Atypical hemolytic-uremic syndrome (aHUS) is a disease that causes abnormal blood clots to form in small blood vessels in the kidneys. These clots can cause serious medical problems if they restrict or block blood flow, including hemolytic anemia, thrombocytopenia, and kidney failure. It can occur at any age and is often caused by a combination of environmental and genetic factors. Genetic factors involve genes that code for proteins that help control the complement system (part of your body’s immune system). Environmental factors include certain medications (such as anticancer drugs), chronic diseases (e.g., systemic sclerosis and malignant hypertension), viral or bacterial infections, cancers, organ transplantation, and pregnancy.  Most cases are sporadic. Less than 20 percent of all cases have been reported to run in families. When the disorder is familial, it can have an autosomal dominant or an autosomal recessive pattern of inheritance.^[1][2]

Atypical hemolytic-uremic syndrome differs from a more common condition called typical hemolytic-uremic syndrome. The two disorders have different causes and different signs and symptoms.^[2]

• The Merck Manual provides information on the complement system. The Merck Manuals are a series of healthcare books for medical professionals and consumers.
• The Foundation for Children with Atypical HUS provides further information on atypical HUS on their Web site. Click on the link above to view the information page.
  
• Genetics Home Reference (GHR) contains information on Atypical hemolytic uremic syndrome. Click on the link to go to GHR and review the information.
• The National Organization for Rare Disorders (NORD) is a federation of more than 130 nonprofit voluntary health organizations serving people with rare disorders. Click on the link to view information on this topic.
• Orphanet is a European reference portal for information on rare diseases and orphan drugs.  Access to this database is free of charge.  Click on the link to read information on this topic.
• PubMed is a searchable database of medical literature and lists journal articles that discuss Atypical hemolytic uremic syndrome. Click on the link to view a sample search on this topic.
• The The Online Mendelian Inheritance in Man (OMIM) database contains genetics resources that discuss Atypical hemolytic uremic syndrome. Click on the link to go to OMIM and review these resources.