Mitochondrial complex 2 deficiency, nuclear type 4

Summary

Mitochondrial complex 2 deficiency, nuclear type 4 (MONDO:0030974) is a disease caused by SDHB (GenCC Strong), with 1 cohort gene.

At a glance

• Causal gene: SDHB (GenCC Strong)
• Cohort genes: 1
• ClinVar variants: 50

Clinical features

No curated clinical features (Orphanet) for this disease.

Identifiers

Disease identifiers

Field	Value
Canonical name	mitochondrial complex 2 deficiency, nuclear type 4
Mondo ID	MONDO:0030974
OMIM	619224
UMLS	C5543176
MedGen	1782861
GARD	0016438
Is cancer (heuristic)	no

Also known as: MC2DN4 · mitochondrial complex 2 deficiency, nuclear type 4 · mitochondrial complex II deficiency, nuclear type 4 · SDHB-related Nuclear type mitocondrial complex II deficiency

Data availability: 50 ClinVar variants · 1 GenCC gene-disease record.

Disease family

Classification path: disease › human disease › disease by etiologic mechanism › disease of genetic or genomic mechanism › hereditary disease › autosomal genetic disease › autosomal recessive disease › mitochondrial complex 2 deficiency, nuclear type 4

Related subtypes (218): immunodeficiency-centromeric instability-facial anomalies syndrome, hypercalcemia, infantile, Ochoa syndrome, autosomal recessive Ehlers-Danlos syndrome, vascular type, hydrolethalus syndrome, 3-M syndrome, isolated hyperchlorhidrosis, dacryocystitis-osteopoikilosis syndrome, Hutchinson-Gilford progeria syndrome, achalasia microcephaly syndrome, acrorenal syndrome, autosomal recessive, beta-ketothiolase deficiency, autosomal recessive Alport syndrome, Alstrom syndrome, microphthalmia with limb anomalies, camptodactyly-arthropathy-coxa vara-pericarditis syndrome, Behr syndrome, bifid nose, autosomal recessive, Bloom syndrome, Bowen-Conradi syndrome, camptodactyly with fibrous tissue hyperplasia and skeletal dysplasia, heart defects-limb shortening syndrome, autosomal recessive palmoplantar keratoderma and congenital alopecia, COFS syndrome, craniometaphyseal dysplasia, autosomal recessive, Fraser syndrome, cystic fibrosis, polycystic lipomembranous osteodysplasia with sclerosing leukoencephaly, persistent hyperplastic primary vitreous, autosomal recessive, Donnai-Barrow syndrome, Schöpf-Schulz-Passarge syndrome, cleft lip/palate-ectodermal dysplasia syndrome, Ellis-van Creveld syndrome, Wolcott-Rallison syndrome, autosomal recessive faciodigitogenital syndrome, acromesomelic dysplasia 2B, brittle cornea syndrome, triple-A syndrome, autosomal recessive humeroradial synostosis, multinucleated neurons-anhydramnios-renal dysplasia-cerebellar hypoplasia-hydranencephaly syndrome, hydrocephalus, nonsyndromic, autosomal recessive 1, autosomal recessive hydrocephalus due to congenital stenosis of aqueduct of Sylvius, hypertelorism, microtia, facial clefting syndrome, hypoparathyroidism-retardation-dysmorphism syndrome, Vici syndrome, Johanson-Blizzard syndrome, autosomal recessive Kenny-Caffey syndrome, Papillon-Lefevre disease, Haim-Munk syndrome, Laurence-Moon syndrome, Donohue syndrome, lipase deficiency, combined, autosomal recessive familial Mediterranean fever, thiamine-responsive megaloblastic anemia syndrome, cartilage-hair hypoplasia, Nijmegen breakage syndrome, pseudo-TORCH syndrome, Galloway-Mowat syndrome, mulibrey nanism, myotonia congenita, autosomal recessive, Schwartz-Jampel syndrome, proteosome-associated autoinflammatory syndrome, Netherton syndrome, Niemann-Pick disease type A, oculodentodigital dysplasia, autosomal recessive, odonto-onycho-dermal dysplasia, autosomal recessive omodysplasia, osteoporosis-pseudoglioma syndrome, Shwachman-Diamond syndrome, phenylketonuria, Bjornstad syndrome, Laron syndrome, autosomal recessive polycystic kidney disease, autosomal recessive inherited pseudoxanthoma elasticum, autosomal recessive multiple pterygium syndrome, rapadilino syndrome, short-rib thoracic dysplasia 9 with or without polydactyly, autosomal recessive Robinow syndrome, Sjogren-Larsson syndrome, scapuloperoneal spinal muscular atrophy, autosomal recessive, spondyloepiphyseal dysplasia tarda, autosomal recessive, inherited threoninemia, Pendred syndrome, autosomal recessive spondylocostal dysostosis, Werner syndrome, ABCD syndrome, Naxos disease, autosomal recessive amelia, human HOXA1 syndromes, sickle cell disease, autosomal recessive proximal renal tubular acidosis, hyper-IgM syndrome type 2, temtamy preaxial brachydactyly syndrome, TH-deficient dopa-responsive dystonia, craniosynostosis syndrome, autosomal recessive, Niemann-Pick disease type B, skin fragility-woolly hair-palmoplantar keratoderma syndrome, CoQ-responsive OXPHOS deficiency, familial adenomatous polyposis 2, Pierson syndrome, palmoplantar keratoderma-XX sex reversal-predisposition to squamous cell carcinoma syndrome, cardiomyopathy-hypotonia-lactic acidosis syndrome, PHARC syndrome, Kahrizi syndrome, cutis laxa with severe pulmonary, gastrointestinal and urinary anomalies, congenital prothrombin deficiency, immunodeficiency 31B, dyskeratosis congenita, autosomal recessive 2, dyskeratosis congenita, autosomal recessive 3, Nestor-Guillermo progeria syndrome, leukoencephalopathy with calcifications and cysts, mitochondrial pyruvate carrier deficiency, branched-chain keto acid dehydrogenase kinase deficiency, dyskeratosis congenita, autosomal recessive 5, hypohidrosis-enamel hypoplasia-palmoplantar keratoderma-intellectual disability syndrome, alacrima, achalasia, and intellectual disability syndrome, hyperlipoproteinemia, type 1D, microcephaly and chorioretinopathy 2, congenital stationary night blindness 1G, combined oxidative phosphorylation deficiency 29, hypermanganesemia with dystonia 2, growth retardation, intellectual developmental disorder, hypotonia, and hepatopathy, gnb5-related intellectual disability-cardiac arrhythmia syndrome, autosomal recessive spastic paraplegia type 78, autosomal recessive limb-girdle muscular dystrophy, Bardet-Biedl syndrome, autosomal recessive cerebellar ataxia, neuronopathy, distal hereditary motor, autosomal recessive, UV-sensitive syndrome, Ehlers-Danlos syndrome, kyphoscoliotic type 1, Cockayne syndrome, hyperphenylalaninemia due to tetrahydrobiopterin deficiency, leukoencephalopathy-palmoplantar keratoderma syndrome, autosomal recessive hypohidrotic ectodermal dysplasia, Warburg micro syndrome, autosomal recessive primary microcephaly, autosomal recessive progressive external ophthalmoplegia, Meier-Gorlin syndrome, autosomal recessive sideroblastic anemia, autosomal recessive intermediate Charcot-Marie-Tooth disease, Perrault syndrome, autosomal recessive hypophosphatemic rickets, de Barsy syndrome, leukocyte adhesion deficiency, Senior-Loken syndrome, autosomal recessive spastic ataxia, childhood-onset autosomal recessive myopathy with external ophthalmoplegia, autosomal recessive cerebral atrophy, GM3 synthase deficiency, autosomal recessive distal renal tubular acidosis, pigmentation defects-palmoplantar keratoderma-skin carcinoma syndrome, autosomal recessive brachyolmia, Aicardi-Goutieres syndrome, homocystinuria without methylmalonic aciduria, Niemann-Pick disease type C, nephronophthisis, autosomal recessive osteopetrosis, peroxisome biogenesis disorder, congenital non-bullous ichthyosiform erythroderma, Seckel syndrome, Usher syndrome, autosomal recessive cutis laxa type 1, autosomal recessive cutis laxa type 2, hearing loss, autosomal recessive, microcephaly, growth restriction, and increased sister chromatid exchange 2, encephalopathy, progressive, early-onset, with brain edema and/or leukoencephalopathy, 1, congenital vertebral-cardiac-renal anomalies syndrome, hair defect with photosensitivity and intellectual disability syndrome, autosomal recessive severe congenital neutropenia, severe combined immunodeficiency due to CARMIL2 deficiency, extraoral halitosis due to methanethiol oxidase deficiency, neurodevelopmental disorder with microcephaly, impaired language, epilepsy, and gait abnormalities, mitochondrial complex 2 deficiency, nuclear type 3, mismatch repair cancer syndrome, spondyloepimetaphyseal dysplasia with joint laxity, type 3, Kilquist syndrome, Duane anomaly-myopathy-scoliosis syndrome, autosomal recessive axonal charcot-marie-tooth disease due to copper metabolism defect, immune dysregulation-inflammatory bowel disease-arthritis-recurrent infections-lymphopenia syndrome, optic atrophy-ataxia-peripheral neuropathy-global developmental delay syndrome, congenital myopathy with reduced type 2 muscle fibers, NAD(P)HX dehydratase deficiency, autosomal recessive ocular albinism, ichthyosis linearis circumflexa, eosinophil peroxidase deficiency, hyperphenylalaninemia due to DNAJC12 deficiency, autosomal recessive epidermolytic ichthyosis, Ehlers-Danlos syndrome, classic-like, 2, joint laxity, short stature, and myopia, HELIX syndrome, auditory neuropathy-optic atrophy syndrome, glycosylphosphatidylinositol biosynthesis defect 15, neurodegeneration, childhood-onset, stress-induced, with variable ataxia and seizures, SCN4A-related myopathy, autosomal recessive, Uner Tan Syndrome, nephropathic cystinosis, Imerslund-Grasbeck syndrome type 1, Imerslund-Grasbeck syndrome type 2, permanent neonatal diabetes mellitus 1, growth hormone insensitivity with immune dysregulation 1, autosomal recessive, Rajab interstitial lung disease with brain calcifications 1, Roberts-SC phocomelia syndrome, neurodevelopmental disorder with microcephaly, impaired language, and gait abnormalities, RPE65-related recessive retinopathy, GUCY2D-related recessive retinopathy, autosomal recessive titinopathy, intellectual disability, autosomal recessive, ALPL-related autosomal recessive hypophosphatasia, spastic paraplegia 18b, autosomal recessive, CEP164-related ciliopathy, RP1-related recessive retinopathy, pseudohypoaldosteronism, type IB2, autosomal recessive, pseudohypoaldosteronism, type IB3, autosomal recessive, spastic paraplegia 30B, autosomal recessive, cerebral arteriopathy, autosomal recessive, with subcortical infarcts and leukoencephalopathy 1, brain small vessel disease 2B, autosomal recessive, IMPG1-related recessive retinopathy, PROM1-related recessive retinopathy

Genetics & variants

GWAS landscape

No GWAS associations recorded — common-variant (GWAS) studies don’t cover this disease (typical for Mendelian / rare diseases). See the curated gene cohort and Mendelian overlap below.

Variant details and genetic-evidence tiers

ClinVar germline variants

50 retrieved; paginated sample, class counts are floors:

17 uncertain significance, 11 pathogenic/likely pathogenic, 9 conflicting classifications of pathogenicity, 8 benign/likely benign, 2 pathogenic, 2 benign, 1 likely pathogenic

ClinVar	Variant (HGVS)	Gene	Classification	Review
12781	NM_003000.3(SDHB):c.725G>A (p.Arg242His)	SDHB	Pathogenic/Likely pathogenic	criteria provided, multiple submitters, no conflicts
142637	NM_003000.3(SDHB):c.689G>A (p.Arg230His)	SDHB	Pathogenic/Likely pathogenic	criteria provided, multiple submitters, no conflicts
183735	NM_003000.3(SDHB):c.649C>T (p.Arg217Cys)	SDHB	Pathogenic/Likely pathogenic	criteria provided, multiple submitters, no conflicts
183747	NM_003000.3(SDHB):c.600G>T (p.Trp200Cys)	SDHB	Pathogenic/Likely pathogenic	criteria provided, multiple submitters, no conflicts
183793	NM_003000.3(SDHB):c.137G>A (p.Arg46Gln)	SDHB	Pathogenic/Likely pathogenic	criteria provided, multiple submitters, no conflicts
183814	NM_003000.3(SDHB):c.380T>G (p.Ile127Ser)	SDHB	Pathogenic/Likely pathogenic	criteria provided, multiple submitters, no conflicts
183925	NM_003000.3(SDHB):c.541-2A>G	SDHB	Pathogenic/Likely pathogenic	criteria provided, multiple submitters, no conflicts
18454	NM_003000.3(SDHB):c.418G>T (p.Val140Phe)	SDHB	Pathogenic/Likely pathogenic	criteria provided, multiple submitters, no conflicts
185342	NM_003000.3(SDHB):c.166_170del (p.Pro56fs)	SDHB	Pathogenic	criteria provided, multiple submitters, no conflicts
186150	NM_003000.3(SDHB):c.574T>C (p.Cys192Arg)	SDHB	Pathogenic	criteria provided, multiple submitters, no conflicts
1916161	NM_003000.3(SDHB):c.637dup (p.Met213fs)	SDHB	Pathogenic/Likely pathogenic	criteria provided, multiple submitters, no conflicts
3892375	NM_003000.3(SDHB):c.718_719del (p.Leu240fs)	SDHB	Pathogenic/Likely pathogenic	criteria provided, multiple submitters, no conflicts
428931	NM_003000.3(SDHB):c.424-1G>A	SDHB	Pathogenic/Likely pathogenic	criteria provided, multiple submitters, no conflicts
845283	NM_003000.3(SDHB):c.589C>T (p.Pro197Ser)	SDHB	Likely pathogenic	criteria provided, multiple submitters, no conflicts
1493254	NM_003000.3(SDHB):c.269G>T (p.Arg90Leu)	SDHB	Conflicting classifications of pathogenicity	criteria provided, conflicting classifications
239420	NM_003000.3(SDHB):c.113G>A (p.Arg38His)	SDHB	Conflicting classifications of pathogenicity	criteria provided, conflicting classifications
371795	NM_003000.3(SDHB):c.709C>T (p.Pro237Ser)	SDHB	Conflicting classifications of pathogenicity	criteria provided, conflicting classifications
3892373	NM_003000.3(SDHB):c.281G>A (p.Arg94Lys)	SDHB	Conflicting classifications of pathogenicity	criteria provided, conflicting classifications
39584	NM_003000.3(SDHB):c.143A>T (p.Asp48Val)	SDHB	Conflicting classifications of pathogenicity	criteria provided, conflicting classifications
412466	NM_003000.3(SDHB):c.440A>G (p.Tyr147Cys)	SDHB	Conflicting classifications of pathogenicity	criteria provided, conflicting classifications
412492	NM_003000.3(SDHB):c.455C>T (p.Ser152Phe)	SDHB	Conflicting classifications of pathogenicity	criteria provided, conflicting classifications
584582	NM_003000.3(SDHB):c.769C>G (p.Leu257Val)	SDHB	Conflicting classifications of pathogenicity	criteria provided, conflicting classifications
658058	NM_003000.3(SDHB):c.46A>G (p.Thr16Ala)	SDHB	Conflicting classifications of pathogenicity	criteria provided, conflicting classifications
459163	NM_003000.3(SDHB):c.65G>T (p.Cys22Phe)	LOC129929542	Uncertain significance	criteria provided, multiple submitters, no conflicts
1433386	NM_003000.3(SDHB):c.343C>G (p.Arg115Gly)	SDHB	Uncertain significance	criteria provided, multiple submitters, no conflicts
1472079	NM_003000.3(SDHB):c.73G>T (p.Ala25Ser)	SDHB	Uncertain significance	criteria provided, multiple submitters, no conflicts
185456	NM_003000.3(SDHB):c.193C>T (p.Leu65Phe)	SDHB	Uncertain significance	criteria provided, multiple submitters, no conflicts
371792	NM_003000.3(SDHB):c.749C>T (p.Thr250Ile)	SDHB	Uncertain significance	criteria provided, multiple submitters, no conflicts
3763232	NM_003000.3(SDHB):c.682G>A (p.Glu228Lys)	SDHB	Uncertain significance	criteria provided, multiple submitters, no conflicts
412452	NM_003000.3(SDHB):c.395A>G (p.His132Arg)	SDHB	Uncertain significance	criteria provided, multiple submitters, no conflicts

Genes & proteins

Mendelian disease overlap and somatic drivers

GenCC: 16 · Orphanet: 7 · OMIM-shared: 0 · Dual-evidence (GWAS+Mendelian): 0

GenCC gene–disease validity (cohort genes)

the Disease column is the GenCC-asserted condition — a cohort gene’s strongest validity may be for a related predisposition syndrome.

Gene	Classification	Inheritance	Disease	Records
SDHB	Strong	Autosomal recessive	mitochondrial complex 2 deficiency, nuclear type 4	16

Orphanet rare-disease linkage (cohort genes)

Gene	Orphanet ID	Rare disease
SDHB	Orphanet:139411	Carney triad
SDHB	Orphanet:201	Cowden syndrome
SDHB	Orphanet:276621	Sporadic pheochromocytoma/secreting paraganglioma
SDHB	Orphanet:29072	Hereditary pheochromocytoma-paraganglioma
SDHB	Orphanet:3208	Isolated succinate-CoQ reductase deficiency
SDHB	Orphanet:44890	Gastrointestinal stromal tumor
SDHB	Orphanet:97286	Carney-Stratakis syndrome

Cohort genes → proteins

1 cohort genes, 1 distinct canonical proteins.

Evidence partition

Subset	Genes
multi_evidence	1

Cohort genes (full)

Symbol	HGNC	Ensembl	UniProt	Name	Evidence
SDHB	HGNC:10681	ENSG00000117118	P21912	Succinate dehydrogenase [ubiquinone] iron-sulfur subunit, mitochondrial	gencc,clinvar

Cohort function summary

Lead sentence per gene, UniProt-curated.

Symbol	Protein name	Function (lead sentence)
SDHB	Succinate dehydrogenase [ubiquinone] iron-sulfur subunit, mitochondrial	Iron-sulfur protein (IP) subunit of the succinate dehydrogenase complex (mitochondrial respiratory chain complex II), responsible for transferring electrons from succinate to ubiquinone (coenzyme Q).

Protein-family classification

Druggable: 1 · Difficult: 0 · Unknown: 0 · Druggable fraction: 1.0

Family distribution

Cohort families vs a genome-wide background (hypergeometric, BH-FDR; fold = observed/expected). Counts kept; sorted by enrichment, so the catch-all Other/Unknown bucket no longer leads.

Family	Genes	Fold	FDR
Enzyme (other)	1	12.0×	0.083

Per-gene assignment

Symbol	Family	Druggable?	EC	InterPro (top 3)
SDHB	Enzyme (other)	yes	1.3.5.1	2Fe-2S_ferredoxin-type, Succ_DH/fum_Rdtase_Fe-S, 2Fe2S_fd_BS

Expression context

Cohort genes with no expression data: 0.

1 cohort gene are a single-cell marker in ≥1 SCXA experiment.

Breadth distribution (Bgee present_calls)

Bucket	Genes
narrow (1-5 tissues)	0
moderate (6-20)	0
broad (>20)	1
unknown	0

Top tissues across cohort

Tissue	Cohort genes
apex of heart	1
cardiac ventricle	1
heart left ventricle	1

Per-gene tissue summary (top 30)

Symbol	Bgee breadth	FANTOM5 breadth	SCXA	Top tissues
SDHB	293	ubiquitous	marker	heart left ventricle, cardiac ventricle, apex of heart

Protein interactions among cohort

Intra-cohort edges: 0.

Hub genes (top 10 by interactor count)

Symbol	Interactor count
SDHB	5,471

Structural data

PDB: 1 · AlphaFold-only: 0 · No structure: 0

Cohort genes with PDB structures (top 30)

Symbol	UniProt	PDB entries
SDHB	P21912	6

Function

Pathway analysis

Distinct Reactome pathways touched by cohort: 5. Enrichment computed across 1 evidence-associated genes (1 with Reactome annotation).

Pathways by enrichment

Over-representation of cohort genes vs the genome-wide background (hypergeometric test, Benjamini-Hochberg FDR; fold = observed/expected over 1 annotated cohort genes). Counts and members are kept as ground-truth; sorted by enrichment.

Pathway	Cohort genes	Fold	FDR	Sample cohort genes
Maturation of TCA enzymes and regulation of TCA cycle	1	571.0×	0.006	SDHB
Citric acid cycle (TCA cycle)	1	423.0×	0.006	SDHB
Respiratory electron transport	1	95.2×	0.014	SDHB
Aerobic respiration and respiratory electron transport	1	88.5×	0.014	SDHB
Metabolism	1	11.6×	0.086	SDHB

GO biological processes by enrichment

Over-representation of cohort genes vs the genome-wide background (hypergeometric test, Benjamini-Hochberg FDR; fold = observed/expected over 1 annotated cohort genes). Counts and members are kept as ground-truth; sorted by enrichment.

GO term	Cohort genes	Fold	FDR	Sample cohort genes
succinate metabolic process	1	3370.4×	9e-04	SDHB
mitochondrial electron transport, succinate to ubiquinone	1	3370.4×	9e-04	SDHB
respiratory electron transport chain	1	842.6×	0.002	SDHB
tricarboxylic acid cycle	1	510.7×	0.003	SDHB
proton motive force-driven mitochondrial ATP synthesis	1	263.3×	0.004	SDHB
aerobic respiration	1	247.8×	0.004	SDHB

Therapeutics

Drug target analysis

Approved (phase 4): 0 · Phase ≥3: 0 · Phased (≥1): 0 · Undrugged: 1

Druggability breadth: 1 of 1 evidence-associated genes (100%) have a ChEMBL target (buckets above are over the deeply-mined display cohort).

Top cohort targets by molecule count

Symbol	Molecules	Max phase
SDHB	0	0

Bioactivity and enzyme data

Enzyme cohort genes (≥1 EC): 1.

Cohort genes with ChEMBL bioactivity (full, sorted by assay count)

Symbol	Assays	Type breakdown
SDHB	4	Binding:4

Cohort enzymes (BRENDA EC)

Symbol	EC numbers	Names
SDHB	1.3.5.1	succinate dehydrogenase

Pharmacogenomics

Cohort genes with a PharmGKB record: 1; with CPIC/DPWG dosing guidelines: 0.

No cohort gene has a CPIC/DPWG genotype-guided dosing guideline (PharmGKB).

Chemical tractability of cohort targets

0 approved/phased compounds have measured bioactivity against a cohort gene (and aren’t yet in disease-level trials). This is a research / tractability signal, NOT a therapeutic recommendation — a bioactivity row often reflects off-target or screening binding (e.g. promiscuous kinase inhibitors against a cohort kinase), implying no disease mechanism.

Druggability pyramid

Cohort genes binned by druggability tier (high → low):

Tier	Definition	Genes	Symbols
A	Approved (phase 4 drug)	0
B	Phased (≥1) drug, not yet approved	0
C	Druggable family + PDB, no drug	1	SDHB
D	Druggable family + AlphaFold only, no drug	0
E	Difficult family or no structure, no drug	0

Undrugged target profiles

1 cohort genes are undrugged. Ranked by ‘starting-point quality’ (assay depth + drugged-partner adjacency).

Symbol	ChEMBL assays	Drugged partners (top 3)
SDHB	4	—

Clinical trials & evidence

Clinical trials

Clinical trials: 0.