Atypical HUS or Atypical Hemolytic Uremic Syndrome (aHUS) is a condition that is characterized by the following three signs:
  • Hemolysis or fragmentation of the red blood cells
  • Thrombocytopenia or a low platelet count
  • Declining kidney function
Sometimes, though not very commonly, aHUS also affects other organs and systems within the body such as the Neurological system. aHUS must be distinguished from Typical HUS or just HUS. While HUS is typically caused by an external agent such as bacteria, aHUS is mostly caused by an internal sequence of events. While HUS is associated with quick, complete recovery, aHUS is often more difficult to completely recover from. HUS is often preceded by severe diarrhea which could also be bloody. Symptoms Symptoms could be fairly mild and often develop gradually:
  • General feeling of being unwell
  • Dark urine
  • Nausea, vomiting
  • Fatigue, tiredness
  • Irritability
On visiting a doctor, some tests are typically prescribed and in a Complete Blood Picture (CBP, Hemogram, CBC etc.), the following findings would generally be associated with aHUS:
  • Low Hemoglobin
  • Low Platelet Counts
  • Fragmented blood cells or schistocytes on the smear
Further a test for Serum Creatinine or Blood Urea (or BUN - Blood Urea Nitrogen) may also show elevated values. Causes aHUS can be familial or sporadic. Familial aHUS is when other members of the family have also had the disease. This has been very rare. The sporadic form is when the patient is the first member of the family to have been detected with aHUS. There have been two known causes identified so far of aHUS:
  • Genetic mutations
  • External causes such as pregnancy or HIV
Quite a few specific genetic mutations have been implicated in aHUS. Some of them are:
  • Complement Factor H
  • Complement Factor H R1/3
  • Membrane Cofactor Protein
  • Complement Factor I
  • Complement Factor B
  • Complement C3
  • Thrombomodulin
Each of these have a different outcome. Hence it is important to determine which specific mutation is involved. Many cases of aHUS have not been associated with any cause yet but are believed to be due to a genetic mutation which has not yet been discovered. These are classified as Idiopathic - of unknown cause.