Any of the following findings in an FBN1 screening should be considered causal in making the diagnosis of Marfan syndrome. Marfan syndrome has been positively associated with each of the following:

• Mutation previously shown to segregate in Marfan family
• De novo (with proven paternity and absence of disease in parents) mutation (one of the five following categories)
• Nonsense mutation
• Inframe and out of frame deletion/insertion
• Splice site mutations affecting canonical splice sequence or shown to alter splicing on mRNA/cDNA level
• Missense affecting/creating cysteine residues
• Missense affecting conserved residues of the EGF consensus sequence ((D/N)X(D/N)(E/Q)Xm(D/N)Xn(Y/F) with m and n representing variable number of residues; D aspartic acid, N asparagine, E glutamic acid, Q glutamine, Y tyrosine, F phenylalanine)
• Other missense mutations: segregation in family if possible + absence in 400 ethnically matched control chromosomes, if no family history absence in 400 ethnically matched control chromosomes
• Linkage of haplotype for n≥6 meioses to the FBN1 locus