Two novel mutations in the BCKDK (branched-chain keto-acid dehydrogenase kinase) gene are responsible for a neurobehavioral deficit in two pediatric unrelated patients.
Inactivating mutations in the BCKDK gene, which codes for the kinase responsible for the negative regulation of the branched-chain α-keto acid dehydrogenase complex (BCKD), have recently been associated with a form of autism in three families. In this work, two novel exonic BCKDK mutations, c.520C>G/p.R174G and c.1166T>C/p.L389P, were identified at the homozygous state in two unrelated children with persistently reduced body fluid levels of branched-chain amino acids (BCAAs), developmental delay, microcephaly, and neurobehavioral abnormalities. Functional analysis of the mutations confirmed the missense character of the c.1166T>C change and showed a splicing defect r.[520c>g;521_543del]/p.R174Gfs1*, for c.520C>G due to the presence of a new donor splice site. Mutation p.L389P showed total loss of kinase activity. Moreover, patient-derived fibroblasts showed undetectable (p.R174Gfs1*) or barely detectable (p.L389P) levels of BCKDK protein and its phosphorylated substrate (phospho-E1α), resulting in increased BCKD activity and the very rapid BCAA catabolism manifested by the patients' clinical phenotype. Based on these results, a protein-rich diet plus oral BCAA supplementation was implemented in the patient homozygous for p.R174Gfs1*. This treatment normalized plasma BCAA levels and improved growth, developmental and behavioral variables. Our results demonstrate that BCKDK mutations can result in neurobehavioral deficits in humans and support the rationale for dietary intervention.
Department of Neurology, Hospital Sant Joan de Déu (HSJD), CIBER de Enfermedades Raras (CIBERER), Barcelona, Spain.
Angels
A
García-Cazorla
Alfonso
A
Oyarzabal
Joana
J
Fort
Concepción
C
Robles
Esperanza
E
Castejón
Pedro
P
Ruiz-Sala
Susanna
S
Bodoy
Begoña
B
Merinero
Anna
A
Lopez-Sala
Joaquín
J
Dopazo
Virginia
V
Nunes
Magdalena
M
Ugarte
Rafael
R
Artuch
Manuel
M
Palacín
Pilar
P
Rodríguez-Pombo
Patricia
P
Alcaide
Rosa
R
Navarrete
Paloma
P
Sanz
Mariona
M
Font-Llitjós
Ma Antonia
MA
Vilaseca
Aida
A
Ormaizabal
Anna
A
Pristoupilova
Sergi Beltran
SB
Agulló
D000597:Amino Acids, Branched-Chain / Q000008:administration & dosage / Q000097:blood; D002658:Developmental Disabilities / Q000178:diet therapy / Q000235:genetics*; D005347:Fibroblasts / Q000201:enzymology; D006801:Humans; D008297:Male; D020125:Mutation, Missense; D009422:Nervous System Diseases / Q000178:diet therapy / Q000235:genetics*; D010372:Pediatrics; D011494:Protein Kinases / Q000172:deficiency / Q000235:genetics*
D000597:Amino Acids, Branched-Chain; D011494:Protein Kinases; C035627:(3-methyl-2-oxobutanoate dehydrogenase (lipoamide)) kinase
BCKDK; branched-chain keto-acid dehydrogenase complex; dietary treatment; neurobehavioral deficit