From OMIMTypical hemolytic uremic syndrome is characterized by acute renal failure, thrombocytopenia, and microangiopathic hemolytic anemia associated with distorted erythrocytes ('burr cells'). The vast majority of cases (90%) are sporadic, occur in children under 3 years of age, and are associated with epidemics of diarrhea caused by verotoxin-producing E. coli. The death rate is very low, about 30% of cases have renal sequelae, and there is usually no relapse of the disease. This form of HUS usually presents with a diarrhea prodrome (thus referred to as D+HUS) and has a good prognosis in most cases. In contrast, a subgroup of patients with HUS have an atypical presentation (aHUS or D-HUS) without a prodrome of enterocolitis and diarrhea and have a much poorer prognosis, with a tendency to relapse and frequent development of end-stage renal failure or death. These cases tend to be familial. Both autosomal recessive and autosomal dominant inheritance have been reported (Goodship et al., 1997; Taylor, 2001; Veyradier et al., 2003; Noris et al., 2003). Noris and Remuzzi (2009) provided a detailed review of atypical HUS.
Genetic Heterogeneity of Atypical Hemolytic Uremic Syndrome
Atypical HUS is a genetically heterogeneous condition. Susceptibility to the development of the disorder can be conferred by mutations in various components of or regulatory factors in the complement cascade system (Jozsi et al., 2008). See AHUS2 (612922), AHUS3 (612923), AHUS4 (612924), AHUS5 (612925), and AHUS6 (612926). AHUS7 (see 615008) is caused by mutation in the DGKE gene (601440), which is not part of the complement cascade system. AHUS8 (301110) is caused by mutation in the C1GALT1C1 gene (300611), encoding a molecular chaperone with an essential role in mucin-type O-glycan biosynthesis, on chromosome Xq23.
http://www.omim.org/entry/235400 From MedlinePlus GeneticsAtypical hemolytic-uremic syndrome is a disease that primarily affects kidney function. This condition, which can occur at any age, causes abnormal blood clots (thrombi) to form in small blood vessels in the kidneys. These clots can cause serious medical problems if they restrict or block blood flow. Atypical hemolytic-uremic syndrome is characterized by three major features related to abnormal clotting: hemolytic anemia, thrombocytopenia, and kidney failure.
Hemolytic anemia occurs when red blood cells break down (undergo hemolysis) prematurely. In atypical hemolytic-uremic syndrome, red blood cells can break apart as they squeeze past clots within small blood vessels. Anemia results if these cells are destroyed faster than the body can replace them. Anemia can lead to unusually pale skin (pallor), yellowing of the eyes and skin (jaundice), fatigue, shortness of breath, and a rapid heart rate.
Thrombocytopenia is a reduced level of circulating platelets, which are cells that normally assist with blood clotting. In people with atypical hemolytic-uremic syndrome, fewer platelets are available in the bloodstream because a large number of platelets are used to make abnormal clots. Thrombocytopenia can cause easy bruising and abnormal bleeding.
Atypical hemolytic-uremic syndrome should be distinguished from a more common condition called typical hemolytic-uremic syndrome. The two disorders have different causes and different signs and symptoms. Unlike the atypical form, the typical form is caused by infection with certain strains of Escherichia coli bacteria that produce toxic substances called Shiga-like toxins. The typical form is characterized by severe diarrhea and most often affects children younger than 10. The typical form is less likely than the atypical form to involve recurrent attacks of kidney damage that lead to ESRD.
As a result of clot formation in small blood vessels, people with atypical hemolytic-uremic syndrome experience kidney damage and acute kidney failure that lead to end-stage renal disease (ESRD) in about half of all cases. These life-threatening complications prevent the kidneys from filtering fluids and waste products from the body effectively.
https://medlineplus.gov/genetics/condition/atypical-hemolytic-uremic-syndrome