium-binding domains (EGF_CA) of FBN1 are associated with Marfan syndrome features and, especially, with ectopia lentis. We report a novel substitution, affecting the first cysteine of an EGF_CA-binding module encoded by exon 63 of FBN1 (C2571Y), in a patient presenting with typical Marfan syndrome features but without ectopia lentis. The involvement of this particular carboxi-terminal domain in bone morphogenetic protein signaling is evidenced by patterning defects in the apendicular skeleton shown by the gain of a phalange at digit 1 and the fusion of some wrist bones. Although the mutation appeared as sporadic, detailed analysis revealed that the asymptomatic father was a gonosomal mosaic, and that aproximately 25% of his body cells carry the mutation. Based on this and previous evidence on the origin of sporadic mutations, we would like to stress the importance of detailed parental genetic screening, so the risk of recurrence may be evaluated.