Genetic and Phenotypically Heterogeneity of Patients with Congenital Neutropenia.

Severe congenital neutropenia (CN) is a general term for a group of disorders characterized by extremely low blood neutrophil counts (ANC < 0.5 x 10⁹ ), early stage maturation arrest of myelopoiesis, and recurrent bacterial infections. More than 90% of CN patients respond to daily G-CSF treatment with a sustained neutrophil increase associated with a significant reduction of infections and improved quality of life. However, prolonged survival unmasks an increased risk of leukemic transformation in some, but not all, subcategories of CN patients.

The Severe Chronic Neutropenia International Registry (SCNIR) has collected longitudinal data on on more than 400 patients with various causes of CN. This unique resource allows classification of different subtypes of CN and estimation of the relative frequency of these conditions. Our new classification scheme is as follows:

1. By inheritance - autosomal dominant severe congenital neutropenia (ADCN), autosomal recessive (ARCN, Kostmann syndrome), sporadic CN.

2. By genetic aberrations - ELA2 related CN, SBDS related CN-(Shwachman-Diamond syndrome), G 4.5 on Xq28related neutropenia (Barth syndrome), CXCR4 related neutropenia (myelokathexis and WHIM syndrome).

3. By clinical phenotype - associated symptoms (e. g. metabolic disorders, such as Shwachman-Diamond syndrome, glycogen storage disease 1b, Barth syndrome), G-CSF responsive or non-responsive CN, with or without G-CSF receptor mutations, with or without osteoporosis, or dysplastic features (e. g. organ abnormalities).

4. By ethnic origin - e.g. CN in consanguineous Kurdish families, recessive neutropenia in Swedish family (Kostmann syndrome).

Recent research and the work of the SCNIR now permit a much improved classification of CN. The identification of subtypes of CN, their distinctive risks of malignant transformation, and their responses to treatment has contributed substantially to our general understanding of the problem of neutropenia. This knowledge also now allows clinicians to give patients and families much improved prognostic information and better guidelines for therapy.