Incidence of SCN-Assoicated Gene Mutations in Severe Congenital Neutropenia Patients in North America

Severe congenital neutropenia is a genetically heterogeneous syndrome associated with mutations in several different genes including ELA2, HAX1, GFI1, WAS, and CSF3R. The goal of this study was to define the mutation frequency of these genes in the North American SCN patient population. We also sequenced SBDS, since mutations of SBDS have been associated with congenital and acquired neutropenia. A total of 159 patients were identified in the North American Severe Chronic Neutropenia International Registry (SCNIR) for whom informed consent and genomic DNA samples adequate for sequencing were available. To accommodate our semi-automated high-throughput sequencing pipeline, 94 samples were chosen for sequencing. Since ELA2 sequencing had already been performed in most cases, preference was given to those samples without known ELA2 mutation. Among the samples, 73 were from patients with SCN, 4 with cyclic neutropenia, 10 with idiopathic neutropenia, 2 with Shwachman-Diamond Syndrome (SDS), and 3 with Barth syndrome. Two samples were excluded because of poor sequence quality. Singleton cases with validated mutations of GFI1 (N382S) and WAS (L270P) were observed. The N382S GFI1 mutation was associated with striking monocytosis. A novel nonsense mutation of GFI1 (R412X) was detected in one additional case. As expected, compound heterozygous mutations of SBDS were present in the two cases of SDS. In addition, heterozygous mutations of SBDS (84Cfs3X and Q94X) were observed in two cases of SCN. Typical truncation mutations of CSF3R were detected in 4 cases, all developing MDS or AML. Surprisingly, no mutations of HAX1 were detected. Considering only patients with a diagnosis of SCN who were from North America (125 of the total 159 cases), the incidence of ELA2 mutations was 68%. Eleven novel ELA2 mutations were identified. In 28.8% of cases, no mutation of any gene were detected. Based on these data, we recommend that ELA2 genotyping be performed in all patients with suspected SCN. In the North American population mutations in HAX1, GFI1, SBDS, and WAS are rare and routine genotyping is not indicated. Finally, the data suggest that there are yet undiscovered genetic causes of SCN.