Novel MNX1 mutations and clinical analysis of familial and sporadic Currarino cases

Currarino Syndrome (CS) is a rare congenital malformation characterized by three major clinical aspects: sacral anomalies, anorectal malformation and presacral mass. In familial settings the disorder is transmitted as autosomal dominant trait, with a wide phenotype variability and low penetrance. The causative gene of CS is the motor neuron and pancreas homeobox-1 (MNX1), mapped at 7q36, and coding for a transcription factor. Mutations in the MNX1 have been implicated in almost all familial but only in 30% of sporadic cases. In our cohort of 28 CS cases, 8 were familiar, 18 were sporadic and 2 were not determined cases. We performed mutational analysis of MNX1 in all cases by DNA sequencing as well as by Multiplex Ligation-dependent Probe Amplification (MLPA) in those CS cases where no MNX1 mutations were found, to exclude a MNX1 heterozygous loss. We identified 10 novel and 4 recurrent mutations. Among the novel mutations, 2 were frameshift variants (p.Ser4IlefsX52, p.Phe248SerfsX35), 6 were missense variants (p.Pro27Leu, p.Gly103Arg, p.Leu254Pro, p.Leu278Pro, p.Glu282Lys, p.Arg292Gly), one was a non-sense variant (p.Lys297X), and the last one was a synonymous variant (p.Gln290Gln). Mutated patients showed a variability of phenotypes but all share at least the association of sacral agenesis and presacral mass, and this co-occurrence can constitute a pathognomonic sign to perform MNX1 analysis. Genetic heterogeneity could be a possible explanation for some of the sporadic not mutated patients even if a mis-diagnosis could not be excluded. Finally, we provide an up-date of the more recent literature, reporting a total number of 82 MNX1-CS related mutations.