Mutations in the FBN1 gene cause Marfan syndrome (MFS) and have been associated 
with a wide range of milder overlapping phenotypes. A proportion of patients 
carrying a FBN1 mutation does not meet diagnostic criteria for MFS, and are 
diagnosed with "other type I fibrillinopathy." In order to better describe this 
entity, we analyzed a subgroup of 146 out of 689 adult propositi with incomplete 
"clinical" international criteria (Ghent nosology) from a large collaborative 
international study including 1,009 propositi with a pathogenic FBN1 mutation. 
We focused on patients with only one major clinical criterion, [including 
isolated ectopia lentis (EL; 12 patients), isolated ascending aortic dilatation 
(17 patients), and isolated major skeletal manifestations (1 patient)] or with 
no major criterion but only minor criteria in 1 or more organ systems (16 
patients). At least one component of the Ghent nosology, insufficient alone to 
make a minor criterion, was found in the majority of patients with isolated 
ascending aortic dilatation and isolated EL. In patients with isolated EL, 
missense mutations involving a cysteine were predominant, mutations in exons 
24-32 were underrepresented, and no mutations leading to a premature truncation 
were found. Studies of recurrent mutations and affected family members of 
propositi with only one major clinical criterion argue for a clinical continuum 
between such phenotypes and classical MFS. Using strict definitions, we conclude 
that patients with FBN1 mutation and only one major clinical criterion or with 
only minor clinical criteria of one or more organ system do exist but represent 
only 5% of the adult cohort.