Maple Syrup Urine Disease 2012
Contents
Summary
Maple Syrup Urine Disease is an autosomal recessive disorder, which affects the degradation of the branched amino acids Leu, Ile, Val. The name comes from a maple syrup odor of affected patients urine, with is caused by high levels of sotolon [1] in the patient's urine.
Phenotype
Symptoms shown almost immediately after birth include poor feeding, vomiting, dehydration, lethargy, hypotonia, seizures, hypoglycaemia, ketoacidosis, opisthotonus, pancreatitis, coma and neurological decline [2]. Within a week after birth the neurological damage is irreversible. The most prominent symptom is probably the sweet smelling urine, that is often characterized as maple syrup like, hence the name. In Mediterranean or eastern countries, where maple syrup is rather uncommon, it is reminiscent as fenugreek[3].
MSUD is classified in four categories, according to the amount and type of remaining enzyme activity[4]:
- Classic severe MSUD. The most common variant. Remaining enzymatic activity below 2%. Symptoms usually show within the first few days of life. Severely restricted diet necessary.
- Intermediate MSUD. Remaining enzymatic activity usually between 3-8%. Somewhat better branched chain amino acid tolerance, when healthy. During illness tolerance is usually reduced. Treatment similar to classic MSUD.
- Intermittent MSUD. Remaining enzymatic activity usually between 8-15%. Symptoms only show during episodes (mostly caused by illness or huge protein intake).
- Thiamine-responsive MSUD. Medication with large amounts of Thiamine restores enzymatic function. Only moderate diet necessary. Unfortunately not very common variant.
Biochemical disease mechanism
MSUD affects a protein called branched-chain alpha-keto acid dehydrogenase complex (BCKDHC), which is involved in the degradation of branched amino acids (Val, Leu, Ile). The inability of degrading these amino acids, leads to an enrichment of those in the body. The elevated levels of amino acids in the urine generate the smell, which is reminiscent of maple syrup. BCKDHC consists of four subunits:
| subunit | name | chromosomal gene location | MSUD-type |
|---|---|---|---|
| BCKDHA | Branched chain keto acid dehydrogenase E1, alpha polypeptide | 19q13.1-q13.2 | 1a |
| BCKDHB | branched chain keto acid dehydrogenase E1, beta polypeptide | 6q14.1 | 1b |
| DBT | Dihydrolipoamide branched chain transacylase E2 | 1p31 | 1/2 |
| DLD | dihydrolipoamide dehydrogenase | 7q31-q32 | 3 |
Mutations
Reference sequence
Mutated sequence
- Nonsense/missense mutated sequence BCKDHA
>sp|P12694|ODBA_HUMAN 2-oxoisovalerate dehydrogenase subunit alpha, mitochondrial OS=Homo sapiens GN=BCKDHA PE=1 SV=2 MAVAIAAARVWRLNRGLSQAALLLLRQPGARGLARSHPPRQQQQFSSLDDKPQFPGASAE FIDKLEFIQPNVISGIPIYRVMDRQGQIINPSEDPHLPKEKVLKLYKSMTLLNTMDRILY ESQRQGRISFYMTNYGEEGTHVGSAAALDNMNLVFGQYWEAGVLMNQDYPLELFMAQCYG NISDLGKGRKMPVHYGCKERHFVTISSPLATQTPQVVGAAYAAKRANANRVVICYFGEGA ASEGDAHASFNFTATLEYPIIFFWWNSGYAISTPTSEQYRGDDIPA|GPRYGIMSIC/HVD SNAVFAVYNARKEA|RRAVAENQPFLTKTMTYRIGHHSTSDDSSAYHSVDEVNYWDKQDH PISWLRHYLLSQGWWDEEQEKAWRKQSRRKVMEAFEQAERKPKPNPNLLCSDMH/CQEMPA QLRKQQESLARHLQTYGEHNPLDHFDK
- Nonsense/missense mutated sequence BCKDHB
>sp|P21953|ODBB_HUMAN 2-oxoisovalerate dehydrogenase subunit beta, mitochondrial OS=Homo sapiens GN=BCKDHB PE=1 SV=2 MAVVAAAAGWLLRLRAAGAEGHWRRLPGAGLARGFLHPAATVEDAAQRRQVAHFTFQPDP EPREYGQTQKMNLFQSVTSALDNSLAKDPTAVIFGEDVAFGGVFRCTVGL|DKYGKDRGF NTLLCEQGIGGFGIRIVVTGATAIAEIQFADYIFPAFDKIVN|AAKYH/CYRSWDLFYCGS LTIPSPWGCDGHGALYHSQSAEAFFAR/YCPGIKVVKPGSPFQARGLLLSCIEDKNPCIFF EP|ILHRAAAEEAPIEPYNIPLSQAEVI|EGSDVTLVACSTQVHAI|EVASMAKEKLGVS CEVIDLRTIIPWDVDTICKSVIKTG|LLISHEAPLTGGFALKISSTVQEECFLNLEALIS RVCGYDTPFPHIF|PFYIPDKWKC|DALRKMINY
- Nonsense/missense mutated sequence DBT (leading to type 1)
>sp|P11182|ODB2_HUMAN Lipoamide acyltransferase component of branched-chain alpha-keto acid dehydrogenase complex, mitochondrial OS=Homo sapiens GN=DBT PE=1 SV=3 MAAVRMLRTWSRNAGKLICVRYFQTCGNVHVLKPNYVCFFGYPSFKYSHPHHFLKTTAAL RGQVVQFKLSDIGEGIREVTVKEWYVKEGDTVSQFDSMCEVQSDKASVTITSRYDGVIKK LYYNLDDIAYVRKPLVDTETEALKDSEEDVVETPAVSHDEHTHQEIKGRKTLATPAVRRL AMENNIKLSEVVG|GKDGRILKEDILNYLEKQTGAILPPSPKV|IMPPPPKPKDMTVPIL VSKPPVFTGKDKTEPIKGFQKATVKTMSAALKIPHCGYCDEIDLTELVKLREELKPIAFA RGIKLSSMPFFLNAASLGLLQFPILNASVDENCQNITYKASNNIGIAMDTEQGLIVPNVK NVQICSIFDIATELNRLQKLGSVSQLSTTGLTGGTFTPSNIGSIGGTFAKQVIMPPEVAI GALGSIKANPRFNQKGEVYKAQIMNMSWSDDRRVIDGATMSPFSNLWKSYLENPAFMLLD LK
- Nonsense/missense mutated sequence DBT (leading to type 2)
>sp|P11182|ODB2_HUMAN Lipoamide acyltransferase component of branched-chain alpha-keto acid dehydrogenase complex, mitochondrial OS=Homo sapiens GN=DBT PE=1 SV=3 MAAVRMLRTWSRNAGKLICVRYFQTCGNVHVLKPNYVCFFGYPSFKYSHPHHFLKTTAAL RGQVVQFKLSDIGEGIREVTVKEWYVKEGDTVSQFDSMCEVQSDKASVTITSRYDGVIKK LYYNLDDIAYVRKPLVDTETEALKDSEEDVVETPAVSHDEHTHQEIKGRKTLATPAVRRL AMENNIKLSEVVG|GKDGRILKEDILNYLEKQTGAILPPSPKV|IMPPPPKPKDMTVPIL VSKPPVFTGKDKTEPIKGFQKATVKTMSAALKIPHCGYCDEIDLTELVKLREELKPIAFA RGIKLSSMPFFLNAASLGLLQFPILNASVDENCQNITYKASNNIGIAMDTEQGLIVPNVK NVQICSIFDIATELNRLQKLGSVSQLSTTGLTGGTFTPSNIGSIGGTFAKQVIMPPEVAI GALGSIKANPRFNQKGEVYKAQIMNMSWSDDRRVIDGATMSPFSNLWKSYLENPAFMLLD LK
- Nonsense/missense mutated sequence DLD
>sp|P09622|DLDH_HUMAN Dihydrolipoyl dehydrogenase, mitochondrial OS=Homo sapiens GN=DLD PE=1 SV=2 MQSWSRVYCSLAKRGHFNRISHGLQGLSAVPLRTYADQPIDADVTVIGSGPGGYVAAIKA AQLGFKTVCIEENETLGGTCLNVGCIPSKALLNNSHYYHMAHGTDFASRGIEMSEVRLNL DKMMEQKSTAVKALTGGIAHLFKQNKVVHVNGYGKITGKNQVTATKADGGTQVIDTKNIL IATGSEVTPFPGITIDEDTIVSSTGALSLKKVPEKMVVIGAGVIGVELCSVWQRLGADVT AVEFLGHVGGVGIDMEISKNFQRILQKQGFKFKLNTKVTGATKKSDGKIDVSIEAASGGK AEVITCDVLLVCIGRRPFTKNLGLEELGIEVDPRGRIPVNTRFQTKIPNIYAIGDVVAGP MLAHKAEDEGIICVEGMAGGAVHIDYNCVPSVIYTHPEVAWVGKSEEQLKEEGIEYKVGK FPFAANSRAKTNADTDGMVKILGQKSTDRVLGAHILGPGAGEMVNEAALALEYGASCEDI ARVCHAHLTLSEAFGEANLAASFGKSINF
