A splicing mutation in the hydroxymethylbilane synthase gene in a Japanese family with acute intermittent porphyria

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

BACKGROUND

Acute intermittent porphyria (AIP) is caused by a partial deficiency of hydroxymethylbilane synthase and affects heme biosynthesis. Mutations in the HMBS gene result in HMBS deficiency. AIP is a rare disease, and there been insufficient studies on it. This report describes the molecular epidemiology of HMBS gene defects and hydroxymethylbilane synthase activity levels in classical AIP.

METHODS

Databases of PubMed, CNKI, and Wang Fang Database were searched for eligible studies to investigate HMBS gene mutations in peripheral blood samples and HMBS activity in erythrocytes of patients with classical AIP. Relevant studies published up to July 15, 2023, from several databases were independently searched and selected by 2 reviewers. Accuracy data and relevant information were extracted from each eligible study by 2 independent researchers and analyzed using statistical software.

RESULTS

After pooling the accuracy data from 232 patients of the 15 eligible studies, 90.5% (210/232) of AIP patients had decreased erythrocyte hydroxymethylbilane synthase activity (<70%), and 96 different mutations were identified in 232 patients, including 33 missense (34.4%), 27 splice (28.1%), 19 deletion (19.8%), 8 nonsense (8.3%), 9 insertion (9.4%) mutations. Residual enzyme activities (%) for different groups of type were expressed using mean and 95% confidence interval (95% CI): missense (51.2, 48.5-53.9), splice (57.5, 52.0-59.1), deletion (54.9, 50.7-59.1), nonsense (52.2, 44.4-60.0), insertion (53.2, 47.4-59.0), group analysis P = .17. Subgroups of missense mutations, domain 1 (50.2, 46.0-54.4), domain 2 (52.8, 49.1-56.4), and domain 3 (49.2, 38.3-60.0), Subgroup analysis, P = .62.

CONCLUSION

Different mutation types and mutation positions are not associated with the level of hydroxymethylbilane synthase activity. Erythrocyte hydroxymethylbilane synthase activity is often reduced to half of normal in patients with AIP, and the enzyme activity assay has a high diagnostic value in AIP. AIP is highly molecularly heterogeneous, with missense mutations being the most common, followed by splice mutations. R173W and G111R are high-frequency mutations and have been found in multiple families from different countries.

Novel hydroxymethylbilane synthase gene mutation identified and confirmed in a woman with acute intermittent porphyria: A case report

BACKGROUND

Acute intermittent porphyria (AIP) is a rare autosomal dominant porphyrin metabolic disease caused by a mutation in the hydroxymethylbilane synthase(HMBS) gene. This study aimed to explore the clinical manifestations of a patient with AIP, to identify a novel HMBS gene mutation in the proband and some of her family members, and to confirm the pathogenicity of the variant.

CASE SUMMARY

A 22-year-old Chinese woman developed severe abdominal pain, lumbago, sinus tachycardia, epileptic seizure, hypertension, and weakness in lower limbs in March, 2018. Biochemical examinations indicated hypohepatia and hyponatremia. Her last menstrual period was 45 d prior to admission, and she was unaware of the pregnancy, which was confirmed by a pregnancy test after admission. Sunlight exposure of her urine sample for 1 h turned it from yellow to wine red. Urinary porphyrin test result was positive. Based on these clinical manifestations, AIP was diagnosed. After increasing her daily glucose intake (250–300 g/d), abdominal pain was partially relieved. Three days after hospitalization, spontaneous vaginal bleeding occurred, which was confirmed as spontaneous abortion; thereafter, her clinical symptoms completely resolved. Genetic testing revealed a novel heterozygous splicing variant of the HMBS gene in exon 10 (c.648_651+1delCCAGG) in the proband and four other family members. The pathogenicity of the variant was verified through bioinformatic methods and a minigene assay.

CONCLUSION

We identified a novel HMBS gene mutation in a Chinese patient with AIP and confirmed its pathogenicity.

False-positive accumulation of metaiodobenzylguanidine in a case with acute intermittent porphyria

We report a 36-year-old woman presenting with hypertensive encephalopathy followed by bulbar palsy and quadriplegia. After an extensive screening for secondary causes of hypertension, the patient was suspected of having pheochromocytoma due to increased levels of catecholamines in the plasma and the urine, and positive (131)I-metaiodobenzylguanidine (MIBG) accumulation in the gallbladder. However, MIBG accumulation was not reproducible without any tumors accompanying this accumulation in the gallbladder. A diagnosis of acute intermittent porphyria was finally confirmed based on the characteristic pictures, increased urinary excretion of porphobilinogen, and identification of a heterozygous missense mutation of R173W in the hydroxymethylbilane synthase gene. This case highlights a pitfall in utilizing MIBG to detect a source of excessive catecholamine and also suggests the importance of having a complete clinical history and extensive work-up of any possible differential diagnosis. We also review the potential mechanism by which false-positive MIBG accumulation occurs.