Noonan syndrome and type 1 Chiari malformation: Possible association.

Noonan syndrome (NS) is mostly an autosomal dominant genetic disorder that affects between 1 in 1000 and 1 in 2500 people. Type 1 Chiari malformations (CM1) have an estimated prevalence of <1 in 1000 people. Though NS typically spares the posterior fossa, there have been 11 past instances of patients with NS having a concurrent CM1 that have been published in the literature. Each of these 11 cases occurred sporadically, in an isolated individual with no published family history of CM1. This case report presents a three generational family with four members having both NS and concurrent CM1. All affected family members share a pathogenic variant in PTPN11. A literature review was performed to identify and compile data regarding all past published cases of NS and CM1 occurring concurrently. Since 1982, a dozen case reports have detailed NS with concurrent CM1. Where molecular genetic data was presented, seven had a variant in PTPN11, and only one had a variant in another gene. The clustering of NS with CM1 within a single family that shares the same genotype, along with the exclusion of both NS and CM1 in other family members, may indicate that CM1 is a part of the NS phenotype.