ABCMdb

ABCC8 p.Gly296Arg

ClinVar:	c.886G>A , p.Gly296Arg D , Likely pathogenic
Predicted by SNAP2:	A: N (53%), C: D (71%), D: D (71%), E: D (71%), F: D (75%), H: D (80%), I: D (71%), K: N (53%), L: D (75%), M: D (80%), N: D (53%), P: D (63%), Q: D (80%), R: N (53%), S: N (72%), T: N (53%), V: D (75%), W: N (57%), Y: D (75%),
Predicted by PROVEAN:	A: D, C: D, D: D, E: D, F: D, H: D, I: D, K: D, L: D, M: D, N: D, P: D, Q: D, R: D, S: D, T: D, V: D, W: D, Y: D,

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Publications
[hide] Compound heterozygous mutations in the SUR1 (ABCC ... Channels (Austin). 2012 Mar-Apr;6(2):133-8. doi: 10.4161/chan.19980. Epub 2012 Mar 1. Lin YW, Akrouh A, Hsu Y, Hughes N, Nichols CG, De Leon DD
Compound heterozygous mutations in the SUR1 (ABCC 8) subunit of pancreatic K(ATP) channels cause neonatal diabetes by perturbing the coupling between Kir6.2 and SUR1 subunits.
Channels (Austin). 2012 Mar-Apr;6(2):133-8. doi: 10.4161/chan.19980. Epub 2012 Mar 1., [PMID:22562119]

Abstract [show]
KATP channels regulate insulin secretion by coupling beta-cell metabolism to membrane excitability. These channels are comprised of a pore-forming Kir6.2 tetramer which is enveloped by four regulatory SUR1 subunits. ATP acts on Kir6.2 to stabilize the channel closed state while ADP (coordinated with Mg(2+)) activates channels via the SUR1 domains. Aberrations in nucleotide-binding or in coupling binding to gating can lead to hyperinsulinism or diabetes. Here, we report a case of diabetes in a 7-mo old child with compound heterozygous mutations in ABCC8 (SUR1[A30V] and SUR1[G296R]). In unison, these mutations lead to a gain of KATP channel function, which will attenuate the beta-cell response to increased metabolism and will thereby decrease insulin secretion. (86)Rb(+) flux assays on COSm6 cells coexpressing the mutant subunits (to recapitulate the compound heterozygous state) show a 2-fold increase in basal rate of (86)Rb(+) efflux relative to WT channels. Experiments on excised inside-out patches also reveal a slight increase in activity, manifested as an enhancement in stimulation by MgADP in channels expressing the compound heterozygous mutations or homozygous G296R mutation. In addition, the IC 50 for ATP inhibition of homomeric A30V channels was increased ~6-fold, and was increased ~3-fold for both heteromeric A30V+WT channels or compound heterozygous (A30V +G296R) channels. Thus, each mutation makes a mechanistically distinct contribution to the channel gain-of-function that results in neonatal diabetes, and which we predict may contribute to diabetes in related carrier individuals.

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No. Sentence Comment
8 Here, we report a case of diabetes in a 7-mo old child with compound heterozygous mutations in ABCC8 (SUR1[A30V] and SUR1[G296R]). Login to comment
11 Experiments on excised inside-out patches also reveal a slight increase in activity, manifested as an enhancement in stimulation by MgADP in channels expressing the compound heterozygous mutations or homozygous G296R mutation. Login to comment
12 In addition, the IC50 for ATP inhibition of homomeric A30V channels was increased ~6-fold, and was increased ~3-fold for both heteromeric A30V + WT channels or compound heterozygous (A30V + G296R) channels. Login to comment
32 Direct sequencing of his DNA revealed two mutations in the ABCC8 gene c.886 G > A (G296R) and c.89 C > T (A30V), the first of which is maternally derived and the second is paternally derived. Login to comment
41 As shown in Figure 1A, neither heteromeric single mutant channels ([A30V + WT], referred to as hetA30V and [G296R + WT], referred to as hetG296R) nor compound heterozygous channels ([A30V + G296R]) exhibited significantly different maximum 86 Rb+ efflux rates in the presence of metabolic inhibitors. Login to comment
53 k2,basal /k2,MI calculated from WT, het A30V, het G296R and SUR1[A30V + G296R] are 0.07 &#b1; 0.005, 0.08 &#b1; 0.01, 0.1 &#b1; 0.01 and 0.16 &#b1; 0.01 (n = 4-9). Login to comment
56 Homozygous G296R channels exhibit a slightly right-shifted dose-response, but homozygous A30V channels exhibit a marked and significantly right-shifted ATP sensitivity (Fig. 4B). Login to comment
57 In the heteromeric case, mimicking the disease condition, hetG296R channels are not markedly different from WT, but hetA30V and compound heterozygous A30V + G296R channels both exhibit a significant rightward shift when compared with WT channels (Fig. 4C). Login to comment
64 A30V and G296R mutants are located at the TMD0 and the cytosolic linker region (L0) of SUR1 3 (Fig. 2). Login to comment
66 Here we characterized the sensitivity to MgADP activation, as well as inhibitory ATP sensitivity (without Mg2+ ), of homomeric A30V channels (labeled as homA30V), homomeric G296R channels (labeled as homG296R), hetA30V, hetG296R and compound heterozygous channels [A30V + G296R].8,18,19 Representative recordings of channel response to MgADP from WT and compound heterozygous mutants are shown in Figure 3A and summary results are shown in Figure 3B. Login to comment
67 Homomeric G296R channels exhibit dramatically increased MgADP activity, while homomeric A30V channels show no significant enhancement (Fig. 3B). Login to comment
75 The red filled circles indicate the predicted positions for A30V at the N terminus of its 1st transmembrane domain (TMD0) and G296R at the L0 linker region before TMD1 domain. Login to comment
79 Representative inside-out patch clamp recordings of WT and A30V + G296R in different MgATP and MgADP concentrations (A). Login to comment
81 (B) Relative channel currents in 0.1 mM MgATP and plus 0.5 mM MgADP for WT, homA30V, homG296R, hetA30V, hetG296R and compound heterozygous [A30V + G296R] channels as indicated. Login to comment
85 Interestingly, the G296R variant was identified as a rare variant in whole exome sequencing of over 1,000 individuals (http://evs. Login to comment
90 Although the standard definition of neonatal diabetes refers to diabetes presenting in the first 6 mo of life,20 not uncommonly, like in our case, presentation is beyond this age, prompting some to propose to replace the term "neonatal diabetes mellitus" with "diabetes mellitus of infancy".21 Each ABCC8 mutation carried by this child makes a unique contribution to enhancement of channel activity, resulting in marked stimulation of basal Rb efflux only in the compound heterozygous case (Fig. 1B and C), and explaining the presentation of the disease in the proband, as well as the responsivity to sulfonylureas.22,23 The G296R mutation is inherited from the Figure 4. Login to comment
92 (A) Representative currents recorded by inside-out excised patch-clamp technique from COSm6 cells expressing WT, homA30V, homG296R and [A30V + G296R] at +50 mV pipette potential. Patches were exposed to different concentrations of Mg-free ATP as indicated. Login to comment
96 Fitted K1/2 for WT, homA30V and homG296R channels are 9.65, 53.31 and 28.11 (in bc;M) and the Hill coefficients are 1.22, 1.04 and 1.19, respectively. (C) The fitted K1/2 for WT, hetA30V, hetG296R and [A30V + G296R] are 9.65, 25.75, 12.75 and 25.45 (in bc;M) and the Hill coefficients are 1.22, 1.28, 1.29 and 1.23, respectively. from the child and both parents. Login to comment
98 Two mutations were found in ABCC8 in the proband: c.886 G > A, predicted to cause a G296R amino acid change, was maternally transmitted, and c.89 C > T, predicted to cause A30V amino acid change, was paternally transmitted. Login to comment
125 (A) Representative currents recorded by inside-out excised patch-clamp technique from COSm6 cells expressing WT and [A30V + G296R] at +50 mV pipette potential. Patches were exposed to different concentrations of glibenclamide as indicated (free Mg-nucleotide). Login to comment