6-80168900-G-C

Variant names:

• chr6-80168900-G-C
• rs749033513
• NM_183050.4:c.503G>C

Variant summary

Our verdict is Pathogenic. The variant received 11 ACMG points: 11P and 0B. PM1 PM2 PM5 PP2 PP3_Strong

The NM_183050.4(BCKDHB):​c.503G>C​(p.Arg168Pro) variant causes a missense change involving the alteration of a conserved nucleotide. The variant allele was found at a frequency of 0.00000186 in 1,613,956 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a pathogenic outcome for this variant. 13/22 in silico tools predict a damaging outcome for this variant. Variant has been reported in ClinVar as Uncertain significance (★). Another variant affecting the same amino acid position, but resulting in a different missense (i.e. R168C) has been classified as Pathogenic.

• Frequency:
  • Genomes: 𝑓 0.0000066 (0 hom., cov: 32)
  • Exomes 𝑓: 0.0000014 (0 hom.)
• Consequence: BCKDHB NM_183050.4 missense
• Clinical Significance: Uncertain significance criteria provided, single submitter U:1
• Conservation: PhyloP100: 9.49
• Publications: 3 publications found

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]

BCKDHB Gene-Disease associations (from GenCC):

• maple syrup urine disease type 1B

  Inheritance: AR Classification: DEFINITIVE Submitted by: ClinGen, G2P, Myriad Women’s Health
• maple syrup urine disease

  Inheritance: AR Classification: STRONG Submitted by: Labcorp Genetics (formerly Invitae)
• classic maple syrup urine disease

  Inheritance: AR Classification: SUPPORTIVE Submitted by: Orphanet
• intermediate maple syrup urine disease

  Inheritance: AR Classification: SUPPORTIVE Submitted by: Orphanet
• intermittent maple syrup urine disease

  Inheritance: AR Classification: SUPPORTIVE Submitted by: Orphanet
• thiamine-responsive maple syrup urine disease

  Inheritance: AR Classification: SUPPORTIVE Submitted by: Orphanet

ACMG classification

Our verdict: Pathogenic. The variant received 11 ACMG points.

• PM1: In a hotspot region, there are 12 aminoacids with missense pathogenic changes in the window of +-8 aminoacids around while only 0 benign, 4 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 chr6-80168899-C-T is described in ClinVar as Conflicting_classifications_of_pathogenicity. ClinVar VariationId is 96586.
• PP2: Missense variant in the gene, where a lot of missense mutations are associated with disease in ClinVar. The gene has 51 curated pathogenic missense variants (we use a threshold of 10). The gene has 5 curated benign missense variants. Gene score misZ: -0.17637 (below the threshold of 3.09). Trascript score misZ: -0.0026186 (below the threshold of 3.09). GenCC associations: The gene is linked to classic maple syrup urine disease, thiamine-responsive maple syrup urine disease, intermittent maple syrup urine disease, intermediate maple syrup urine disease, maple syrup urine disease type 1B, maple syrup urine disease.
• PP3: MetaRNN computational evidence supports a deleterious effect, 0.988

Variant Effect in Transcripts

ACMG analysis was done for transcript: NM_183050.4. You can select a different transcript below to see updated ACMG assignments.

RefSeq Transcripts

Selected	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	BCKDHB	NM_183050.4	MANE Select	c.503G>C	p.Arg168Pro	missense	Exon 5 of 10	NP_898871.1
	BCKDHB	NM_001424035.1		c.503G>C	p.Arg168Pro	missense	Exon 5 of 10	NP_001410964.1
	BCKDHB	NM_000056.5		c.503G>C	p.Arg168Pro	missense	Exon 5 of 11	NP_000047.1

Ensembl Transcripts

Selected	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	BCKDHB	ENST00000320393.9	TSL:1 MANE Select	c.503G>C	p.Arg168Pro	missense	Exon 5 of 10	ENSP00000318351.5
	BCKDHB	ENST00000356489.9	TSL:1	c.503G>C	p.Arg168Pro	missense	Exon 5 of 11	ENSP00000348880.5
	BCKDHB	ENST00000369760.8	TSL:3	c.503G>C	p.Arg168Pro	missense	Exon 5 of 6	ENSP00000358775.4

Frequencies

GnomAD3 genomes AF: 0.00000657 AC: 1 AN: 152110 Hom.: 0 Cov.: 32

Gnomad AFR AF: 0.00

Gnomad AMI AF: 0.00

Gnomad AMR AF: 0.00

Gnomad ASJ AF: 0.00

Gnomad EAS AF: 0.00

Gnomad SAS AF: 0.00

Gnomad FIN AF: 0.00

Gnomad MID AF: 0.00

Gnomad NFE AF: 0.0000147

Gnomad OTH AF: 0.00

GnomAD4 exome AF: 0.00000137 AC: 2 AN: 1461846 Hom.: 0 Cov.: 34 AF XY: 0.00000275 AC XY: 2 AN XY: 727224

African (AFR) AF: 0.00 AC: 0 AN: 33480

American (AMR) AF: 0.00 AC: 0 AN: 44724

Ashkenazi Jewish (ASJ) AF: 0.00 AC: 0 AN: 26136

East Asian (EAS) AF: 0.00 AC: 0 AN: 39694

South Asian (SAS) AF: 0.0000116 AC: 1 AN: 86258

European-Finnish (FIN) AF: 0.00 AC: 0 AN: 53420

Middle Eastern (MID) AF: 0.00 AC: 0 AN: 5768

European-Non Finnish (NFE) AF: 8.99e-7 AC: 1 AN: 1111972

Other (OTH) AF: 0.00 AC: 0 AN: 60394

GnomAD4 genome AF: 0.00000657 AC: 1 AN: 152110 Hom.: 0 Cov.: 32 AF XY: 0.00 AC XY: 0 AN XY: 74296

African (AFR) AF: 0.00 AC: 0 AN: 41412

American (AMR) AF: 0.00 AC: 0 AN: 15276

Ashkenazi Jewish (ASJ) AF: 0.00 AC: 0 AN: 3470

East Asian (EAS) AF: 0.00 AC: 0 AN: 5186

South Asian (SAS) AF: 0.00 AC: 0 AN: 4820

European-Finnish (FIN) AF: 0.00 AC: 0 AN: 10600

Middle Eastern (MID) AF: 0.00 AC: 0 AN: 316

European-Non Finnish (NFE) AF: 0.0000147 AC: 1 AN: 68028

Other (OTH) AF: 0.00 AC: 0 AN: 2092

Alfa AF: 0.00 Hom.: 0

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:1

Revision: criteria provided, single submitter

Submissions by phenotype

not specified Uncertain:1

Jun 25, 2025

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

Significance: Uncertain significance

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Variant summary: BCKDHB c.503G>C (p.Arg168Pro) results in a non-conservative amino acid change in the encoded protein sequence. Algorithms developed to predict the effect of missense changes on protein structure and function all suggest that this variant is likely to be disruptive. The variant was absent in 251412 control chromosomes. To our knowledge, no occurrence of c.503G>C in individuals affected with Maple Syrup Urine Disease and no experimental evidence demonstrating its impact on protein function have been reported. Different variants affecting the same codon have been classified as pathogenic by our lab (c.502C>T (p.Arg168Cys), c.503G>A (p.Arg168His)), supporting the critical relevance of codon 168 to BCKDHB protein function. No submitters have cited clinical-significance assessments for this variant to ClinVar. Based on the evidence outlined above, the variant was classified as VUS-possibly pathogenic.

Computational scores

Source: dbNSFP v4.9

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Pathogenic	0.98
BayesDel_addAF	Pathogenic	0.50	D
BayesDel_noAF	Pathogenic	0.48
CADD	Pathogenic	32
DANN	Uncertain	1.0
DEOGEN2	Pathogenic	0.81	D
Eigen	Pathogenic	0.97
Eigen_PC	Pathogenic	0.87
FATHMM_MKL	Pathogenic	0.99	D
LIST_S2	Pathogenic	0.99	D
M_CAP	Pathogenic	0.71	D
MetaRNN	Pathogenic	0.99	D
MetaSVM	Pathogenic	1.1	D
MutationAssessor	Pathogenic	3.4	M
PhyloP100		9.5
PrimateAI	Pathogenic	0.90	D
PROVEAN	Pathogenic	-6.8	D
REVEL	Pathogenic	0.96
Sift	Uncertain	0.013	D
Sift4G	Pathogenic	0.0010	D
Polyphen		1.0	D
Vest4		0.97
MutPred		0.92		Loss of methylation at R170 (P = 0.0946)
MVP		0.99
MPC		0.94
ClinPred		1.0	D
GERP RS		5.1
Varity_R		0.99
gMVP		0.99
Mutation Taster		=3/97	disease causing

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

Other links and lift over

dbSNP: rs749033513; hg19: chr6-80878617;