Argininemia as a cause of severe chronic stunting in a low-resource developing country setting: a case report

Detection of interferon alpha and beta receptor subunit 1 (IFNAR1) loss-of-function Glu386∗ variant by tri-allelic genotyping

Mutations of the human interferon alpha and beta receptor subunit 1 (IFNAR1) gene are associated with severe viral infections. Individuals homozygous for the Glu386∗ variant have impaired type I interferon signalling and can suffer severe illness when exposed to certain viruses and live attenuated virus vaccines. Glu386∗ heterozygotes are clinically unaffected, but can pass the variant allele to their descendants. We aimed to develop an assay that can identify IFNAR1 Glu386∗ homozygotes and heterozygotes to support urgent clinical diagnosis, and that can use dried blood spots (DBS) sent at ambient temperature to overcome geographical logistical challenges in the South Pacific region. The tri-allelic genotyping assay interrogates a single nucleotide polymorphism (rs201609461) located in IFNAR1. The reference allele G encodes for wild-type IFNAR1. Minor alleles A (c.1156G>A) and T (c.1156G>T) encode for Glu386Lys and a truncated IFNAR1 protein (p.Glu386∗), respectively. Synthetic oligonucleotides were mixed in equal molar ratio to create six different genotypes which were randomly assigned to 960 genotyping reactions by R software. Three different fluorescence probes were designed to discriminate the three alleles (G, T and A) within a pair of flanking primers in a single genotyping reaction. The assay discriminated all three alleles using DBS from Guthrie cards randomly spiked with synthetic oligonucleotides. We correctly identified all the different genotypes in 960 reactions in these blinded experiments. These findings validate the genotyping assay for rapidly identifying the IFNAR1 Glu386∗ variant from DBS.

Recurrent hepatic failure and status epilepticus: an uncommon presentation of hyperargininemia

Argininemia is a rare hereditary disease due to a deficiency of hepatic arginase, which is the last enzyme of the urea cycle and hydrolyzes arginine to ornithine and urea. Herein we report a patient with arginase I (ARG1) deficiency who presented with recurrent nonconvulsive status epilepticus and liver failure. A novel homozygous frameshift mutation c.703_707delGGACTinsAGACTGGACC (p.G235Rfs*20) was detected.