6-80273178-C-T

Position:

• chr6-80273178-C-T

Variant summary

Our verdict is Uncertain significance. Variant got 5 ACMG points: 5P and 0B. PM2 PP3_Moderate PP5

The NM_183050.4(BCKDHB):​c.995C>T​(p.Pro332Leu) variant causes a missense change. The variant was absent in control chromosomes in GnomAD project. In-silico tool predicts a pathogenic outcome for this variant. Variant has been reported in ClinVar as Conflicting classifications of pathogenicity (no stars).

• Frequency: Genomes: not found (cov: 33)
• Consequence: BCKDHB NM_183050.4 missense
• Clinical Significance: Conflicting classifications of pathogenicity criteria provided, conflicting classifications P:6 U:2
• Conservation: PhyloP100: 4.79

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 Uncertain_significance. Variant got 5 ACMG points.

• PM2: Very rare variant in population databases, with high coverage
• PP3: MetaRNN computational evidence supports a deleterious effect, 0.911
• PP5: Variant 6-80273178-C-T is Pathogenic according to our data. Variant chr6-80273178-C-T is described in ClinVar as [Conflicting_classifications_of_pathogenicity]. Clinvar id is 432059.We mark this variant Likely_pathogenic, oryginal submissions are: {Likely_pathogenic=5, Uncertain_significance=2, Pathogenic=1}. Variant chr6-80273178-C-T is described in Lovd as [Likely_pathogenic].

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
BCKDHB	NM_183050.4	c.995C>T	p.Pro332Leu	missense_variant	9/10	ENST00000320393.9	NP_898871.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
BCKDHB	ENST00000320393.9	c.995C>T	p.Pro332Leu	missense_variant	9/10	1	NM_183050.4	ENSP00000318351	P1
BCKDHB	ENST00000356489.9	c.995C>T	p.Pro332Leu	missense_variant	9/11	1		ENSP00000348880	P1
BCKDHB	ENST00000468520.1	n.225C>T		non_coding_transcript_exon_variant	3/3	5

Frequencies

GnomAD3 genomes Cov.: 33

GnomAD4 exome Cov.: 30

GnomAD4 genome Cov.: 33

ClinVar

Significance: Conflicting classifications of pathogenicity

Submissions summary: Pathogenic:6 Uncertain:2

Revision: criteria provided, conflicting classifications

Submissions by phenotype

Maple syrup urine disease Pathogenic:4 Uncertain:1

Uncertain significance, criteria provided, single submitter	clinical testing	Counsyl	Apr 20, 2018	- -
Pathogenic, criteria provided, single submitter	clinical testing	Labcorp Genetics (formerly Invitae), Labcorp	Apr 11, 2023	For these reasons, this variant has been classified as Pathogenic. 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 BCKDHB protein function. ClinVar contains an entry for this variant (Variation ID: 432059). This missense change has been observed in individual(s) with maple syrup urine disease (MSUD) (Invitae; http//d-nb.info/1009923471/34). This variant is not present in population databases (gnomAD no frequency). This sequence change replaces proline, which is neutral and non-polar, with leucine, which is neutral and non-polar, at codon 332 of the BCKDHB protein (p.Pro332Leu). -
Likely pathogenic, criteria provided, single submitter	clinical testing	Laboratorio de Genetica e Diagnostico Molecular, Hospital Israelita Albert Einstein	Nov 10, 2022	ACMG classification criteria: PM2 moderated, PM3 moderated, PP3 supporting, PP4 -
Likely pathogenic, criteria provided, single submitter	clinical testing	Baylor Genetics	Feb 10, 2023	- -
Likely pathogenic, criteria provided, single submitter	clinical testing	Genome-Nilou Lab	Nov 07, 2021	- -

not provided Pathogenic:2

Likely pathogenic, criteria provided, single submitter	clinical testing	GeneDx	Jan 25, 2016	The P332L variant has not been published as a pathogenic variant, nor has it been reported as a benign variant to our knowledge. The P332L variant was not observed in approximately 6500 individuals of European and African American ancestry in the NHLBI Exome Sequencing Project, indicating it is not a common benign variant in these populations. The P332L variant is a semi-conservative amino acid substitution, which may impact secondary protein structure as these residues differ in some properties. This substitution occurs at a position that is conserved across species. In silico analysis predicts this variant is probably damaging to the protein structure/function. Therefore, this variant is likely pathogenic; however, the possibility that it is benign cannot be excluded. -
Likely pathogenic, criteria provided, single submitter	clinical testing	CeGaT Center for Human Genetics Tuebingen	Jul 01, 2024	BCKDHB: PM1, PM2, PM3, PP4:Moderate -

BCKDHB-related disorder Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

PreventionGenetics, part of Exact Sciences

Jul 13, 2023

The BCKDHB c.995C>T variant is predicted to result in the amino acid substitution p.Pro332Leu. This variant has been reported in the homozygous state in an individual with Maple syrup urine disease (Table 2, Nair et al. 2018. PubMed ID: 30293248; Table 3, Khalifa et al. 2020. PubMed ID: 32812330). This variant has not been reported in a large population database (http://gnomad.broadinstitute.org), indicating this variant is rare. While we suspect that this variant is pathogenic, at this time its clinical significance is uncertain due to the absence of conclusive functional and genetic evidence. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Pathogenic	0.70
BayesDel_addAF	Pathogenic	0.41	D
BayesDel_noAF	Pathogenic	0.35
CADD	Pathogenic	30
DANN	Uncertain	1.0
DEOGEN2	Uncertain	0.71	D;D
Eigen	Pathogenic	0.89
Eigen_PC	Pathogenic	0.81
FATHMM_MKL	Pathogenic	0.98	D
LIST_S2	Pathogenic	0.99	.;D
M_CAP	Pathogenic	0.30	D
MetaRNN	Pathogenic	0.91	D;D
MetaSVM	Pathogenic	0.95	D
MutationAssessor	Pathogenic	3.7	H;H
MutationTaster	Benign	1.0	D;D;D
PrimateAI	Uncertain	0.69	T
PROVEAN	Pathogenic	-8.5	D;D
REVEL	Pathogenic	0.78
Sift	Uncertain	0.0080	D;D
Sift4G	Uncertain	0.039	D;D
Polyphen		1.0	D;D
Vest4		0.95
MutPred		0.49		Loss of disorder (P = 0.0412);Loss of disorder (P = 0.0412);
MVP		0.99
MPC		0.74
ClinPred		1.0	D
GERP RS		5.7
Varity_R		0.93
gMVP		0.89

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.010		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: rs1554205541; hg19: chr6-80982895; COSMIC: COSV105204899;