Association Between Absolute Neutrophil Count and Variation at TCIRG1: The NHLBI Exome Sequencing Project.
Autosomal recessive severe congenital neutropenia (SCN) results from a maturation arrest of granulopoiesis at the level of promyelocytes and apoptosis of myeloid cells. In SCN patients, mutations have been described in the HAX1 gene. Most of the SCN patients who carry nonsense mutations that are common to both transcript variants of the HAX1 gene also exhibit neurological deficits. This study describes an SCN patient with neurological manifestations including daily episodes of atonic seizures, learning disabilities, and developmental delay. Sequencing of the HAX1 gene of this SCN patient identified a novel nonsense c.463_464insC homozygous mutation in exon 3, which is common to both transcript variants of the gene. This mutation encodes for a p.Gln155ProfsX14 change and causes premature truncation of the HAX1 protein. Neutrophils isolated from the patient exhibited spontaneous apoptosis and loss of inner mitochondrial membrane potential, which were further enhanced upon treatment with hydrogen peroxide. This study adds to the spectrum of novel HAX1 gene mutations and disease manifestations in ethnically distinct SCN patients. Our report describes the only nonsense mutation in the HAX1 gene present in SCN patients of Arab origin.