rs776631396

chr6-80167744-C-Achr6-80167744-C-T

Variant summary

Our verdict is Pathogenic. Variant got 11 ACMG points: 11P and 0B. PM1 PM2 PM5 PP3_Strong PP5

The NM_183050.4(BCKDHB):c.410C>A(p.Ala137Glu) variant causes a missense change involving the alteration of a conserved nucleotide. The variant allele was found at a frequency of 0.00000137 in 1,460,684 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a pathogenic outcome for this variant. 12/20 in silico tools predict a damaging outcome for this variant. Variant has been reported in ClinVar as Conflicting classifications of pathogenicity (no stars). Another variant affecting the same amino acid position, but resulting in a different missense (i.e. A137V) has been classified as Likely pathogenic.

• Frequency:
  • Genomes: not found (cov: 31)
  • Exomes 𝑓: 0.0000014 (0 hom.)
• Consequence: BCKDHB NM_183050.4 missense
• Clinical Significance: Conflicting classifications of pathogenicity criteria provided, conflicting classifications P:1 U:2
• Conservation: PhyloP100: 7.55

Genes affected

BCKDHB (HGNC:987): (branched chain keto acid dehydrogenase E1 subunit beta) This gene encodes the E1 beta subunit of branched-chain keto acid dehydrogenase, which is a multienzyme complex associated with the inner membrane of mitochondria. This enzyme complex functions in the catabolism of branched-chain amino acids. Mutations in this gene have been associated with maple syrup urine disease (MSUD), type 1B, a disease characterized by a maple syrup odor to the urine in addition to mental and physical retardation and feeding problems. Alternative splicing at this locus results in multiple transcript variants. [provided by RefSeq, Jan 2016]

ACMG classification

Verdict is Pathogenic. Variant got 11 ACMG points.

• PM1: In a hotspot region, there are 3 aminoacids with missense pathogenic changes in the window of +-8 aminoacids around while only 0 benign, 3 uncertain in NM_183050.4
• PM2: Very rare variant in population databases, with high coverage
• PM5: Other missense variant is known to change same aminoacid residue: Variant chr6-80167744-C-T is described in ClinVar as [Likely_pathogenic]. Clinvar id is 370949.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars.
• PP3: MetaRNN computational evidence supports a deleterious effect, 0.989
• PP5: Variant 6-80167744-C-A is Pathogenic according to our data. Variant chr6-80167744-C-A is described in ClinVar as [Conflicting_classifications_of_pathogenicity]. Clinvar id is 1027626.We mark this variant Likely_pathogenic, oryginal submissions are: {Uncertain_significance=2, Pathogenic=1}.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	UniProt
BCKDHB	NM_183050.4	c.410C>A	p.Ala137Glu	missense_variant	4/10	ENST00000320393.9

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Appris	UniProt
BCKDHB	ENST00000320393.9	c.410C>A	p.Ala137Glu	missense_variant	4/10	1	NM_183050.4	P1
BCKDHB	ENST00000356489.9	c.410C>A	p.Ala137Glu	missense_variant	4/11	1		P1
BCKDHB	ENST00000369760.8	c.410C>A	p.Ala137Glu	missense_variant	4/6	3

Frequencies

GnomAD3 genomes Cov.: 31

GnomAD4 exome AF: 0.00000137 AC: 2 AN: 1460684 Hom.: 0 Cov.: 31 AF XY: 0.00000275 AC XY: 2 AN XY: 726722

Gnomad4 AFR exome AF: 0.00

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: 0.0000187

Gnomad4 NFE exome AF: 9.00e-7

Gnomad4 OTH exome AF: 0.00

GnomAD4 genome Cov.: 31

ClinVar

Significance: Conflicting classifications of pathogenicity

Submissions summary: Pathogenic:1 Uncertain:2

Revision: criteria provided, conflicting classifications

Submissions by phenotype

Maple syrup urine disease Pathogenic:1 Uncertain:1

Pathogenic, criteria provided, single submitter	clinical testing	Invitae	May 13, 2020	For these reasons, this variant has been classified as Pathogenic. This variant disrupts the p.Ala137 amino acid residue in BCKDHB. Other variant(s) that disrupt this residue have been determined to be pathogenic (PMID: 14567968, 16468966, 26830710, 29306928). This suggests that this residue is clinically significant, and that variants that disrupt this residue are likely to be disease-causing. Algorithms developed to predict the effect of missense changes on protein structure and function (SIFT, PolyPhen-2, Align-GVGD) all suggest that this variant is likely to be disruptive, but these predictions have not been confirmed by published functional studies and their clinical significance is uncertain. This variant has been observed in individual(s) with maple syrup urine disease (Invitae). In at least one individual the data is consistent with the variant being in trans (on the opposite chromosome) from a pathogenic variant. This variant is not present in population databases (ExAC no frequency). This sequence change replaces alanine with glutamic acid at codon 137 of the BCKDHB protein (p.Ala137Glu). The alanine residue is highly conserved and there is a moderate physicochemical difference between alanine and glutamic acid. -
Uncertain significance, criteria provided, single submitter	clinical testing	Genome-Nilou Lab	Nov 07, 2021	- -

not specified Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Women's Health and Genetics/Laboratory Corporation of America, LabCorp

Mar 06, 2023

Variant summary: BCKDHB c.410C>A (p.Ala137Glu) results in a non-conservative amino acid change located in the Transketolase-like, pyrimidine-binding domain (IPR005475) of the encoded protein sequence. Five of five in-silico tools predict a damaging effect of the variant on protein function. The variant was absent in 251162 control chromosomes (gnomAD). To our knowledge, no occurrence of c.410C>A in individuals affected with Maple Syrup Urine Disease and no experimental evidence demonstrating its impact on protein function have been reported. A different variant at the same codon position has been reported in association with Maple Syrup Urine Disease in HGMD (c.410C>T, p.Ala137Val). Two clinical diagnostic laboratories have submitted clinical-significance assessments for this variant to ClinVar after 2014 and classified the variant as pathogenic, and one laboratory classified the variant as uncertain significance. Based on the evidence outlined above, the variant was classified as VUS-possibly pathogenic. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Pathogenic	0.99
BayesDel_addAF	Pathogenic	0.57	D
BayesDel_noAF	Pathogenic	0.58
Cadd	Pathogenic	29
Dann	Uncertain	0.99
Eigen	Pathogenic	0.99
Eigen_PC	Pathogenic	0.80
FATHMM_MKL	Pathogenic	0.98	D
LIST_S2	Pathogenic	0.99	D;.;D
M_CAP	Pathogenic	0.68	D
MetaRNN	Pathogenic	0.99	D;D;D
MetaSVM	Pathogenic	1.0	D
MutationAssessor	Pathogenic	4.7	H;H;H
MutationTaster	Benign	1.0	D;D;D;D
PrimateAI	Pathogenic	0.80	T
PROVEAN	Pathogenic	-4.6	D;D;D
REVEL	Pathogenic	0.96
Sift	Pathogenic	0.0	D;D;D
Sift4G	Pathogenic	0.0	D;D;D
Polyphen		1.0	.;D;D
Vest4		0.96
MutPred		0.85		Loss of helix (P = 0.079);Loss of helix (P = 0.079);Loss of helix (P = 0.079);
MVP		0.99
MPC		0.84
ClinPred		1.0	D
GERP RS		4.8
RBP_binding_hub_radar		0.0
RBP_regulation_power_radar		1.7
Varity_R		0.98
gMVP		1.0

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: rs776631396; hg19: chr6-80877461;