Neutropenia is defined as an absolute neutrophil count (ANC) of less than 1500/microliter in adults and 1000/microliter in infants under the age of 1-year. In benign neutropenia, as the name suggests, the condition is mild with ANCs ranging between 800 and 1400/microliter. This mild decrease in neutrophils is only seen in the circulating pool, with the bone marrow pools, marginal blood pools, and tissue pools of neutrophils displaying normal levels. Unlike other chronic neutropenias, benign familial neutropenia is not associated with an increased risk of infection, apart from cases of periodonitis. Affected individuals, for the most part, remain symptomless, and no treatment is required. The condition has been reported in certain families of European, African, and Yemeni Jewish origin.
Both hereditary and acquired forms of chronic benign neutropenia have been observed. The familial forms have been noted to follow an autosomal dominant mode of inheritance. However, the mechanism of pathogenesis is not known.
Denic et al. (2009) studied the prevalence of benign neutropenia in an unbiased sample of 1,032 healthy Emirati subjects. The overall prevalence of neutropenia was found to be 10.7%. The mean neutrophil count in the entire sample (3300/microliter) was found to be lower than that reported among American Mexicans, Whites and older Blacks. No significant difference in the differential leukocyte counts or prevalence of neutropenia was seen between the sexes and different age groups. Marked neutropenia was seen in 24 subjects (2.3%). However, these subjects had normal hemoglobin and platelet counts. Denic et al. (2009) stressed that this observed prevalence of benign neutropenia could be an underestimate, since subjects could periodically have ANCs in the normal range. Interestingly, the neutrophil count was found to directly correlate with monocyte counts in the subjects, prompting the idea of a single progenitor cell being involved in the mechanism of the condition. Denic et al. (2009) also studied a cohort of seven subjects with benign neutropenia. Unlike any in the first cohort, six subjects in the second cohort displayed agranulocytic neutropenia at least once. These patients were classified based on their ANCs as having mild neutropenia (2), more profound neutropenia (2), and cycling neutropenia (2). Pedigrees of four of these families were also studied, which pointed to an autosomal dominant form of inheritance. In one of these families, mild congenital neutropenia was excluded on the basis of absence of mutations in the ELA2 and HAX1 genes. Denic et al. (2009) concluded that this high prevalence of benign neutropenia could be a consequence of adaption to endemic malaria, and that population screening needs to be undertaken to assess the true definition of neutropenia in Arab populations.
Djaldetti et al. (1961) were the first to record observations on familial neutropenia in 11 Jewish families from Yemen.
Dale et al. (1979) stated that lower neutrophil counts in African and American blacks and in Yemenite Jews are of little or no clinical consequence.
Weingarten et al. (1993) reviewed the blood counts of 372 Yemenite Jews. About 21% were found to have leukocyte counts below 55/microliter, while 15.4%, with counts less than 200/microliter, were classified as neutropenic. Average lymphocyte and erythrocyte counts were normal. Weingarten et al. (1993) concluded that benign leucopenia, thought to be common in this population, ought to be defined as neutropenia.