Download Maple Syrup Urine Disease

Maple Syrup Urine Disease (MSUD)
By Jenny Morrison (836445)
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Deficiency in branched chain
alpha-keto acid
dehydrogenase complex
(BCKAD) – located in
mitochondrial inner membrane
Caused by mutation in 4
possible genes BCKDHA,
BCKDHB, DBT, and DLD that
encode for the BCKAD
Results in defect in
metabolism of branched chain
amino acids (BCAA): Valine,
Leucine and Isoleucine
Accumulation of BCAA and
their keto acid derivatives
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5 clinical subtypes: “classic”
“intermittent”, “mild”, Thiamine
responsive, and E3-deficient
with lactic acidosis.
Classification of subtypes
according to nature of gene
mutation by genetic
complementation analysis after
somatic cell hybridisation
(1980)
Classic MSUD is the most
severe and most common form
Symptoms –
“classic” MSUD
4 of the MSUD
clinical subtypes
Onset in the first week of life:
 Maple syrup odour (in urine
and on body)
 Feeding difficulties and
vomiting
 Shrill cry
 Hypertonicity (episodes
alternate with flaccidity)
 No Moro reflex and
suppressed deep tendon
reflexes
 Frequent convulsions
 Survivors suffer from severe
mental retardation & motor
development retardation
(Bondy & Rosenberg, 1980)
Inheritance
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Autosomal recessive
Frequency:
 1 in 185,000 newborns world wide (Chuang et al, 1995)
 1 in 176 newborns in the Mennonite population of Lancaster,
Pennsylvania (due to consanguinity)
Panethnic distribution
Genetic Counselling
 Relatives of the affected individual have high genetic risks (1 in 4)
 Extremely low risks to offsprings of healthy sibs or more distant
relatives
Molecular genetics of the BCKAD
Molecular
Phenotypes
Genes
Chromosome
Exons
T’script
length
T’slation
Length
IA
E1α
19q13.1 – 13.2
9
1352
445
6p21 – p22
10
1179
392
1p31
11
2384
482
7q31 - 32
14
2320
509
BCKDHA
IB
E1β
BCKDHB
II
E2
DBT
III
E3
DLD
 each molecular phenotype can have > 1 clinical phenotype as different
mutations in the same subunit may have different effects on the stability and
function of the polypeptide.
 MSUD type II constitute the majority of mutations reported
MSUD Type IA
E1α
mRNA sequence
1 gccggaccgc tgagtggttg ttagccaaga tggcggtagc gatcgctgca gcgagggtct
1561cagcagttgc tgaggctccg tcagccccct cttcacctgt tgttacagtg ccttctccca
61 ggcggctaaa ccgtggtttg agccaggctg ccctcctgct gctgcggcag cctggggctc
1621ggggctgggt gagggcacat tcaggactag aagcccctct gggcatgggg tggacatggc
121 ggggactggc tagatctcac ccccccaggc agcagcagca gttttcatct ctggatgaca
1681aggtcagcct gtggaacttg cgcaggtgcg agtggccagc agaggtcacg aataaactgc
181 agccccagtt cccaggggcc tcggcggagt ttatagataa gttggaattc atccagccca
1741atctctgcgc ctggctctct accaaaaaaa aaaaaaaaaa a
241 acgtcatctc tggaatcccc atctaccgcg tcatggaccg gcaaggccag atcatcaacc
301 ccagcgagga cccccacctg ccgaaggaga aggtgctgaa gctctacaag agcatgacac
361tgcttaacac catggaccgc atcctctatg agtctcagcg gcagggccgg atctccttct
421acatgaccaa ctatggtgag gagggcacgc acgtggggag tgccgccgcc ctggacaaca
481 cggacctggt gtttggccag taccgggagg caggtgtgct gatgtatcgg gactaccccc
541tggaactatt catggcccag tgctatggca acatcagtga cttgggcaag gggcgccaga
601tgcctgtcca ctacggctgc aaggaacgcc acttcgtcac tatctcctct ccactggcca
661cgcagatccc tcaggcggtg ggggcggcgt acgcagccaa gcgggccaat gccaacaggg
721tcgtcatctg ttacttcggc gagggggcag ccagtgaggg ggacgcccat gccggcttca
781acttcgctgc cacacttgag tgccccatca tcttcttctg ccggaacaat ggctacgcca
841tctccacgcc cacctctgag cagtatcgcg gcgatggcat tgcagcacga ggccccgggt
901atggcatcat gtcaatccgc gtggatggta atgatgtgtt tgccgtatac aacgccacaa
Protein Sequence
MAVAIAAARVWRLNRGLSQAALLLLRQPGARGLARSH
PPRQQQQFSSLDDKPQFPGASAEFIDKLEFIQPNVISGI
PIYRVMDRQGQIINPSEDPHLPKEKVLKLYKSMTLLNT
MDRILYESQRQGRISFYMTNYGEEGTHVGSAAALDNT
DLVFGQYREAGVLMYRDYPLELFMAQCYGNISDLGKG
RQMPVHYGCKERHFVTISSPLATQIPQAVGAAYAAKRA
NANRVVICYFGEGAASEGDAHAGFNFAATLECPIIFFCR
NNGYAISTPTSEQYRGDGIAARGPGYGIMSIRVDGNDV
FAVYNATKEARRRAVAENQPFLIEAMTYRIGHHSTSDD
SSAYRSVDEVNYWDKQDHPISRLRHYLLSQGWWDEE
QEKAWRKQSRRKVMEAFEQAERKPKPNPNLLFSDVY
QEMPAQLRKQQESLARHLQTYGEHYPLDHFDK
961aggaggcccg acggcgggct gtggcagaga accagccctt cctcatcgag gccatgacct
1021acaggatcgg gcaccacagc accagtgacg acagttcagc gtaccgctcg gtggatgagg
1081tcaattactg ggataaacag gaccacccca tctcccggct gcggcactat ctgctgagcc
Exon
Codon
Mutation
Consequence
9
393
TAC → AAC
Tyr → Asn
7
242
8-bp deletion
Frameshift
9
368
TAT → TGT
Tyr → Cys
2
4
CAG → CCAG
Frameshift
6
222
AAT → AGT
Asn → Ser
1141aaggctggtg ggatgaggag caggagaagg cctggaggaa gcagtcccgc aggaaggtga
1201tggaggcctt tgagcaggcc gagcggaagc ccaaacccaa ccccaaccta ctcttctcag
1261acgtgtatca ggagatgccc gcccagctcc gcaagcagca ggagtctctg gcccgccacc
1321tgcagaccta cggggagcac tacccactgg atcacttcga taagtgagac ctgctcagcc
1381cacccccacc catcctcagc taccccgaga ggtagcccca ctctaagggg agcaggggga
1441cctgacagca caccactgtc ttccccagtc agctccctct aaaatactca gcggccaggg
1501cggctgccac tcttcacccc tgctcctccc ggctgttaca ttgtcagggg acagcatctg
MSUD Type IB
E1β
mRNA transcript variant 2
1 aggcggcgtg cggctgcata gcctgagaat cccggtggtg agcggggatg gcggttgtag
61 cggcggctgc cggctggcta ctcaggctca gggcggcagg ggctgagggg cactggcgtc
121 ggcttcctgg cgcggggctg gcgcggggct ttttgcaccc cgccgcgact gtcgaggatg
181 cggcccagag gcggcaggtg gctcatttta ctttccagcc agatccggag ccccgggagt
241 acgggcaaac tcagaaaatg aatcttttcc agtctgtaac aagtgccttg gataactcat
301 tggccaaaga tcctactgca gtaatatttg gtgaagatgt tgcctttggt ggagtcttta
361 gatgcactgt tggcttgcga gacaaatatg gaaaagatag agtttttaat accccattgt
421 gtgaacaagg aattgttgga tttggaatcg gaattgcggt cactggagct actgccattg
481 cggaaattca gtttgcagat tatattttcc ctgcatttga tcagattgtt aatgaagctg
541 ccaagtatcg ctatcgctct ggggatcttt ttaactgtgg aagcctcact atccggtccc
601 cttggggctg tgttggtcat ggggctctct atcattctca gagtcctgaa gcattttttg
661 cccattgccc aggaatcaag gtggttatac ccagaagccc tttccaggcc aaaggacttc
721 ttttgtcatg catagaggat aaaaatcctt gtatattttt tgaacctaaa atactttaca
781 gggcagcagc ggaagaagtc cctatagaac catacaacat cccactgtcc caggccgaag
841 tcatacagga agggagtgat gttactctag ttgcctgggg cactcaggtt catgtgatcc
901 gagaggtagc ttccatggca aaagaaaagc ttggagtgtc ttgtgaagtc attgatctga
961 ggactataat accttgggat gtggacacaa tttgtaagtc tgtgatcaaa acagggcgac
1021 tgctaatcag tcacgaggct cccttgacag gcggctttgc atcggaaatc agctctacag
1081 ttcaggagga atgtttcttg aacctagagg ctcctatatc aagagtatgt ggttatgaca
1141 caccatttcc tcacattttt gaaccattct acatcccaga caaatggaag tgttatgatg
Protein sequence
MAVVAAAAGWLLRLRAAGAEGHWRRLPGAGL
ARGFLHPAATVEDAAQRRQVAHFTFQPDPEPR
EYGQTQKMNLFQSVTSALDNSLAKDPTAVIFGE
DVAFGGVFRCTVGLRDKYGKDRVFNTPLCEQG
IVGFGIGIAVTGATAIAEIQFADYIFPAFDQIVNEA
AKYRYRSGDLFNCGSLTIRSPWGCVGHGALYH
SQSPEAFFAHCPGIKVVIPRSPFQAKGLLLSCIE
DKNPCIFFEPKILYRAAAEEVPIEPYNIPLSQAEV
IQEGSDVTLVAWGTQVHVIREVASMAKEKLGVS
CEVIDLRTIIPWDVDTICKSVIKTGRLLISHEAPLT
GGFASEISSTVQEECFLNLEAPISRVCGYDTPF
PHIFEPFYIPDKWKCYDALRKMINY
Alternate splicing results in 2
transcripts that encode the
same protein
1201 cccttcgaaa aatgatcaac tattgaccat atagaaaagc tggaagatta tgactagata
1261 tggaaatatt ttttctgaat ttttttttat atttcctccg acttacctct ttttgaaaag
Exon
Mutation
Consequence
1
11-bp deletion
frameshift
1321 agagttttta ttaaatgaac catcatgata ttggctgaaa agttctacat tctattattg
1381 tattgtaaca cacatgtatt gatgattttc attaagagtt tcagattaac tttgaaaaat
1441 attccacatg gtaatcttat aaattctgtt taattacatc tgtaaatatt atgtgtgtga
1501 tagtattcaa taaagtaaaa tcaaattgtc aaaaaaaaaa aaaaaaaaaa aa//
MSUD Type IB cont.
mRNA transcript variant 1
1 aggcggcgtg cggctgcata gcctgagaat cccggtggtg agcggggatg gcggttgtag
61 cggcggctgc cggctggcta ctcaggctca gggcggcagg ggctgagggg cactggcgtc
121 ggcttcctgg cgcggggctg gcgcggggct ttttgcaccc cgccgcgact gtcgaggatg
181 cggcccagag gcggcaggtg gctcatttta ctttccagcc agatccggag ccccgggagt
241 acgggcaaac tcagaaaatg aatcttttcc agtctgtaac aagtgccttg gataactcat
301 tggccaaaga tcctactgca gtaatatttg gtgaagatgt tgcctttggt ggagtcttta
361 gatgcactgt tggcttgcga gacaaatatg gaaaagatag agtttttaat accccattgt
421 gtgaacaagg aattgttgga tttggaatcg gaattgcggt cactggagct actgccattg
481 cggaaattca gtttgcagat tatattttcc ctgcatttga tcagattgtt aatgaagctg
541 ccaagtatcg ctatcgctct ggggatcttt ttaactgtgg aagcctcact atccggtccc
601 cttggggctg tgttggtcat ggggctctct atcattctca gagtcctgaa gcattttttg
661 cccattgccc aggaatcaag gtggttatac ccagaagccc tttccaggcc aaaggacttc
721 ttttgtcatg catagaggat aaaaatcctt gtatattttt tgaacctaaa atactttaca
781 gggcagcagc ggaagaagtc cctatagaac catacaacat cccactgtcc caggccgaag
841 tcatacagga agggagtgat gttactctag ttgcctgggg cactcaggtt catgtgatcc
901 gagaggtagc ttccatggca aaagaaaagc ttggagtgtc ttgtgaagtc attgatctga
961 ggactataat accttgggat gtggacacaa tttgtaagtc tgtgatcaaa acagggcgac
1021 tgctaatcag tcacgaggct cccttgacag gcggctttgc atcggaaatc agctctacag
1081 ttcaggagga atgtttcttg aacctagagg ctcctatatc aagagtatgt ggttatgaca
1141 caccatttcc tcacattttt gaaccattct acatcccaga caaatggaag tgttatgatg
1201 cccttcgaaa aatgatcaac tattgaccat ataggtaggt atgcatcttg agaaagctac
1261 tatgtgcccc tgacattaac gtactgttaa ccaagacaca gcaatcatca gtgttttgat
1321 ggtaacaaac tttgatggta aagttgataa aaggcaactt tcagaagaaa ataatgtgct
1381 ttagaaaaaa aattcaaatt tatagtagta tatttacatt tttgttgttg ttgttctgag
1441 atggagtctc actctgtcgc ccaggctaga ctgcagtggt gcaatctcag ctcactgcaa
1501 cctcccccct acccccgagt tcaagcaatt ctcctgcctc agcctgctga gtagttggga
1561 ttacaggtgc ccaccaccat gcccagctaa tttttgtgtt tttattggag gtggggtttc
1621 actatgttgg ctcagctgat ttcaaattcc tgacctcaag tgatccacct gccttagcct
1681 cccaaagtgc tgggattaca ggcatgagcc actgcacctg gctatattta catttaatag
1741 aaacatatct agcatatgta tatgtgattt tttttttttt tgagaccgag tctcactctg
1801 tcaccaggct ggagtgcagt ggtgcgatct tggctcatgg caacctccgc ctcccaggtt
1861 caagcgattg tcctgcctca gtctcctgag tagctgggac tacaggtgtg caccaacatg
1921 cccagctaat tttttatatt tttagtagag acggggtttc accatgttgg ccaggatggt
1981 ctcgatctct tgaccttgtg ttccacccgt cttggcctcc caaagcgctg gaattacagg
2041 catgagccac cgcgcctggc ctgtatatgt gatttctaaa aaatagatgc atgcatatgt
2101 taacattgaa tagtcaatca ctagatgaag atgctctcta ccatggttta gattgcaagt
2161 gtactttata ccattgtttc aacttcaacc tttatttttg tatatatttt ttcaactact
2221
2281
2341
2401
2461
2521
2581
2641
2701
2761
2821
2881
2941
3001
3061
3121
3181
3241
3301
3361
3421
taaactgttc atgaataggc gtactttctg tatttaaaaa tggcccctca agcaccgtta
atttacattc cagttattta catgataatt catgacattc tgaaacttgc ctgtatatta
tctgaaaaat ggatttcttg aggaaaagat ctgtttattg tatgtaagga aaaattttac
ctgaaaacaa acaaacaaac cctaaaactc agcaccacta ccatttccag aagctttttt
agcaagtgaa tattttttac ataatggata ataaatggta tttattcatc atgattttct
aagtaatgct tatcagcccc ttcagtggtg ttattctaac aaaatgaata cattacaaat
tattaagtta gcttttcaga gttttaatat agaagttact agcactgaca cactgatttt
gaaatgtttc aaaatgagta gatacgatta gatcctttac cttttaatat ctagtttttc
caaaaatgat agtaatatct tttgaagaac tatgcttttt caaaagcaaa atcaactctg
tataatagca cattctctac tttttaaaga tcagaaatgc tagaattctt gacttttgtg
tatgggtagt aaatctagct cactgaaaat cagagtgaaa cgcctttaca tttgtgcgga
tagagaagtt aactctccct catatgtcac tgtgctacca taatccctac attttctgtc
tgttctagtc taagaatatt gttatagatg gaagttagga ccattagccc acagatgcgt
gtattctctc agacataccg gtgtagatgc catatttctg atgtcttctt aatgtctgtg
aaagcaactg gcatctacaa taaatcacac ttagaactgg ttagaggact ccctcacttt
tgttgtccat gtggttccct tccgtggacc agccgtaata aagagccaag gtagtgatgg
tggccacgtg cctcgttgct atttttaaag taatattcag atgtggtttt aaatttagat
tatgtattcc ttttgaaaca taagaaaaac atttaaacct atgctgaaaa tacgataaaa
gaaaaacaac tccaatatgc taaaagttaa atatggtatt taagaaaata gtcatgtatg
caattgagaa agtctataat ttattttaca gaaaagctgg aagattatga ctagatatgg
aaatattttt tctgaatttt tttttatatt tcctccgact tacctctttt tgaaaagaga
3481 gtttttatta aatgaaccat catgatattg gctgaaaagt tctacattct attattgtat
3541 tgtaacacac atgtattgat gattttcatt aagagtttca gattaacttt gaaaaatatt
3601 ccacatggta atcttataaa ttctgtttaa ttacatctgt aaatattatg tgtgtgatag
3661 tattcaataa agtaaaatca aattgtcaaa aaaaaaaaaa aaa
MSUD Type II
E2
mRNA sequence
1 atttccgggg taagatggct gcagtccgta tgctgagaac ctggagcagg aatgcgggga
61 agctgatttg tgttcgctat tttcaaacat gtggtaatgt tcatgttttg aagccaaatt
121 atgtgtgttt ctttggttat ccttcattca agtatagtca tccacatcac ttcctgaaaa
181 caactgctgc tctccgtgga caggttgttc agttcaagct ctcagacatt ggagaaggga
241 ttagagaagt aactgttaaa gaatggtatg taaaagaagg agatacagtg tctcagtttg
301 atagcatctg tgaagttcaa agtgataaag cttctgttac catcactagt cgttatgatg
361 gagtcattaa aaaactctat tataatctag acgatattgc ctatgtgggg aagccattag
421 tagacataga aacggaagct ttaaaagatt cagaagaaga tgttgttgaa actcctgcag
481 tgtctcatga tgaacataca caccaagaga taaagggccg aaaaacactg gcaactcctg
541 cagttcgccg tctggcaatg gaaaacaata ttaagctgag tgaagttgtt ggctcaggaa
601 aagatggcag aatacttaaa gaagatatcc tcaactattt ggaaaagcag acaggagcta
661 tattgcctcc ttcacccaaa gttgaaatta tgccacctcc accaaagcca aaagacatga
721 ctgttcctat actagtatca aaacctccgg tattcacagg caaagacaaa acagaaccca
781 taaaaggctt tcaaaaagca atggtcaaga ctatgtctgc agccctgaag atacctcatt
841 ttggttattg tgatgagatt gaccttactg aactggttaa gctccgagaa gaattaaaac
901 ccattgcatt tgctcgtgga attaaactct cctttatgcc tttcttctta aaggctgctt
961 ccttgggatt actacagttt cctatcctta acgcttctgt ggatgaaaac tgccagaata
1021 taacatataa ggcttctcat aacattggga tagcaatgga tactgagcag ggtttgattg
1081 tccctaatgt gaaaaatgtt cagatctgct ctatatttga catcgccact gaactgaacc
1141 gcctccagaa attgggctct gtgggtcagc tcagcaccac tgatcttaca ggaggaacat
1201 ttactctttc caacattgga tcaattggtg gtacctttgc caaaccagtg ataatgccac
1261 ctgaagtagc cattggggcc cttggatcaa ttaaggccat tccccgattt aaccagaaag
1321 gagaagtata taaggcacag ataatgaatg tgagctggtc agctgatcac agagttattg
1381 atggtgctac aatgtcacgc ttctccaatt tgtggaaatc ctatttagaa aacccagctt
1441 ttatgctact agatctgaaa tgaagactga taagacattc ttgaactttt tgagcttcca
1501 aagagtatgt aaaccctagc tgtgccagca catgttcatc tttacaattt atattgtaaa
1561 cgatttgtat cgtatgatta aggatctaag gcacaatatt tgtcactgtt ctattagact
1621 ttttactgaa aatgaataat ggtgtaatgg ttctcctggg gctgtcacat tttataggtc
1681 agagtgtgac ttcttaatat ggtgctgatg tttttgtgtc aatggcttga aactggcaag
1741 attaacaaaa ttaggccggg catggtggct cacgcctgta atccagcact ttgggaggcc
1801 caggtggggc gatcacctga ggttagaagt ttgagaccag cctggccaac atggtgaaac
1861 ctggcctcta cctaaaaaat acaaaattga ccgggtgtgg tggtgggtac cgctacttgg
1921 gaggctgagg caggagaatc gcttgaacct gggaggtgga ggttgcagtg agctgagatc
1981 gtgctattgc actccagcct gggcgacaga gcaagacgcc atctcaaaaa caaaaaaaac
2041 aaaattcatg ttactaaaag acaggtagcc atatacagac agtatatgcc ctattttttt
2101 taactgactc ttaatgaaac tttaatttta cttaattaag aaatggaatt tatatacaaa
2161 aatattttcc atttccgtta ttatgctaat tgttgtatga aataagtgca attatacttc
2221 tcttttgaga tatccaagag tatattcttg ctctgtatag agaatatcat ctgatagtgt
2281 cttatttata ttaattaatg tctttgaaaa gggaaaagta taaactggcc ttaaaattgt
2341
2401
2461
2521
2581
2641
2701
2761
2821
2881
2941
3001
3061
3121
3181
3241
3301
3361
3421
3481
ccaattatag ttttataacc agtctattaa aggtgtttgt ttaaaatgga tatagtttta
gatttgtggt aatgctttgg tattttcttg gggaagacct tcacctttgc aaacttccct
catgtaagga aggtacttta aatgtagcag ccactgacat ttcttttttt aaaaaaaatt
tgagaagtct acttcctttt aacttttttg gtcttcagct aaaaaatagg ataagaaatt
aaggtctatt ccattctcca tatcctgggt aagaatgtaa ataagaggag aaggaagagt
ctaatagtaa ttatggatat aaaaaataag aaattttgta tagaaatgaa ggtttcataa
tgatcatttt gttaaaggtc tactttaatc agaaatagca acgagatgaa tgtatccaac
atttcaattt gcattcggaa atccatgttg tttctaatat tgtccagttg aaaactgtat
gccaaaatta gttgtttaag tgaagttttg tgacagaaaa aaggttgttt taatatctac
ttggtttttc tcaaaatgga aataatttta aaatcaggaa agaataaatc agccaggtgt
gatgacttgt aactgtaatc ccagttatag gggaggctga agcaggagga tcacttgagg
ccaggagttt gagaccagcc tgggcaacat agtgagatcc catctcaaaa aacattattt
ttaaaattag cctggtggct cacgcctgta atcccagcac tttgggaggc cgaggtggcc
agatcacctg aggtcaggag ttcgagacca ccctggccaa catggtgaaa ccccatctct
acagttttgt aaaaatacaa aaattacctg ggcctggtgc acaggcctgt agtcccagct
acttgggagg ctgaggcagg agaattgctt gagcccaaga ggtggaggtt acagtgagca
gagatcacac cactgcactc cagcctgggt ggcagagcaa cacttcgtct cagaaaaaaa
aaaaaaaacc aaaaaccaaa aagccaagtg tggtggtgtg cacctatagt cccagctact
caggaagctg agacaagagg atcaattgag cccaggagtt caaagctgta gtgagctgtc
attgtgccac tatcctccag tatgggtgac agagtgagac ctggtctcta aaaat
Protein sequence
MAAVRMLRTWSRNAGKLICVRYFQTCGNVHVLKPNYVCFFGYPSFKY
SHPHHFLKTTAALRGQVVQFKLSDIGEGIREVTVKEWYVKEGDTVSQF
DSICEVQSDKASVTITSRYDGVIKKLYYNLDDIAYVGKPLVDIETEALKD
SEEDVVETPAVSHDEHTHQEIKGRKTLATPAVRRLAMENNIKLSEVVG
SGKDGRILKEDILNYLEKQTGAILPPSPKVEIMPPPPKPKDMTVPILVSK
PPVFTGKDKTEPIKGFQKAMVKTMSAALKIPHFGYCDEIDLTELVKLRE
ELKPIAFARGIKLSFMPFFLKAASLGLLQFPILNASVDENCQNITYKASH
NIGIAMDTEQGLIVPNVKNVQICSIFDIATELNRLQKLGSVGQLSTTDLT
GGTFTLSNIGSIGGTFAKPVIMPPEVAIGALGSIKAIPRFNQKGEVYKAQ
IMNVSWSADHRVIDGATMSRFSNLWKSYLENPAFMLLDLK
MSUD Type II - Mutations
Exon(e)/Intron(i)
Codon
Mutation
Consequence
7 (e)
215
TTT → TGT
Phe → Cys
4 (i)
-
-
17-bp insertion,
frameshift
8 (e)
-
AGgt → AAgt
Exon 8 deletion
-
-
15 to 20-bp deletion
-
8 (i)
-
AGgt → AGt
Exon 8 deletion
2 (e)
-
-
Exon 2 deletion
2 (e)
-
CATG → CG
Frameshift
6 (e)
163
GAA → TAA
Glu → Ter
4 (e)
77
CAT → TAT
Ile → Thr
5 (i)
-
ATgta → Ata
Exon 5 deletion
MSUD Type III
E3
mRNA sequence
1 gcgcagggag gggagacctt ggcggacggc ggagccccag cggaggtgaa agtattggcg
61 gaaaggaaaa tacagcggaa aaatgcagag ctggagtcgt gtgtactgct ccttggccaa
121 gagaggccat ttcaatcgaa tatctcatgg cctacaggga ctttctgcag tgcctctgag
181 aacttacgca gatcagccga ttgatgctga tgtaacagtt ataggttctg gtcctggagg
241 atatgttgct gctattaaag ctgcccagtt aggcttcaag acagtctgca ttgagaaaaa
301 tgaaacactt ggtggaacat gcttgaatgt tggttgtatt ccttctaagg ctttattgaa
361 caactctcat tattaccata tggcccatgg aacagatttt gcatctagag gaattgaaat
421 gtccgaagtt cgcttgaatt tagacaagat gatggagcag aagagtactg cagtaaaagc
481 tttaacaggt ggaattgccc acttattcaa acagaataag gttgttcatg tcaatggata
541 tggaaagata actggcaaaa atcaagtcac tgctacgaaa gctgatggcg gcactcaggt
601 tattgataca aagaacattc ttatagccac gggttcagaa gttactcctt ttcctggaat
661 cacgatagat gaagatacaa tagtgtcatc tacaggtgct ttatctttaa aaaaagttcc
721 agaaaagatg gttgttattg gtgcaggagt aataggtgta gaattgggtt cagtttggca
781 aagacttggt gcagatgtga cagcagttga atttttaggt catgtaggtg gagttggaat
841 tgatatggag atatctaaaa actttcaacg catccttcaa aaacaggggt ttaaatttaa
901 attgaataca aaggttactg gtgctaccaa gaagtcagat ggaaaaattg atgtttctat
961 tgaagctgct tctggtggta aagctgaagt tatcacttgt gatgtactct tggtttgcat
1021 tggccgacga ccctttacta agaatttggg actagaagag ctgggaattg aactagatcc
1081 tagaggtaga attccagtca ataccagatt tcaaactaaa attccaaata tctatgccat
1141 tggtgatgta gttgctggtc caatgctggc tcacaaagca gaggatgaag gcattatctg
1201 tgttgaagga atggctggtg gtgctgtgca cattgactac aattgtgtgc catcagtgat
1261 ttacacacac cctgaagttg cttgggttgg caaatcagaa gagcagttga aagaagaggg
1321 tattgagtac aaagttggga aattcccatt tgctgctaac agcagagcta agacaaatgc
1381 tgacacagat ggcatggtga agatccttgg gcagaaatcg acagacagag tactgggagc
1441 acatattctt ggaccaggtg ctggagaaat ggtaaatgaa gctgctcttg ctttggaata
1501 tggagcatcc tgtgaagata tagctagagt ctgtcatgca catccgacct tatcagaagc
1561 ttttagagaa gcaaatcttg ctgcgtcatt tggcaaatca atcaactttt gaattagaag
1621 attatatatt tttttttctg aaatttcctg ggagcttttg tagaagtcac attcctgaac
1681 aggatattct cacagctcca agaatttcta ggactgaatt atgaaacttt tggaaggtat
1741 ttaataggtt tggacaaaat ggaatactct tatatctata ttttacataa atttagtatt
1801 ttgtttcagt gcactaatat gtaagacaaa aaggactact tattgtagtc atcctggaat
1861 atctccgtca actcatattt tcatgctgtt catgaaagat tcaatgcccc tgaatttaaa
1921 tagctctttt ctctgataca gaaaagttga attttacatg gctggagcta gaatttgata
1981 tgtgaacagt tgtgtttgaa gcacagtgat caagttattt ttaatttggt tttcacattg
2041 gaaacaagtc agtcattcag atatgattca aatgtctata aaccaaactg atgtaagtaa
2101 atggtctctc acttgtttta tttaacctct aaattctttc attttagggg tagcatttgt
2161 gttgaagagg ttttaaagct tccattgttg tctgcaactc tgaagggtaa ttatatagtt
2221 acccaaatta agagagtcta tttacggaac tcaaatacgt gggcattcaa atgtattaca
2281 gtggggaatg aagatactga aataaacgtc ttaaatattc
Protein Sequence
MQSWSRVYCS LAKRGHFNRI SHGLQGLSAV
PLRTYADQPI DADVTVIGSG PGGYVAAIKA
AQLGFKTVCI EKNETLGGTC LNVGCIPSKA
LLNNSHYYHM AHGTDFASRG IEMSEVRLNL
DKMMEQKSTA VKALTGGIAH LFKQNKVVHV
NGYGKITGKN QVTATKADGG TQVIDTKNIL
IATGSEVTPF PGITIDEDTI VSSTGALSLK
KVPEKMVVIG AGVIGVELGS VWQRLGADVT
AVEFLGHVGG VGIDMEISKN FQRILQKQGF
KFKLNTKVTG ATKKSDGKID VSIEAASGGK
AEVITCDVLL VCIGRRPFTK NLGLEELGIE
LDPRGRIPVN TRFQTKIPNI YAIGDVVAGP
MLAHKAEDEG IICVEGMAGG AVHIDYNCVP
SVIYTHPEVA WVGKSEEQLK EEGIEYKVGK
FPFAANSRAK TNADTDGMVK ILGQKSTDRV
LGAHILGPGA GEMVNEAALA LEYGASCEDI
ARVCHAHPTL SEAFREANLA ASFGKSINF
Exon
Codon
Mutation
Consequence
N/A
37
AAA → GAA
Lys → Glu
N/A
453
CCG → CTG
Pro → Leu
Metabolic functions


Branched chain dehydrogenase complex
(BCKAD)
 3 catalytic components: branched-chain
alpha-keto acid decarboxylase (E1),
lipoamide acyltransferase (E2) and
lipoamide dehydrogenase (E3)
 2 regulatory enzymes: kinase and
phosphotase
 Encoded by 6 genetic loci
 Mutation in any of the loci can result in
defect
Defect in BCKAD causes a block in BCKA
oxidative decarboxylation
 Accumulation of BCKA
(1) transamination by BCAA amino transferase
(2) oxidative decarboxylation by BCKAD
(3) dehydrogenation by isovaleryl-CoA dehydrogenase
(4) dehydrogenation by alpha-methyl branched chain
cyl-CoA dehydrogenase
(Chuang & Shih, 1995)
Screening and Diagnosis


Prenatal diagnosis
 analysis of cultured amniocytes obtained at mid-trimester
amniocentesis
 direct analysis of tissues or cultured cells from chorionic villi sample
taken during first trimester
 Use allele-specific oligonucleotide (ASO) probe following PCR to detect
mutation in DNA obtained from amniocytes
 Attempts at measuring amniotic fluid concentration of BCAA, BCKA
and α-hydroxyacids have been unsuccessful
Routine newborn screening
 Guthrie bacterial inhibition assay
Increase leucine levels in blood spots
Detect classic, intermediate and E3-deficient MSUD but intermediate
may be missed due to lower leucine levels than classic
 Tandem mass spectroscopy coupled with fast atom bombardment
(FAB) ionisation
Detect organic acids and amino acids abnormalities in blood and
urine
samples on filter paper
Screening and Diagnosis cont.

General diagnosis or genetic studies
 Urine 2,4-dinitrophenylhydrazine (DNPH) test
 Gas chromatographic mass spectroscopy (GC-MS)
 Enzymic studies of cell cultures (skin fibroblasts and lymphoblasts)
 Allele-specific oligonucleotide (ASO) probing
Historical perspective

Diagnosis relied on the recognition of clinical symptoms and signs and
Chemical and enzymological analysis were performed if indicated
(Galjaard 1980)
Therapies and Management
Long term dietary management
 Restrict intake of BCAA in diet to
the amount essential for growth
 Start as soon as possible and
continue for life
 Treat classic and intermediate
MSUD patients the same way
 For intermittent MSUD, decrease
protein intake during episodes
 Monitor plasma BCAA levels
weekly for the first 6 months and
keep as close to normal as
possible
 A trial of thiamine therapy is
recommended to determine
thiamine responsiveness in all
new patients
History of dietary therapies
Dietary therapies started in 1959.
Gelatin has low BCAA and was
used as a source of BCAA in
England in the early days. A
synthetic formula was developed by
Snyderman et al in the United
States which consisted of 18 amino
acids (based on breastmilk
composition) carbohydrates, fat,
minerals and vitamins. Based on
this formula, other commercial
medical diets have since been
created.
Therapies and Management cont.
Acute-phase management
 Infection and stress can cause a significant accumulation of BCAA and BCKA
which can be life threatening
 Treatment involves:

Rapid removal of toxic metabolites
Exchange transfusion (early 1960’s) achieved limited success
Peritoneal dialysis (1969) produced significant improvement within hours.
It is simple to implement and has become an established procedure for
treating patients in crisis
Hemodialysis is equally successful but requires specialised equipment
and personnel
Continuous arteriovenous hemoperfusion can be used for adults but
has technical limitations when applied to newborns

Parenteral Nutritional therapy
BCAA-free L-amino acid mixture combined with glucose, lipid, electrolytes
and vitamins

Minimise catabolic state and/or promote anabolism
use insulin and carbohydrate to promote anabolism
Therapies and Management cont.
Other therapies
 Introducing subunits of BCKDH enzyme into cells using a retrovirous
 Liver transplant
 Somatic gene therapy
Key References





Bondy, P.K. & Rosenberg, L.C. 1980, Metabolic Control and Disease, 8th
Edition, W.B. Saunders Company, Philadelphia
Galjaard, H. 1980, Genetic Metabolic Diseases: Early Diagnosis and
Prenatal Analysis, Elsevier/North-Holland Biomedical Press, Amsterdam
Chuang, D.T. & Shih, V.E. 1995, ‘Disorders of Branched Chain Amino Acid
and Keto Acid Metabolism’, in The Metabolic and Molecular Bases of
Inherited Diseases, vol. 1, 7th Edition, eds Scriver et al., McGraw-Hill, New
York
OMIM, URL: http://www3.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=248600
Ensemble, URL:
http://www.ensembl.org/homo_sapians/genereview?gene=ENSG000001379
92 (ENSG00000142046, ENSG00000083123, ENSG00000091140)