Acatalasia, a deficiency of the enzyme catalase, is a relatively benign condition in which the substrate, hydrogen peroxide, may accumulate. Many patients with acatalasia are asymptomatic, while some develop mouth sores.
Acatalasia (acatalasemia, catalase deficiency) is a rare genetic condition displaying a pattern of autosomal recessive inheritance. The catalase enzyme catalyzes the breakdown of hydrogen peroxide, a dangerous compound with oxidizing potential, into water and oxygen. Low levels of enzyme activity may lead to tissue damage under some conditions such as an infection by certain bacteria because a defense against the oxidative effects of hydrogen peroxide is compromised. However, other enzymes also function in the decomposition of hydrogen peroxide, which helps to ameliorate the effect of low catalase levels. Another reason for the condition being benign is that absence of catalase is rarely complete, and some residual activity can usually be found.
A variety of mutations may be responsible for the enzyme deficiency. As a result, the nature of the defect in the protein and the clinical manifestations vary. Until now, three main types of acatalasia have been distinguished (there are relevant subtypes, too). The first is the Japanese type, which is also the type that was first described. The condition of acatalasia was originally identified when a patient with mouth sores underwent surgery and on rinsing the wounds with hydrogen peroxide no bubbles were observed, indicating the absence of catalase activity . The Japanese type of acatalasia, also called Takahara disease, is often characterized by mouth sores and gangrenes, although the incidence of oral problems is decreasing as oral care keeps improving. The second type was identified in Switzerland . People having this condition are often free of symptoms. The third type of acatalasia, described in Hungary, is variable and is frequently associated with type II diabetes .
In addition to diabetes mellitus, atherosclerosis, Wilms tumor, and aniridia can be associated with acatalasia . In patients with acatalasia, the high levels of hydrogen peroxide may lead to methemoglobinemia. This may be a particular concern for acatalasemic patients undergoing uric acid oxidase treatment during chemotherapy because this can result in very high concentrations of hydrogen peroxide .
Patient history and physical examination are indispensable for discovering the signs (mainly mouth sores or gangrenes) suggestive of acatalasia. Verification of the disease can be made by the simple test of exposing blood to hydrogen peroxide to observe the features of acatalasia, which are the absence of bubbles and the blood turning very quickly brown. Since many people with acatalasia are asymptomatic, they are often diagnosed through screening.
Full diagnosis requires the physicochemical characterization of the protein and the molecular genetic identification of the defect.
The enzyme activity can be measured in red blood cells. The molecular weight, isoelectric point, thermal stability, and catalytic constants of the catalase from patients with the Japanese acatalasia I condition are the same as those of the normal enzyme; however, the quantity of the protein is severely diminished . In contrast, the Swiss-type enzyme – and some of the Hungarian types - have altered features, among them a decreased stability, showing that the protein is defective.
Molecular characterization of sequence alterations causing acatalasia shows heterogeneity among the patients. In the Japanese acatalasia I condition, sequencing of the gene and other studies demonstrated a splicing mutation . Point mutations causing decreased activity of the enzyme have been observed in some Hungarian type conditions , whereas frameshift mutations were found in Hungarian and some Japanese patients  .