Influence of age and gender on the clinical expression of acute intermittent porphyria based on molecular study of porphobilinogen deaminase gene among Swiss patients.

BACKGROUND: Acute intermittent porphyria (AIP) is an inherited disorder in the heme biosynthetic pathway caused by a partial deficiency of porphobilinogen (PBG) deaminase. Clinically, AIP is characterized as acute neurovisceral attacks that are often precipitated by exogenous factors such as drugs, hormones, and alcohol. An early detection of mutation carriers is essential for prevention of acute attacks by avoiding precipitating factors. This study was aimed at analyzing genetic defects causing AIP among Swiss families to further investigate aspects concerning the clinical expression of the disease. MATERIALS AND METHODS: The PBGD gene of index patients from 21 Swiss AIP families was systematically analyzed by denaturing gradient gel electrophoresis of polymerase chain reaction (PCR) amplified DNA fragments and direct sequencing. RESULTS: Five new mutations insA503, del L170, T190I, P241S, and R321H, as well as three known mutations (R26H, R173Q and W283X) were detected. Twelve of the 21 index patients (57%) carried the prevalent mutation W283X previously found among the Swiss AIP population. Family-specific mutations were then screened among relatives of the index patients. Among the 107 studied individuals, 58 carried a PBGD gene mutation--30 were overt AIP patients and 28 were asymptomatic carriers. The apparent rate of overt disease in the study cohort was 52%, which is significantly higher than the previously reported penetrance of 10-20%. To further examine the clinical expression of AIP, the cumulative life-time risk was calculated among 58 mutation-positive individuals after stratifying for age. The result shows a linear increase of the percentage of the symptomatic patients with age, reaching up to 75% among carriers aged over 60. Moreover, statistical analysis of the gender distribution among patients and asymptomatic carriers indicated that the disease was more frequently expressed among females than males (Fisher's exact test two sided, p= (0.001). CONCLUSIONS: This comprehensive search for genetic defects in the PBGD gene confirmed the existence of a prevalent mutation W283X among Swiss AIP patients, as well as a number of family-private mutations. Genetic analysis laid a groundwork for further studies such as the effects of gender and age on the clinical expression of AIP.

Haplotype analysis in determination of the heredity of erythropoietic protoporphyria among Swiss families.

Defects in the human ferrochelatase gene lead to the hereditary disorder of erythropoietic protoporphyria. The clinical expression of this autosomal dominant disorder requires an allelic combination of a disabled mutant allele and a low-expressed nonmutant allele. Unlike most other erythropoietic protoporphyria populations, mutations identified among Swiss erythropoietic protoporphyria families to date have been relatively homogeneous. In this study, genotype analysis was conducted in seven Swiss erythropoietic protoporphyria families, three carrying mutation Q59X, two carrying mutation insT213, and two carrying mutation delTACAG(580-584). Three different haplotypes of five known intragenic single nucleotide polymorphisms, namely -251 A/G, IVS1-23C/T, 798 G/C, 921 A/G, and 1520C/T, were identified. Each haplotype was shared by families carrying an identical mutation in the ferrochelatase gene indicating a single mutation event for each of the three mutations. These mutations have been present in the Swiss erythropoietic protoporphyria population for a relatively long time as no common haplotypes of microsatellite markers flanking the ferrochelatase gene were found, except of two conserved regions, telomeric of the insT213 allele and centromeric of the delTACAG(580-584)allele, each with a size > 3 cM. Among the nonmutant ferrochelatase alleles, patients from six erythropoietic protoporphyria families shared a common haplotype [-251G; IVS1-23T] of the first two single nucleotide polymorphisms. An exception was the haplotype [-251 A; IVS1-23C] identified in the index patient of one erythropoietic protoporphyria family. These results supported the recent findings that the low expressed allele is tightly linked to a haplotype [-251G; IVS1-23T] of two intragenic single nucleotide polymorphisms in the ferrochelatase gene.

Identification of a prevalent nonsense mutation (W283X) and two novel mutations in the porphobilinogen deaminase gene of Swiss patients with acute intermittent porphyria.

Acute intermittent porphyria (AIP) is an autosomal dominant disorder caused by decreased activity of porphobilinogen deaminase (PBGD), the third enzyme in the heme biosynthetic pathway. We report the first molecular analysis of PBGD gene mutations in AIP patients of Swiss origin. The PBGD gene of 18 Swiss AIP patients was analyzed by denaturing gradient gel electrophoresis screening of the genomic DNA and direct sequencing. Thirteen of the 18 patients (72%) carried a nonsense mutation G(849)-->A, W283X. In addition, 4 different mutations including 2 novel mutations (Q217L and Q292X), were identified in the 5 remaining AIP patients originating from both German- and Italian-speaking regions of Switzerland.

Rapid molecular diagnosis of erythropoietic protoporphyria among Swiss patients.

Erythropoietic protoporphyria (EPP) is an autosomal dominant inherited disorder with incomplete penetrance. It is caused by partial deficiency of ferrochelatase, the last enzyme in the heme biosynthetic pathway. Measurement of protoporphyrin concentrations in red cells and feces, although sufficient for diagnosis of symptomatic EPP patients, fails to detect asymptomatic gene carriers. We have developed a molecular diagnostic procedure for rapid and reliable screening of five known mutations in the ferrochelatase gene among Swiss EPP patients in a single denaturing gradient gel electrophoresis (DGGE) gel.

Systematic analysis of molecular defects in the ferrochelatase gene from patients with erythropoietic protoporphyria.

Erythropoietic protoporphyria (EPP; MIM 177000) is an inherited disorder caused by partial deficiency of ferrochelatase (FECH), the last enzyme in the heme biosynthetic pathway. In EPP patients, the FECH deficiency causes accumulation of free protoporphyrin in the erythron, associated with a painful skin photosensitivity. In rare cases, the massive accumulation of protoporphyrin in hepatocytes may lead to a rapidly progressive liver failure. The mode of inheritance in EPP is complex and can be either autosomal dominant with low clinical penetrance, as it is in most cases, or autosomal recessive. To acquire an in-depth knowledge of the genetic basis of EPP, we conducted a systematic mutation analysis of the FECH gene, following a procedure that combines the exon-by-exon denaturing-gradient-gel-electrophoresis screening of the FECH genomic DNA and direct sequencing. Twenty different mutations, 15 of which are newly described here, have been characterized in 26 of 29 EPP patients of Swiss and French origin. All the EPP patients, including those with liver complications, were heterozygous for the mutations identified in the FECH gene. The deleterious effect of all missense mutations has been assessed by bacterial expression of the respective FECH cDNAs generated by site-directed mutagenesis. Mutations leading to a null allele were a common feature among three EPP pedigrees with liver complications. Our systematic molecular study has resulted in a significant enlargement of the mutation repertoire in the FECH gene and has shed new light on the hereditary behavior of EPP.