Rare DIsease Day #2022RAREDISEASE

  • Feb 27, 2022

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If it is not porphyria what else could it be?


Did you know? The prevalence of porphyria remains unknown, but clinicians suggest that a range of 1 per 500-50,000 of population is probable. Some forms of porphyria are more common in specific populations including, for example, in Finland.

Affected Populations

In Europe the prevalence of symptomatic AIP is reported to be 5.9 per million people in the general population., It is likely to be similar elsewhere in the world apart from Sweden where it is higher due to a founder effect. Recent population based genetic studies have shown that approximately 1 in 2000 of the population inherit a disease causing (pathogenic) mutation in the HMBS gene. This suggests that only 1% of those who inherit a pathogenic mutation will ever experience porphyria symptoms. AIP can occur in individuals of all ethnic backgrounds, although it may be less frequently reported in African-American individuals. Women are affected by symptomatic AIP more often than men. The disorder is most common in young or middle-aged women.

Related Disorders

Symptoms of the following disorders can be similar to those of AIP. Comparisons may be useful for a differential diagnosis.

The acute attacks that characterize AIP are similar to those seen in three other forms of porphyria specifically variegate porphyria, hereditary coproporphyria, and ALA-Dehydratase deficiency porphyria. Collectively, these four forms of the porphyria are classified as the acute porphyrias. (For more information on these disorders, choose the specific disorder as your search term in the Rare Disease Database.)

Guillain-Barré syndrome (GBS) is a rare, rapidly progressive disorder that consists of inflammation of the nerves (polyneuritis) causing muscle weakness, sometimes progressing to complete paralysis. Although the precise cause of GBS is unknown, a viral or respiratory infection precedes the onset of the syndrome in about half of the patients. This has led to the theory that GBS may be an autoimmune disease (caused by the body’s own immune system). Damage to the covering (myelin) of nerve axons (the extension of the nerve cell that conducts impulses away from the nerve cell body) results in delayed nerve signal transmission. This causes weakness of the muscles that are supplied by the damaged nerves. The following variants of GBS (acute inflammatory neuropathy or acute inflammatory demyelinating polyradiculoneuropathy) are recognized: Miller Fisher syndrome, acute motor-sensory axonal neuropathy, acute motor axonal neuropathy. (For more information on this disorder, choose “Guillain Barre” as your search term in the Rare Disease Database.)

Tyrosinemia type I is a rare autosomal recessive genetic metabolic disorder characterized by lack of the enzyme fumarylacetoacetate hydrolase (FAH), which is needed for the final break down of the amino acid tyrosine. Failure to properly break down tyrosine leads to abnormal accumulation of tyrosine and its metabolites in the liver, including a heme precursor ALA, potentially resulting in severe liver disease. Tyrosine may also accumulate in the kidneys and central nervous system. Symptoms and physical findings associated with tyrosinemia type I appear in the first months of life and include failure to gain weight and grow at the expected rate (failure to thrive), fever, diarrhea, vomiting, an abnormally enlarged liver (hepatomegaly), and yellowing of the skin and the whites of the eyes (jaundice). Tyrosinemia type I may progress to more serious complications such as severe liver disease, cirrhosis, and hepatocellular carcinoma if left untreated. Untreated children can also suffer neurological crises similar to those seen in acute porphyria. Treatment with nitisinone and a low-tyrosine diet should begin as soon as possible after the diagnosis is confirmed. (For more information on this disorder, choose “tyrosinemia” as your search term in the Rare Disease Database.)

Lead toxicity can cause symptoms that mimic acute porphyria (acute abdominal pain, constipation, neuropathy). Lead inhibits several of the enzymes of haem biosynthesis, which can therefore result in an increase in urine coproporphyrin and 5-aminolevulinic acid excretion, but not porphobilinogen excretion. It can also cause an increase in erythrocyte protoporphyrin concentration, although this is all the zinc-chelate form (zinc-protoporphyrin). The definitive test for lead poisoning is blood lead measurement.