Porphyria Educational Services
PORPHYRIA EDUCATIONALSERVICES BULLETIN
Vol. 1 No. 45 October 31, 1999
FOCUS: A Variant Form of Acute Intermittent Porphyria
For a diagnosis of most acute intermittent porphyria, a confirmed diagnosis comes by the positive 24 hour quanitative urine testing and a red blood cell tests showibng a marked decreased in the PBG-deaminase.
However in 1981 Dr. P. Mustajoki suggested that in one variant of acute intermittent porphyria the enzyme defect is not expressed in red cells. Dr. Mustajoki studied a large family in which 10 members had AIP with the normal erythrocyte PBG-deaminase activity. Forty-nine other patients with AIP who were unrelated to this kindred had the usual low activity of PBG-deaminase.
Generally, however, reduced activity of this enzyme in red cells is a consistent finding during or between acute attacks, and characterizes latent AIP that is inherited as an autosomal dominant trait. More on this can be found in writings by Dr. Shigeri Sassa and others in 1974 as well as Dr. Kreimer-Birnbaum, in 1975.
While the initial study was undertaken in northern Europe, the finding of this variant form of acute intermittent porphyria is not limited to the northern reaches of Europe has has been documented within the United States and in families living on the west coast of England.
Most enzymopathies are recessively inherited because few enzymes are so rate-limiting as to cause a serious reduction in the rate of a metabolic pathway when the enzyme has 40 to 60% normal activity.
So how does this this variant form of AIP show up in genetic coding?
Genetic mapping for my family looks like this:ALA enzyme AIP syndrome Inheritance pattern AB Location 9q glutamine for arginate mutation at 168 or position 173 arg 167 -to-gin Chromosome 11q 24.1-1q 24.2 Dominant Exon 10.
There are new variants being found all the time in the difference forms of porphyria. As one researcher stated it: "We are only now at the tip of the iceberg. We have many miles to go and lots of discovers to make where'porphyria is concerned."