Prenatal Diagnosis of Myhre Syndrome in Two Cases: Further Delineation of the Cardiac and External Phenotype

Myhre syndrome is a rare genetic disease caused by recurrent gain-of-function variants in SMAD4 (Ile500Thr, Ile500Val, Arg496Cys, and Ile500Met) characterized by postnatal short stature with pseudo-muscular build, joint stiffness, variable intellectual disability, hearing loss, and a distinctive pattern of dysmorphic facial features. The course can be severe in some cases, with life-threatening cardiac and pulmonary complications caused by connective tissue involvement. These progressive features over time make early clinical diagnosis difficult but possible by astute clinicians who evaluate young children with autism or short stature and unusual appearance. Only two cases of Myhre syndrome diagnosed during the prenatal period have been reported. Here, we present a detailed description of two unrelated fetuses with Myhre syndrome, each molecularly confirmed by genome or exome sequencing, who underwent fetal examination after termination of pregnancy. One had severe intrauterine growth retardation associated with crossed fused renal ectopia, and the other one had pulmonary atresia with ventricular septal defect (a form of tetralogy of Fallot). Both had mild dysmorphic features with a wide nasofrontal angle. Our results and a systematic prenatal literature review add insight into the early natural history of Myhre syndrome and highlight the contribution of prenatal next-generation sequencing in prenatal diagnosis and the importance of fetal autopsy in Myhre syndrome.