Novel Mutation May Be Unrecognized Cause of Sudden Infant Death

Megan Brooks

August 24, 2021

A previously healthy infant who survived sudden cardiac arrest at home was later found to have a de novo likely pathogenic genetic mutation in the SOS1 gene, which might be an unrecognized cause of sudden infant death, report clinicians from Missouri.

SOS1 gene variants are associated with Noonan syndrome, a genetic disorder that affects the RAS/MAPK signalling pathway. However, on presentation, the infant had none of the usual structural cardiac findings typical of Noonan syndrome, such as valvular disease or hypertrophic cardiomyopathy.

"To date, this is the first case reported of a ventricular fibrillation arrest in a patient with a RASopathy-related variant prior to development of the typically associated structural cardiac phenotype and may represent a previously unrecognized etiology of sudden death during infancy," write Christopher W. Follansbee, MD, and Lindsey Malloy-Walton, DO, from the Ward Family Heart Center, Children's Mercy Kansas City, and the University of Missouri School of Medicine.

"Genetic testing in cases of unexplained aborted or sudden cardiac deaths, even in previously healthy children, can be valuable in establishing a diagnosis, determining the prognosis, and assessing risk to family members," they add in a news release.

Follansbee and Malloy-Walton describe the case in a report published in the August issue of HeartRhythm Case Reports.

Case Details

The case involved a 2-month-old girl who did not wake up as usual for her morning feeding. Her mother found her limp, pale, and having difficulty breathing.

When emergency medical services arrived, the infant had no pulse. Cardiopulmonary resuscitation was initiated and an external defibrillator revealed coarse ventricular fibrillation. An initial shock of 10 J was given with conversion to an atrial rhythm with aberrant ventricular conduction.

The infant developed increasing frequency of ectopy before degenerating to ventricular fibrillation. A second shock with 20 J was unsuccessful, but a third shock of 20 J successfully converted the rhythm to sinus with aberrant ventricular conduction and atrial ectopy with return of spontaneous circulation.

In the ICU, the infant displayed incessant, nonsustained ectopic atrial tachycardia, with rapid episodes of ectopic atrial tachycardia with ventricular rates up to 300 beats per minute in the setting of seizure activity, they report. 

With intravenous lorazepam, seizure activity resolved and treatment with amiodarone boluses led to transient establishment of sinus rhythm.

The QTc was noted to be above 500 ms and Brugada positioning of leads was unrevealing, the authors note.

Transthoracic echocardiogram showed a structurally normal heart with normal valve morphology and a patent foramen ovale with left-to-right flow. The initial ejection fraction was 49%. There was no evidence of ventricular hypertrophy, dilation, or noncompaction.

The infant was started on an esmolol infusion titrated to 225 μg/kg per min with frequent, nonsustained breakthrough of ectopic atrial tachycardia. Over the next 24 hours, the QTc interval normalized with normal T-wave morphology.

A procainamide challenge was negative. Cardiac MRI revealed normalization of ventricular function.

The genetics team was called in and a standard three-generation family history was obtained. An older sibling, 2 years of age, had no known medical conditions. The child's paternal grandfather had died of a presumed myocardial infarction in his 50s, but no autopsy had been performed.

There was no family history of congenital heart disease, arrhythmia, sudden death, cardiomyopathy, recurrent syncope, congenital deafness, seizure, miscarriage, or developmental delay. Electrocardiograms obtained on the parents were normal.

Genetic testing using a comprehensive arrhythmia and cardiomyopathy next-generation sequencing panel revealed a de novo likely pathogenetic variant of the SOS1 gene associated with Noonan syndrome.

Given the aborted sudden cardiac death, the patient underwent dual-chamber epicardial implantable cardioverter-defibrillator implantation prior to discharge.

Follansbee and Malloy-Walton say a limitation to the case report is the lack of definitive association of the SOS1 variant with the presentation.

However, knowing the infant has the SOS1 variant and a history of aborted sudden death will allow for "monitoring and early intervention on typical manifestations of Noonan syndrome as the patient grows," they say.

This research had no specific funding. Follansbee and Malloy-Walton have disclosed no relevant conflicts of interest.

HeartRhythm Case Rep. 2021;7:510-513. Full text


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