Novel HAX1 mutations in patients with severe congenital neutropenia reveal isoform-dependent genotype-phenotype associations.

Homozygous mutations in HAX1 cause an autosomal recessive form of severe congenital neutropenia (CN). By screening 88 patients with CN, we identified 6 additional patients with HAX1 mutations carrying 4 novel mutations. Of these, 2 affect both published transcript variants of HAX1; the other 2 mutations affect only transcript variant 1. Analysis of the patients' genotypes and phenotypes revealed a striking correlation: Mutations affecting transcript variant 1 only were associated with CN (23 of 23 patients), whereas mutations affecting both transcript variants caused CN and neurologic symptoms, including epilepsy and neurodevelopmental delay (6 of 6 patients). In contrast to peripheral blood, transcript variant 2 was markedly expressed in human brain tissue. The clinical phenotype of HAX1 deficiency appears to depend on the localization of the mutation and their influence on the transcript variants. Therefore, our findings suggest that HAX1 isoforms may play a distinctive role in the neuronal system.

The clinical, immunohematological, and molecular study of Iranian patients with severe congenital neutropenia.

Severe congenital neutropenia (SCN) is a rareE primary immunodeficiency disorder characterized by early onset recurrent infections in association with persistent severe agranulocytosis. To identify the clinical, immunohematological, and molecular characteristics of patients with SCN, 18 Iranian patients with the mean age of 8.8 +/- 5.8 years were investigated in this study. All of these patients experienced severe neutropenia; the mean of absolute neutrophil count was 281.4 +/- 137.7 cells/mm3. Bone marrow findings were typified by a myeloid maturation arrest at the promyelocyte-myelocyte stage in these patients. Molecular analysis revealed different mutations in the ELA-2 gene of one patient and in the HAX-1 gene of another three patients. The most common presenting complaints in these patients were superficial abscesses, oral ulcers, cutaneous infections, omphalitis, and pneumonia. During the course of illness, all patients developed mucocutaneous manifestations, and 16 cases had respiratory infections. The most commonly manifestations were abscesses, oral ulcers, pneumonia, periodontitis, otitis media, cutaneous infections, mucocutaneous candidiasis, and acute diarrhea. Three patients died because of a severe infection. Although SCN is a rare disorder, early onset of severe and recurrent infections should always raise a suspicion, which deserves further evaluation for detecting such disorder.

HAX1 deficiency causes autosomal recessive severe congenital neutropenia (Kostmann disease).

Autosomal recessive severe congenital neutropenia (SCN) constitutes a primary immunodeficiency syndrome associated with increased apoptosis in myeloid cells, yet the underlying genetic defect remains unknown. Using a positional cloning approach and candidate gene evaluation, we identified a recurrent homozygous germline mutation in HAX1 in three pedigrees. After further molecular screening of individuals with SCN, we identified 19 additional affected individuals with homozygous HAX1 mutations, including three belonging to the original pedigree described by Kostmann. HAX1 encodes the mitochondrial protein HAX1, which has been assigned functions in signal transduction and cytoskeletal control. Here, we show that HAX1 is critical for maintaining the inner mitochondrial membrane potential and protecting against apoptosis in myeloid cells. Our findings suggest that HAX1 is a major regulator of myeloid homeostasis and underline the significance of genetic control of apoptosis in neutrophil development.