16-8768905-C-G

Variant names:

• chr16-8768905-C-G
• rs201397255
• NM_020686.6:c.748C>G

Variant summary

Our verdict is Uncertain significance. Variant got 2 ACMG points: 2P and 0B. PM2

The NM_020686.6(ABAT):​c.748C>G​(p.Arg250Gly) variant causes a missense change involving the alteration of a non-conserved nucleotide. The variant allele was found at a frequency of 0.00000342 in 1,461,882 control chromosomes in the GnomAD database, with no homozygous occurrence. Variant has been reported in ClinVar as Uncertain significance (★).

• Frequency:
  • Genomes: not found (cov: 33)
  • Exomes 𝑓: 0.0000034 (0 hom.)
• Consequence: ABAT NM_020686.6 missense
• Clinical Significance: Uncertain significance criteria provided, single submitter U:1
• Conservation: PhyloP100: 2.32

Genes affected

ABAT (HGNC:23): (4-aminobutyrate aminotransferase) 4-aminobutyrate aminotransferase (ABAT) is responsible for catabolism of gamma-aminobutyric acid (GABA), an important, mostly inhibitory neurotransmitter in the central nervous system, into succinic semialdehyde. The active enzyme is a homodimer of 50-kD subunits complexed to pyridoxal-5-phosphate. The protein sequence is over 95% similar to the pig protein. GABA is estimated to be present in nearly one-third of human synapses. ABAT in liver and brain is controlled by 2 codominant alleles with a frequency in a Caucasian population of 0.56 and 0.44. The ABAT deficiency phenotype includes psychomotor retardation, hypotonia, hyperreflexia, lethargy, refractory seizures, and EEG abnormalities. Multiple alternatively spliced transcript variants encoding the same protein isoform have been found for this gene. [provided by RefSeq, Jul 2008]

ACMG classification

Verdict is Uncertain_significance. Variant got 2 ACMG points.

• PM2: Very rare variant in population databases, with high coverage

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	MANE	Protein	UniProt
ABAT	NM_020686.6	c.748C>G	p.Arg250Gly	missense_variant	Exon 11 of 16	ENST00000268251.13	NP_065737.2

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
ABAT	ENST00000268251.13	c.748C>G	p.Arg250Gly	missense_variant	Exon 11 of 16	1	NM_020686.6	ENSP00000268251.8

Frequencies

GnomAD3 genomes Cov.: 33

GnomAD4 exome AF: 0.00000342 AC: 5 AN: 1461882 Hom.: 0 Cov.: 32 AF XY: 0.00000275 AC XY: 2 AN XY: 727244

Gnomad4 AFR exome AF: 0.00

Gnomad4 AMR exome AF: 0.00

Gnomad4 ASJ exome AF: 0.00

Gnomad4 EAS exome AF: 0.0000252

Gnomad4 SAS exome AF: 0.00

Gnomad4 FIN exome AF: 0.00

Gnomad4 NFE exome AF: 0.00000360

Gnomad4 OTH exome AF: 0.00

GnomAD4 genome Cov.: 33

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:1

Revision: criteria provided, single submitter

Submissions by phenotype

Gamma-aminobutyric acid transaminase deficiency Uncertain:1

May 12, 2022

Labcorp Genetics (formerly Invitae), Labcorp

Significance: Uncertain significance

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Algorithms developed to predict the effect of sequence changes on RNA splicing suggest that this variant may create or strengthen a splice site. In summary, the available evidence is currently insufficient to determine the role of this variant in disease. Therefore, it has been classified as a Variant of Uncertain Significance. Algorithms developed to predict the effect of missense changes on protein structure and function are either unavailable or do not agree on the potential impact of this missense change (SIFT: "Deleterious"; PolyPhen-2: "Benign"; Align-GVGD: "Class C0"). This variant has not been reported in the literature in individuals affected with ABAT-related conditions. This variant is not present in population databases (gnomAD no frequency). This sequence change replaces arginine, which is basic and polar, with glycine, which is neutral and non-polar, at codon 250 of the ABAT protein (p.Arg250Gly). -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Benign	0.17
BayesDel_addAF	Pathogenic	0.21	D
BayesDel_noAF	Uncertain	0.060
CADD	Uncertain	25
DANN	Uncertain	0.99
DEOGEN2	Uncertain	0.56	D;D;.;D;D
Eigen	Benign	-0.12
Eigen_PC	Benign	-0.0045
FATHMM_MKL	Uncertain	0.86	D
LIST_S2	Pathogenic	0.98	.;D;D;.;D
M_CAP	Benign	0.079	D
MetaRNN	Uncertain	0.72	D;D;D;D;D
MetaSVM	Benign	-0.54	T
MutationAssessor	Benign	0.86	L;L;.;L;.
PrimateAI	Uncertain	0.67	T
PROVEAN	Uncertain	-3.8	D;D;D;D;D
REVEL	Uncertain	0.60
Sift	Benign	0.096	T;T;T;T;T
Sift4G	Benign	0.15	T;T;T;T;T
Polyphen		0.43	B;B;.;B;.
Vest4		0.76
MutPred		0.47		Loss of catalytic residue at R250 (P = 0.0311);Loss of catalytic residue at R250 (P = 0.0311);.;Loss of catalytic residue at R250 (P = 0.0311);Loss of catalytic residue at R250 (P = 0.0311);
MVP		0.78
MPC		0.44
ClinPred		0.96	D
GERP RS		3.5
Varity_R		0.66
gMVP		0.86

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.21		Details are displayed if max score is > 0.2
DS_AG_spliceai		0.21		Position offset: 1

Find out detailed SpliceAI scores and Pangolin per-transcript scores at spliceailookup.broadinstitute.org

Publications

LitVar

Other links and lift over

dbSNP: rs201397255; hg19: chr16-8862762;