hide
Free keywords:
Adolescent
Adult
Amino Acid Sequence
Catalytic Domain
Child
Child, Preschool
Computer Simulation
DNA Mutational Analysis
European Continental Ancestry Group/genetics
Exome
Female
*Genes, Recessive
Histamine N-Methyltransferase/*genetics/metabolism
Humans
Infant
Intellectual Disability/enzymology/*genetics
Iraq
Male
Molecular Sequence Data
*Mutation, Missense
Pedigree
Sequence Alignment
Turkey
Abstract:
Histamine (HA) acts as a neurotransmitter in the brain, which participates in the regulation of many biological processes including inflammation, gastric acid secretion and neuromodulation. The enzyme histamine N-methyltransferase (HNMT) inactivates HA by transferring a methyl group from S-adenosyl-l-methionine to HA, and is the only well-known pathway for termination of neurotransmission actions of HA in mammalian central nervous system. We performed autozygosity mapping followed by targeted exome sequencing and identified two homozygous HNMT alterations, p.Gly60Asp and p.Leu208Pro, in patients affected with nonsyndromic autosomal recessive intellectual disability from two unrelated consanguineous families of Turkish and Kurdish ancestry, respectively. We verified the complete absence of a functional HNMT in patients using in vitro toxicology assay. Using mutant and wild-type DNA constructs as well as in silico protein modeling, we confirmed that p.Gly60Asp disrupts the enzymatic activity of the protein, and that p.Leu208Pro results in reduced protein stability, resulting in decreased HA inactivation. Our results highlight the importance of inclusion of HNMT for genetic testing of individuals presenting with intellectual disability.
