De novo mutation found in the porphobilinogen deaminase gene in Slovak acute intermittent porphyria patient: Molecular biochemical study

Abstract

The porphyrias are group of mostly inherited disorders in which a specific spectrum of accumulated and excreted porphyrins and heme precursors are associated with characteristic clinical features. There are eight enzymes involved in the heme synthesis and defects in seven of them cause porphyria. Four of them are described as acute hepatic porphyrias, which share possible precipitation of acute attacks with symptoms engaging the nervous system. Acute intermittent porphyria (AIP), caused by partial deficiency of the porphobilinogen deaminase (PBGD), is the most frequent among hepatic porphyrias. Clinical expression is highly variable and ~ 90 % of AIP heterozygotes remain asymptomatic throughout life. During systematic genetic analysis of the AIP patients diagnosed in the Czech and Slovak Republics, we found a special case of AIP. In a 15-year-old boy with abdominal and subsequent neurological symptomatology, we identified de novo mutation 966insA within the PBGD gene leading to a stop codon after 36 completely different amino acids compared to the wt-sequence. To establish the effects of this mutation on the protein structure, we expressed mutant constructs with described mutation in E. coli and analyzed their biochemical and enzymatic properties. Moreover, computer-assisted protein structure prediction was performed.

HMBS gene mutations and hydroxymethylbilane synthase activity in acute intermittent porphyria: A systematic review

“…Currently, some mutations have been tested for enzyme activity analysis in vitro, The enzyme activity of homozygotes of most mutations in vitro expressed <5%, which is consistent with the decrease of half the residual enzyme activity of heterozygotes in vivo. [9,10,20,21,23,24,32–38] However, some of the homozygotes in vitro expressed the enzyme activity close to normal, ex. c.532 G>A and c.176 C>T, the residual enzyme activity of the homozygote reached 81% in vitro, while the heterozygote residual enzyme activity was 40% in vivo, [10,34] the reasons for this phenomenon need to be further explored.…”