[DNA-based diagnostics of long QT syndrome]

BACKGROUND

Long QT syndrome is characterised by inherited long QT interval on the ECG and increased risk for syncope and sudden death caused by arrhythmias. For Romano-Ward syndrome and Jervell and Lange-Nielsen syndrome DNA based diagnostics are available.

MATERIALS AND METHODS

This paper is a summary of our experience with DNA-based diagnostics of LQTS since the autumn of 2003. The diagnostic analyses are performed by sequencing the exons of five genes, KCNQ1, HERG, SCN5A, minK and MiRP1.

RESULTS AND INTERPRETATIONS

As of mid-January 2005, 56 probands with long QT syndrome have been referred for genetic testing. We have identified an underlying mutation in 64% of the patients. Mutations in the KCNQ1 gene are most frequent in Norwegian long QT syndrome patients, as 61% of the patients have their mutation in this gene. The detection of a mutation in the probands has led to genetic testing of 215 relatives; 99 out of these are heterozygous for the mutation present in the family. Heterozygous patients have been referred to a cardiologist. Of the 43 that have been referred to follow up at the department of cardiology at Rikshospitalet, 35 have started treatment with beta blockers to reduce the risk of arrhythmias. Thus, DNA-based diagnostics has clinical significance leading to prophylactic treatment of long QT syndrome patients. Compared to evaluation of ECG, which is negative in 30% of mutation carriers, the sensitivity of DNA-based diagnostics of relatives of probands with a known mutation, is close to 1.

[Cardiac ion channel disorders--diagnosis and treatment]

BACKGROUND

Inherited arrhythmogenic disorders are a group of genetically determined diseases characterised by ventricular tachyarrhythmias sometimes leading to sudden death. The molecular bases of these disorders are mutations in genes coding for various cardiac ion channels. The most common cardiac ion channel disease is the long QT syndrome. This syndrome is rare, but probably more common in Norway than previously expected. We have recently started genetic testing for cardiac ion channel disorders at Rikshospitalet University Hospital in Oslo. This review describes the current understanding of the etiology, prognosis and management of cardiac ion channel disorders, based on literature and our own clinical experience.

INTERPRETATION

Cardiac ion channel disorders may lead to sudden cardiac death. Prophylactic and life-saving therapies are available for many of these disorders. Therapy and risk stratification depend on the clinical presentation, the ECG pattern, and which gene is mutated. Genetic testing offers the opportunity to exclude individual family members as mutation carriers.

Patent ductus venosus does not lead to alimentary galactosaemia in preterm infants

The aim of this study was to investigate if an open ductus venosus representing a portal-caval shunt can lead to transient "alimentary galactosaemia" in preterm infants fed human breast milk. Twenty-six preterm infants (28-34 wk of gestational age) with open ductus venosus were included. Capillary blood samples for measurement of galactose and glucose were collected before, 30 and 50 min after a meal with breast milk (range 12-23 mL/kg). Ultrasound studies of the blood flow in the ductus venosus, truncus coeliacus, superior mesenteric artery and left hepatic vein were performed before and 30 min after the meal. There was a significant rise in blood glucose after 30 and 50 min, indicating a sufficient lactose load. Galactose, however, was either not detectable or was just above the detectable limit (0.1-0.4 mmol/L), with no changes after the meal. An increased flow velocity was found in the ductus venosus and superior mesenteric artery after 30 min (p < or = 0.001) indicating increased entero-hepatic and portal-caval shunting.

CONCLUSION

A patent ductus venosus does not lead to a significant hypergalactosaemia in preterm infants fed human breast milk. Thus, in respect to breast-milk feeding, this is regarded safe in healthy preterm infants even with an open ductus venosus. The increased portal-caval shunting may, however, influence the hepatic metabolism of other enterally absorbed substances.

A comparison between haematological parameters in 'capillary' and venous blood samples from hospitalized children aged 3 months to 14 years

In 16 hospitalized children aged 3 months to 14 years EDTA-blood samples were taken simultaneously from an anticubital vein and from a finger tip. Haematological measurements were subsequently performed in an Ortho ELT 800/WS analyzer. The thrombocyte count and the red cell indices were nearly identical in the two sets of samples. The 'capillary' erythrocyte count, haematocrit and haemoglobin values exceeded those of venous blood by 2%, and the mean 'capillary' total leukocyte count by about 20%. The relative frequency of lymphocytes, granulocytes and mononuclear cells did not alter between the two sets of samples. The significant differences demonstrated may in certain clinical settings be of medical importance. Their possible explanations are discussed.