Maple syrup urine disease

General Information (adopted from Orphanet):

Synonyms, Signs: MSUD
Leucinosis
BCKD deficiency
BCKDH deficiency
Branched-chain ketoaciduria
Branched-chain ketoacid dehydrogenase deficiency
Number of Symptoms 33
OrphanetNr: 511
OMIM Id: 248600
615135
ICD-10: E71.0
UMLs: C0024776
C0268576
MeSH: D008375
MedDRA: 10026817
Snomed: 190700007
24013007
27718001

Prevalence, inheritance and age of onset:

Prevalence: < 1 of 100 000 [Orphanet]
Inheritance: Autosomal recessive
[Orphanet]
Age of onset: Antenatal
Neonatal
Infancy
Childhood
[Orphanet]

Disease classification (adopted from Orphanet):

Parent Diseases: Disorder of branched-chain amino acid metabolism
 -Rare genetic disease

Comment:

MSUD is due to mutations in genes encoding the first 3 subunits of branched chain 2-ketoacid dehydrogenase (BCKAD). The genes are BCKDHA (19q13.1-q13.2), encoding E1a, BCKDHB (6q14.1), encoding E1b, and DBT (1p31), encoding E2 respectively. Mutations lead to accumulation of branched-chain amino acids (especially leucine) and branched-chain alpha-ketoacids. In classic MSUD, mutations in BCKDHA predominate [Orphanet].

Symptom Information: Sort by abundance 

1
(HPO:0003355) Aminoaciduria Very frequent [Orphanet] 65 / 7739
2
(HPO:0000600) Abnormality of the pharynx Very frequent [Orphanet] 22 / 7739
3
(HPO:0002321) Vertigo Frequent [Orphanet] 58 / 7739
4
(HPO:0002141) Gait imbalance Frequent [Orphanet] 55 / 7739
5
(HPO:0001251) Ataxia Frequent [Orphanet] typical [HPO] 413 / 7739
6
(HPO:0002133) Status epilepticus Very frequent [Orphanet] 59 / 7739
7
(HPO:0002311) Incoordination Frequent [Orphanet] 84 / 7739
8
(HPO:0004374) Hemiplegia/hemiparesis Frequent [Orphanet] 158 / 7739
9
(HPO:0008376) Nasal, dysarthic speech Very frequent [Orphanet] 8 / 7739
10
(HPO:0002301) Hemiplegia Frequent [Orphanet] typical [HPO] 42 / 7739
11
(HPO:0001269) Hemiparesis Frequent [Orphanet] typical [HPO] 51 / 7739
12
(HPO:0001265) Hyporeflexia Very frequent [Orphanet] hallmark [HPO] 208 / 7739
13
(HPO:0011097) Epileptic spasms Very frequent [Orphanet] 45 / 7739
14
(HPO:0001328) Specific learning disability Very frequent [Orphanet] 114 / 7739
15
(HPO:0001250) Seizures Very frequent [Orphanet] 1245 / 7739
16
(HPO:0002121) Absence seizures Very frequent [Orphanet] 62 / 7739
17
(HPO:0001270) Motor delay Very frequent [Orphanet] 322 / 7739
18
(HPO:0001263) Global developmental delay Very frequent [Orphanet] 853 / 7739
19
(HPO:0001284) Areflexia Very frequent [Orphanet] hallmark [HPO] 198 / 7739
20
(HPO:0002066) Gait ataxia Frequent [Orphanet] typical [HPO] 327 / 7739
21
(HPO:0100543) Cognitive impairment Very frequent [Orphanet] 230 / 7739
22
(HPO:0001249) Intellectual disability Very frequent [Orphanet] 1089 / 7739
23
(HPO:0001315) Reduced tendon reflexes Very frequent [Orphanet] 160 / 7739
24
(HPO:0011147) Typical absence seizures Very frequent [Orphanet] 33 / 7739
25
(HPO:0004337) Abnormality of amino acid metabolism Very frequent [Orphanet] 45 / 7739
26
(HPO:0002098) Respiratory distress Very frequent [Orphanet] 75 / 7739
27
(HPO:0002094) Dyspnea Very frequent [Orphanet] 132 / 7739
28
(HPO:0001608) Abnormality of the voice Very frequent [Orphanet] 126 / 7739
29
(HPO:0001611) Nasal speech Very frequent [Orphanet] 48 / 7739
30
(HPO:0100271) Hyponasal speech Very frequent [Orphanet] 7 / 7739
31
(HPO:0002093) Respiratory insufficiency Very frequent [Orphanet] 410 / 7739
32
(HPO:0001252) Muscular hypotonia Very frequent [Orphanet] 990 / 7739
33
(HPO:0001324) Muscle weakness Very frequent [Orphanet] hallmark [HPO] 859 / 7739

Associated genes:

ClinVar (via SNiPA)

Gene symbol Variation Clinical significance Reference

Additional Information:

Diagnosis GeneReviews Manifestations of classic maple syrup urine disease (MSUD) in untreated neonates include:...
Clinical Description GeneReviews Traditionally, the metabolic phenotype of MSUD is termed classic or intermediate on the basis of residual BCKAD enzyme activity. Rarely, affected individuals have partial BCKAD enzyme deficiency that only manifests intermittently or responds to dietary thiamine therapy (Table 2). Phenotypic distinctions are not absolute: individuals with intermediate or intermittent forms of MSUD can experience severe metabolic intoxication and encephalopathy if physiologic stress is sufficient to overwhelm residual BCKAD activity or this activity is reduced by transient changes in the phosphorylation state of the enzyme complex. Even in persons with relatively high baseline residual BCKAD enzyme activity, episodes of metabolic intoxication can be fatal [Chuang & Shih 2001]....
Genotype-Phenotype Correlations GeneReviews The severity of the MSUD metabolic phenotype is determined by the amount of residual BCKAD enzyme activity relative to dietary BCAA excess and the large demands for BCAA oxidation that accompany fasting, illness, or other catabolic stresses [Felig et al 1969, Morton et al 2002, Strauss & Morton 2003, Strauss et al 2010]. The distinction between classic and intermediate MSUD provides an example. For individuals with borderline enzyme activity (e.g., 3%-10%), disease expression is influenced by a large number of variables in addition to genotype, including the rate of growth (and net protein synthesis), calorie intake, the quality and quantity of dietary protein, the frequency and severity of precipitating illnesses, and the developmental timing of metabolic disturbances. ...
Differential Diagnosis GeneReviews Entities to exclude in the encephalopathic neonate include birth asphyxia, hypoglycemia, status epilepticus, kernicterus, meningitis, and encephalitis. The few inborn errors of metabolism that present with neonatal encephalopathy include:...
Management GeneReviews Establishing the extent of disease in an individual diagnosed with maple syrup urine disease (MSUD). To determine whether an individual has either classic or intermediate MSUD, it is useful to focus on concentration ratios among the BCAAs and between leucine and other essential and non-essential amino acids. Regulated concentration ratios among the full complement of circulating amino acids are one indication of in vivo residual BCKAD enzyme activity. These ratios are normally maintained within a narrow range by balanced transport of branched-chain and other essential amino acids across common carriers (LAT1/2), intracellular transamination equilibria, and coordinated activity of multiple catabolic pathways [Boado et al 1999, Matsuo et al 2000, Killian & Chikhale 2001, Umeki et al 2002, Brosnan 2003]....
Molecular genetics GeneReviews Information in the Molecular Genetics and OMIM tables may differ from that elsewhere in the GeneReview: tables may contain more recent information. —ED....