Novel mutation (R192C) in CYB5R3 gene causing NADH-cytochrome b5 reductase deficiency in eight Indian patients associated with autosomal recessive congenital methemoglobinemia type-I

Abstract

Eight index cases from four unrelated families were referred for the cause of cyanosis. All patients showed mild to moderate cyanosis without mental retardation or any neurologic abnormalities. The methemoglobin levels were in the range of 11.5-22.41% with 50-70% reduction in CYTB5R activity. Spectroscopic analysis of the hemolysate showed normal peaks suggesting the absence of Hb-M. Molecular characterization showed a novel homozygous mutation p.Arg192Cys in CYB5R3 gene is an evolutionarily conserved position located in exon 7 in all eight index cases. The substitution of Cys is located on the interface of two domains of NADH-binding domain and is close proximity to the adenosine moiety would preclude the reciprocal ionic interaction (salt bridge) between Arg192 and Ile97 and may influence binding of the NADH coenzyme is hypothesized to cause disruption of hydrogen bonding and instability. Our study indicated that novel homozygous mutation p.Arg192Cys in CYB5R3 gene present in eight cases and the possibility of high prevalence of heterozygous in Indian population causing Type I RCM.

Clinical, metabolic, and molecular genetic characterization of hereditary methemoglobinemia caused by cytochrome b5 reductase deficiency in 30 dogs

“…Presumably, the proline substitution at position 218 or 219 in the enzyme exerts the same negative effect on protein function. The Ile194Leu and Thr202Ala substitutions have not been observed previously in humans with CYB5R deficiency; however, nearby amino acid substitutions (Arg192Cys and Cys204Arg) are associated with methemoglobinemia in humans 21,26 .…”

“…Median erythrocyte CYB5R enzyme activity in dogs with CYB5R deficiency was 10.9% (IQR, 5.0-24.1; n = 27). The correlation between Hb concentration and both log transformed MetHb (r[20] = 0.18, P = 0.40) and log transformed CYB5R enzyme activity (r [21] = − 0.13, P = 0.56) was weak and not significant, however, there was a negative correlation between log transformed MetHb and log transformed CYB5R enzyme activity (r [25] = − 0.51, P = 0.006).…”

“…The other two variants were each only seen in a single mixed-breed dog and thus may be rare or private variants. Hereditary methemoglobinemia due to CYB5R deficiency is an autosomal recessive trait in all species studied 21,22 . Thus, we expected to find biallelic variants in all of the affected dogs.…”

Clinical, metabolic, and genetic characterization of hereditary methemoglobinemia caused by cytochrome b5reductase deficiency in cats

“…Methemoglobinemia can be acquired or have a hereditary cause. Hereditary methemoglobinemia in dogs and cats, like people, is most commonly caused by CYB5R deficiency. Both cats of this report had markedly reduced CYB5R activity in their erythrocytes.…”

Mutation update: Variants of the CYB5R3 gene in recessive congenital methemoglobinemia

“…(p.Arg192Cys)(Kedar, Gupta, Warang, Chiddarwar, & Madkaikar, 2018), IVS4-2A>G (p.Met127Val)(Kugler, Pekrun, Laspe, Erdlenbruch, & Lakomek, 2001), c.173G>A (Arg58Gln)(Katsube, Sakamoto, Kobayashi, Seki, & Hirano, 1991;Percy et al, 2005;Shirabe et al, 1992;Wang et al, 2000;Warang, Kedar, Shanmukaiah, Ghosh, & Colah, 2015a), c.173G>C(Arg58Pro) (Percy et al, 2012), c.653T>C(Leu218Pro) (Nussenzveig et al, 2006), c.176G>A(Arg59His) (Sacco & Trepanier, 2010), c.479G>C (Arg160Pro) (Warang, Kedar, Shanmukaiah, et al, 2015a), c.181C>T (Arg61Cys) (De Geus et al, 2018), c.431G>A (Gly144Asp) (Fermo et al, 2008; Kedar et al, 2018), c.470T>G (Phe157Cys) (Lorenzo et al, 2011) and four novel mutations c.103C>A(Thr35Pro), c.190C>G (Leu64Val), c.310G>T (Gly104Cys), and c.352C>T (His118Tyr). The new mutations affect highly conserved residues were not detected in 1000 Genomes and HGMD databases.…”