Cyclic neutropenia (CyN) is a rare hematologic disorder and form of congenital neutropenia that tends to occur approximately every three weeks and lasting for few days at a time due to changing rates of neutrophil production by the bone marrow. It causes a temporary condition with a low absolute neutrophil count and because the neutrophils make up the majority of circulating white blood cells it places the body at severe risk of inflammation and infection. In comparison to severe congenital neutropenia, it responds well to treatment with granulocyte colony-stimulating factor (filgrastim), which increases the neutrophil count, shortens the cycle length, as well decreases the severity and frequency of infections. Signs and symptoms
The common symptoms of neutropenia are recurrent fever, malaise, inflammation of the tissues surrounding the teeth, mouth ulcers, inflammation and bacterial infection of the respiratory tract, digestive tract, skin, and abdominal pain. It is considered that the greatest risk for death is from developing necrotizing enterocolitis (NEC), peritonitis, bacteremia or Clostridium and Escherichia coli sepsis and septic shock, and pneumonia. Causes
Cyclic neutropenia (CyN), like severe congenital neutropenia (SCN), is a rare disorder. It is considered that in the general population, CyN has a frequency of one in one million. It is the result of autosomal dominant mutation in ELANE gene located on the short arm (p) of chromosome 19 (19p13.3), the gene encoding neutrophil elastase, which is also the most common cause of the SCN. It sporadically occurs as a de novo mutation variant or can be present among members of the same family.
In the case of CyN, the mutation variants have been found to mostly cluster in intron 4 and exon 4 and 5, but were also located in intron 3, and exon 2 and 3. Some mutation variants have been found in both Cyn and SCN, which indicates they are phenotypes of the same disease with different severity.It is considered that the mutation causes a decrease in the "neutrophil production or excessive apoptosis (shorter half-life)" which results in a deficiency of mature neutrophils in the blood. The exact pathological mechanism is still researched, with the main hypotheses being mislocalization of ELANE or unfolded protein response (UPR) induced by mutant ELANE, however according to Mehta et al. (2016), the "UPR induction by mutant ELANE is not strong enough to promote cell death and that mutant ELANE causes SCN through an alternative mechanism". According to Garg et al. (2020), new "findings challenge the currently prevailing model that SCN results from mutant ELANE, which triggers endoplasmic reticulum stress, UPR, and apoptosis". The expression of the ELANE gene has been linked to GFI1 gene, and some considered that interaction with other genes causes the emergence and severity of one or the other phenotypic disorder. It is unclear what causes the cyclic aspect in CyN. According to Donadieu et al. (2011), the "cyclic aspect ... suggests the existence of a cryptic biological clock that regulates granulopoiesis. This putative clock might be revealed by particular mutations".