Background-In the congenital long-QT syndrome (LQTS), there can be a marked phenotypic heterogeneity. Founder effects, by which many individuals share a mutation identical by descent, represent a powerful tool to further understand the underlying mechanisms and to predict the natural history of mutation-associated effects. We are investigating one such founder effect, originating in South Africa in approximately AD 1700 and segregating the same KCNQ1 mutation (A341V). Methods and Results-The study population involved 320 subjects, 166 mutation carriers (MCs) and 154 noncarriers.When not taking ␤-blocker therapy, MCs had a wide range of QTc values (406 to 676 ms), and 12% of individuals had a normal QTc (Յ440 ms). A QTc Ͼ500 ms was associated with increased risk for cardiac events (ORϭ4.22; 95% CI, 1.12 to 15.80; Pϭ0.033). We also found that MCs with a heart rate Ͻ73 bpm were at significantly lower risk (ORϭ0.23; 95% CI, 0.06 to 0.86; Pϭ0.035). This study also unexpectedly determined that KCNQ1-A341V is associated with greater risk than that reported for large databases of LQT1 patients: A341V MCs are more symptomatic by age 40 years (79% versus 30%) and become symptomatic earlier (7Ϯ4 versus 13Ϯ9 years, both PϽ0.001). Accordingly, functional studies of KCNQ1-A341V in CHO cells stably expressing IK s were conducted and identified a dominant negative effect of the mutation on wild-type channels. Conclusions-KCNQ1-A341V is a mutation associated with an unusually severe phenotype, most likely caused by the dominant negative effect of the mutation. The availability of an extended kindred with a common mutation allowed us to identify heart rate, an autonomic marker, as a novel risk factor. (Circulation. 2005;112:2602-2610.)

CD5 is a glycoprotein expressed on thymocytes, T cells, and a subset of B cells. Antibody-mediated cross-linking studies or studies on CD5 knockout mice implicate CD5 as a co-stimulatory or negative regulatory molecule. CD5 is rapidly phosphorylated on tyrosine (Y) residues following Tcell activation. Y429 and Y441 occur in an imperfect immunoreceptor tyrosine-based activation motif (ITAM)-like sequence. We investigated whether phosphatidylinositol (PI) 3-kinase, which binds to tyrosine-phosphorylated ITAM, interacts with CD5 following T cell activation. PI 3-kinase activity and the regulatory p85 subunit of PI 3-kinase associated with CD5 in pervanadate-stimulated, but not in unstimulated thymocytes. Cellular p85 as well as the recombinant Src homology 2 (SH2) domains of p85 bound a tyrosine-phosphorylated peptide encompassing Y463 with approximately threefold greater affinity than a doubly tyrosine-phosphorylated Y429-Y441 peptide. Binding of the C-SH2 domain to the Y463 phosphopeptide, together with preferential binding of the N-SH2 domain to the Y429-Y441 phosphopeptide, suggests a bivalent interaction. A 120-kDa phosphoprotein (pp120) associated with CD5 and specifically with the Y429-Y441 phosphopeptide in stimulated thymocytes. We conclude that stimulation of thymocytes with pervanadate induces the recruitment of PI 3-kinase and pp120 to CD5.

Women affected by the common KCNQ1-A341V mutation are at low risk for cardiac events during pregnancy and without excess risk of miscarriage; their infants delivered by C-section because of fetal distress are extremely likely to also be mutation carriers. Beta-blockers remain recommended. These conclusions likely apply to most LQT1 patients.

BackgroundTrichohepatoenteric syndrome (THE-S) or phenotypic diarrhoea of infancy is a rare autosomal recessive disorder characterised by severe infantile diarrhoea, facial dysmorphism, immunodeficiency and woolly hair. It was first described in 1982 in two infants with intractable diarrhoea, liver cirrhosis and abnormal hair structure on microscopy. We report on two siblings from a consanguineous family of Somali descent who, despite extensive clinical investigation, remained undiagnosed until their demise. The index patient died of fulminant cytomegalovirus pneumonitis at 3 months of age.MethodsWhole exome sequencing (WES) was performed on a premortem DNA sample from the index case. Variants in a homozygous recessive state or compound heterozygous state were prioritized as potential candidate variants using TAPER™. Sanger sequencing was done to genotype the parents, unaffected sibling and a deceased sibling for the variant of interest.ResultsExome sequencing identified a novel homozygous mutation (c.4507C > T, rs200067423) in TTC37 which was confirmed by Sanger sequencing in the index case. The identification of this mutation led to the diagnosis of THE-S in the proband and the same homozygous variant was confirmed in a male sibling who died 4 years earlier with severe chronic diarrhoea of infancy. The unaffected parents and sister were heterozygous for the identified variant.ConclusionsWES permitted definitive genetic diagnosis despite an atypical presentation in the index case and suggests that severe infection, likely secondary to immunodeficiency, may be a presenting feature. In addition definitive molecular diagnosis allows for genetic counseling and future prenatal diagnosis, and demonstrates the value of WES for post-mortem diagnosis of disorders with a non-specific clinical presentation in which a Mendelian cause is suspected.Electronic supplementary materialThe online version of this article (doi:10.1186/s12881-017-0388-5) contains supplementary material, which is available to authorized users.