chr16-8768220-C-T

Position:

• chr16-8768220-C-T

Variant summary

Our verdict is Pathogenic. Variant got 12 ACMG points: 12P and 0B. PM2 PP3_Moderate PP5_Very_Strong

The NM_020686.6(ABAT):​c.631C>T​(p.Leu211Phe) variant causes a missense change involving the alteration of a non-conserved nucleotide. The variant allele was found at a frequency of 0.00000205 in 1,461,846 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a pathogenic outcome for this variant. Variant has been reported in ClinVar as Likely pathogenic (★★).

• Frequency:
  • Genomes: not found (cov: 32)
  • Exomes 𝑓: 0.0000021 (0 hom.)
• Consequence: ABAT NM_020686.6 missense
• Clinical Significance: Pathogenic/Likely pathogenic criteria provided, multiple submitters, no conflicts P:3
• Conservation: PhyloP100: 2.67

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 Pathogenic. Variant got 12 ACMG points.

• PM2: Very rare variant in population databases, with high coverage
• PP3: MetaRNN computational evidence supports a deleterious effect, 0.898
• PP5: Variant 16-8768220-C-T is Pathogenic according to our data. Variant chr16-8768220-C-T is described in ClinVar as [Likely_pathogenic]. Clinvar id is 162034.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars. Variant chr16-8768220-C-T is described in Lovd as [Pathogenic].

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
ABAT	NM_020686.6	c.631C>T	p.Leu211Phe	missense_variant	10/16	ENST00000268251.13	NP_065737.2

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
ABAT	ENST00000268251.13	c.631C>T	p.Leu211Phe	missense_variant	10/16	1	NM_020686.6	ENSP00000268251	P1

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome AF: 0.00000205 AC: 3 AN: 1461846 Hom.: 0 Cov.: 31 AF XY: 0.00000275 AC XY: 2 AN XY: 727222

Gnomad4 AFR exome AF: 0.0000299

Gnomad4 AMR exome AF: 0.00

Gnomad4 ASJ exome AF: 0.00

Gnomad4 EAS exome AF: 0.00

Gnomad4 SAS exome AF: 0.00

Gnomad4 FIN exome AF: 0.00

Gnomad4 NFE exome AF: 0.00000180

Gnomad4 OTH exome AF: 0.00

GnomAD4 genome Cov.: 32

ClinVar

Significance: Pathogenic/Likely pathogenic

Submissions summary: Pathogenic:3

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Gamma-aminobutyric acid transaminase deficiency Pathogenic:3

Pathogenic, criteria provided, single submitter	clinical testing	Elsea Laboratory, Baylor College of Medicine	Feb 01, 2019	- -
Pathogenic, criteria provided, single submitter	research	Bonnen Lab, Baylor College of Medicine	Jan 01, 2014	clinical and in vitro studies -
Likely pathogenic, criteria provided, single submitter	clinical testing	Labcorp Genetics (formerly Invitae), Labcorp	Oct 03, 2023	This sequence change replaces leucine, which is neutral and non-polar, with phenylalanine, which is neutral and non-polar, at codon 211 of the ABAT protein (p.Leu211Phe). This variant is not present in population databases (gnomAD no frequency). This missense change has been observed in individual(s) with GABA-transaminase deficiency (PMID: 25738457, 27903293, 29302074). It has also been observed to segregate with disease in related individuals. ClinVar contains an entry for this variant (Variation ID: 162034). Advanced modeling of protein sequence and biophysical properties (such as structural, functional, and spatial information, amino acid conservation, physicochemical variation, residue mobility, and thermodynamic stability) performed at Invitae indicates that this missense variant is expected to disrupt ABAT protein function. Experimental studies have shown that this missense change affects ABAT function (PMID: 25738457, 27903293). In summary, the currently available evidence indicates that the variant is pathogenic, but additional data are needed to prove that conclusively. Therefore, this variant has been classified as Likely Pathogenic. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Pathogenic	0.74
BayesDel_addAF	Pathogenic	0.41	D
BayesDel_noAF	Pathogenic	0.35
CADD	Pathogenic	27
DANN	Pathogenic	1.0
DEOGEN2	Uncertain	0.68	D;D;.;D;D
Eigen	Pathogenic	0.87
Eigen_PC	Pathogenic	0.79
FATHMM_MKL	Uncertain	0.84	D
LIST_S2	Pathogenic	0.99	.;D;D;.;D
M_CAP	Uncertain	0.20	D
MetaRNN	Pathogenic	0.90	D;D;D;D;D
MetaSVM	Pathogenic	0.90	D
MutationAssessor	Pathogenic	3.4	M;M;.;M;.
MutationTaster	Benign	1.0	D;D;D;D;D
PrimateAI	Pathogenic	0.81	D
PROVEAN	Uncertain	-3.6	D;D;D;D;D
REVEL	Pathogenic	0.82
Sift	Uncertain	0.0020	D;D;D;D;D
Sift4G	Uncertain	0.0050	D;D;D;D;D
Polyphen		1.0	D;D;.;D;.
Vest4		0.84
MutPred		0.71		Gain of catalytic residue at L211 (P = 0.0227);Gain of catalytic residue at L211 (P = 0.0227);.;Gain of catalytic residue at L211 (P = 0.0227);Gain of catalytic residue at L211 (P = 0.0227);
MVP		0.91
MPC		1.1
ClinPred		0.99	D
GERP RS		5.6
Varity_R		0.89
gMVP		0.89

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.0		Details are displayed if max score is > 0.2

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

Publications

LitVar

Other links and lift over

dbSNP: rs724159990; hg19: chr16-8862077; COSMIC: COSV99190889;