Compound Heterozygous KCNQ1 Mutations Causing Recessive Romano-Ward Syndrome: Functional Characterization by Mutant...

Area of Science:

• Genetics and Molecular Biology
• Cardiovascular Physiology
• Ion Channel Function

Background:

• Next Generation Sequencing identifies KCNQ1 variants in Romano-Ward syndrome, often autosomal dominant but with reported recessive forms.
• Missense KCNQ1 variants require functional studies to determine pathogenicity and disease mechanisms.
• Two compound heterozygous KCNQ1 mutations (p.A300T and p.P535T) were found in a child with sudden death.

Purpose of the Study:

• To investigate the clinical significance and pathogenicity of KCNQ1 variants p.A300T and p.P535T.
• To analyze the biophysical properties and plasma membrane colocalization of wildtype, A300T, and P535T KCNQ1 channels, alone and in combination.

Main Methods:

• Co-expression of wildtype, A300T, and P535T KCNQ1 alleles with the minK subunit in HEK293 cells.
• Analysis of channel colocalization with the plasma membrane.
• Patch-clamp electrophysiology to assess biophysical phenotypes of homo- and heterotetrameric channels.

Main Results:

• A300T homotetramers showed left-shifted activation, decreased conductance, slow rise-time, and use-dependent response.
• A300T's slow rise-time and use-dependent response were dominant traits.
• P535T decreased conductance and Kv7.1-minK colocalization.
• P535T/A300T heterotetramers exhibited decreased colocalization, slow rise-time, and the A300T use-dependent response.
• A300T's voltage dependence was recessive with WT but dominant with P535T.

Conclusions:

• The biophysical properties of P535T/A300T KCNQ1 channels are consistent with recessive Romano Ward syndrome.
• Further biophysical analysis may reveal additional mechanisms in long QT syndrome pathophysiology.