Background and Objective: Previously, the coincidence of two different disease phenotypes in a single patient was considered to be a new phenotype or a phenotypic extension of a single known disease. However, with the advent of whole exome sequencing, it has become clear that in many cases it is a new phenotype or phenotypic extension. This case report represents a blended phenotype of Marfan and Larsen syndrome. Up to the time of reporting this case, we could not find a similar case in the sources.
Case Report: A full-term male infant delivered vaginally by a primi-mother in a non-consanguineous marriage was transferred to the intensive care unit because of respiratory distress, meningomyelocele and dysmorphism. On clinical examination, the baby had a heart murmur. The baby required oxygen support but no pressure. We slowly weaned off oxygen and gradually started feeding. An ultrasound and echocardiography were performed to rule out malformations. Using molecular and next-generation exome sequencing techniques, the infant was found to have heterozygous variations of the FBN1 gene c.6094A>T p.Thr2032Ser (depth -36x), a novel variant, and the FLNB gene c.2956C>Tp.Arg986Trp (depth -48x), suggesting for neonatal Marfan syndrome (nMFS) and Larsen syndrome phenotype,  which was compatible with the phenotypic findings of the neonate. Unfortunately, the infant died because of sepsis and aspiration.
Conclusion: In extremely rare cases, there may be more than one syndrome. Under these circumstances, the prognosis is grim, as usual. When the syndromic phenotype varies, advanced genetic testing is preferred.