Two Novel Mutations in theBCKDK(Branched-Chain Keto-Acid Dehydrogenase Kinase) Gene Are Responsible for a Neurobehavioral Deficit in Two Pediatric Unrelated Patients

Abstract

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.

Thiamine transporter-2 deficiency: outcome and treatment monitoring

“…The coding region and the flanking intron-exon boundaries were PCR amplified with primers based on the Ensembl genome browser entry ENSG00000135917. The amplicons were sequenced and analyzed as previously described [24]. The mutation nomenclature used follows that described at http://www.hgvs.org./mutnomen/.…”

Sodium phenylbutyrate decreases plasma branched-chain amino acids in patients with urea cycle disorders

“…Longitudinal analyses involving BCAA levels and hyperammonemia episodes are necessary to test whether the decrease in BCAA, especially in those with BCAA deficiency, increases risk for hyperammonemia. Another concern of long-term BCAA deficiency is that it could lead to detrimental neurologic outcomes even in the absence of metabolic decompensation [16, 17]. Patients with biallelic mutations in branched-chain ketoacid dehydrogenase kinase (BCKDK) and low plasma BCAA have neurocognitive phenotypes [16, 17].…”

“…Another concern of long-term BCAA deficiency is that it could lead to detrimental neurologic outcomes even in the absence of metabolic decompensation [16, 17]. Patients with biallelic mutations in branched-chain ketoacid dehydrogenase kinase (BCKDK) and low plasma BCAA have neurocognitive phenotypes [16, 17]. Corroborating these human data, a mouse model of BCKDK deficiency exhibits seizures, tremors, lower plasma and brain levels of BCAAs and elevations in other large neutral amino acids [17].…”

A web-based interactive framework to assist in the prioritization of disease candidate genes in whole-exome sequencing studies

“…More than 800 exomes of patients of more than 70 different inherited pathologies, produced by the Spanish Network for Research in Rare Diseases (CIBERER, http://www.ciberer.es) and the Medical Genome Project (MGP; http://www.medicalgenomeproject.com), have been analyzed using BiERapp. Recent publications include the discovery of two new mutations in the BCKDK gene, responsible of a neurobehavioral deficit in pediatric patients (28), new mutations in different genes causing inherited retinal dystrophies (29–32) and metabolic diseases (33). …”