Marshall-Smith syndrome: Novel pathogenic variant and previously unreported associations with precocious puberty and aortic root dilatation.

Marshall-Smith Syndrome (MRSHSS) is a very rare genetic disorder characterized by failure to thrive and characteristic dysmorphic features associated with accelerated osseous maturation. We present a nine-year-old girl who was diagnosed with MRSHSS based on characteristic clinical features supported by the identification of a novel de novo pathogenic variant in the NFIX gene. The patient also presented with precocious puberty diagnosed at five years of age and had an abnormal GnRH stimulation test indicative of central precocious puberty. Central precocious puberty has not been described in association with MRSHSS previously in the medical literature and broadens our knowledge of the natural history of MRSHSS. The causes of advanced bone age in this syndrome are also reviewed. Additionally, the patient showed progressive dilatation of the aortic root. Although connective tissue abnormalities have been described in association with MRSHSS, aortic root dilatation has not. Understanding the mechanism of comorbidities such as advanced bone age and aortic root dilatation in MRSHSS patients enables future development of anticipatory guidance, preventative care measures, and treatment guidelines.