Mastocytosis

Description

• Two clinical diagnostic categories: cutaneous mastocytosis (CM) or systemic mastocytosis (SM)
• CM only is the most common form, whereas SM constitutes only 10–15% of all the cases.
• CM consistency primarily of skin involvement with characteristic lesions, urticaria pigmentosa (UP)
• Symptoms of mastocytosis are from mast cell degranulation and release of chemical mediators, such as histamine, leukotrienes, and prostaglandins.
• In adults, mastocytosis often is secondary to a gain-of-function point mutation in the proto-oncogene c-kit (D⁸¹⁶V in >95% of cases) leading to clonal proliferation of mast cells.
• Childhood mastocytosis is associated with c-kit, D⁸¹⁶V in only 40% of cases; majority of cases are limited to the skin and have excellent prognosis with spontaneous resolution around puberty.

Epidemiology

• Incidence and prevalence will vary because many cases remain undiagnosed.
• Prevalence estimated 1 in 60,000 people.
• Incidence 0.1 to 1/100,000 people per year in United States
• ~2/3 of reported CM cases are found in children, most diagnosed before the age of 2 years.
• Adults more likely to have systemic disease and onset between 20 and 50 years with diagnosis at 40 to 60 years
• Prevalence equal in males and females

Etiology and Pathophysiology

Genetics
The disease is congenital in 15–25% of cases.

• Gain-of-function point mutations in c-kit, in particular D⁸¹⁶V
  • C-kit (KIT) is a proto-oncogene that encodes for a tyrosine kinase receptor (CD117 transmembrane receptor) located on many hematopoietic stem cells, including mast cells.
  • Normally, stem cell factor (SCF) binds to CD117 leading to mast cell growth, migration, survival.
  • Autophosphorylation of tyrosine residues in the presence of gain-of-function c-kit mutations leads to unregulated proliferation of mast cells.
  • Mutations in other genes may also be pathogenic in some cases.
  • There is no known genetic transmission.

Risk Factors

Age; c-kit–activating mutations