Introduction

Truncus arteriosus is a rare hereditary heart defect in which there is no separation of the pulmonary artery and aortic artery, originating from the heart for blood supply to different parts of the body. Truncus Arteriosus results in a single large blood vessel that arises from the heart, where both oxygenated and deoxygenated blood mix. Hence, there is no proper supply of oxygen-rich blood to the body. This occurs during fetal heart development.¹ 

Symptoms that typically involve infants include cyanosis, respiratory distress, and heart failure.¹ Advanced prenatal imaging and genetic testing have an important role in early diagnosis and management.¹ Early surgical intervention is typically required to correct the defect, i.e. separate blood flow, and improve survival rates.²

Genetic basis of truncus arteriosus

The genetic cause of this disorder is complex and multifactorial. 22q11.2 deletion syndrome, or DiGeorge syndrome, is a common genetic cause and makes up to 35% of the genetic causes of truncus arteriosus.

According to recent studies, changes in genes TBX1, GATA6, and NKX2-5 have also been identified as the reason for truncus arteriosus. These genes play an important role in heart development. Inherited and environmental factors are also contributors suggested by the familial cases of truncus arteriosus.^3,4,5

In future, such an understanding of genetic causes will ensure appropriate diagnosis, counselling, and proper therapeutic measures targeted to that patient group.

Genetic syndromes and truncus arteriosus

This condition is often associated with specific genetic syndromes

DiGeorge syndrome

DiGeorge syndrome, also known as 22q11.2 deletion syndrome, is associated with 12% to 35% of cases of truncus arteriosus. The TBX1 gene within this region of the chromosome plays a significant role in cardiac development, and its deletion can result in congenital heart defects, including truncus arteriosus.³

CHARGE syndrome

Mutations in the CHD7 gene cause CHARGE syndrome. It is characterised by a combination of congenital anomalies, such as heart defects, including truncus arteriosus.⁶

VACTERL association

VACTERL association is a non-random collection of birth defects that may involve cardiac abnormalities like truncus arteriosus.⁶

Transcription factor gene variants

Truncus arteriosus has been seen with mutations in the genes encoding transcription factors like GATA4, GATA6, NKX2-5, and NKX2-6.⁶

Diagnosis and genetic testing

Accurate diagnosis and genetic evaluation are crucial for effective management and counselling.

Prenatal diagnosis

Advances in fetal imaging, especially in fetal echocardiography, have significantly improved the prenatal diagnosis of truncus arteriosus. This modality enables one to visualise a single arterial trunk overriding a large ventricular septal defect, allowing for early diagnosis and planning of postnatal care.¹

Postnatal diagnosis

After birth, the diagnosis is confirmed with the help of echocardiography, which shows detailed imaging of the heart structure and function; imaging modalities such as computed tomography or magnetic resonance imaging help assess anatomy and plan interventions.⁷

Genetic testing

Genetic testing has been very significant in the determination of underlying syndromes for truncus arteriosus. The most common genetic association found with truncus arteriosus is 22q11.2 deletion syndrome, which has a prevalence rate of about 12–35%.

Other syndromes associated with truncus arteriosus are CHARGE syndrome and VACTERL association. Karyotyping and fluorescence in situ hybridisation (FISH) have been used for chromosomal abnormality detection. Targeted gene sequencing can determine specific mutations.³

Clinical implications

Identifying genetic syndromes associated with truncus arteriosus is essential for:

• Family counselling: Understanding the genetic basis helps to assess recurrence risks for future pregnancies
• Management planning: Some syndromes may affect the timing of surgical interventions
• Long-term surveillance: Some genetic disorders are associated with other systemic anomalies and require surveillance

In summary, early and accurate diagnosis of truncus arteriosus through genetic evaluation is vital for optimising patient outcomes and providing informed counselling.

Management

Since truncus arteriosus is a rare congenital heart defect that results in one common arterial trunk from the heart to supply both systemic and pulmonary circulations, various steps are taken to manage it.

Interventions

This intervention requires early surgical repair, which should be done after a few weeks of birth. The procedure is carried out to separate the pulmonary arteries from the common arterial trunk and connect them to the right ventricle using a conduit. 

The same procedure closes the ventricular septal defect; hence, it helps develop a separate systemic and pulmonary circulation.¹

Medical management

In preparation for surgery, it is often necessary to stabilise heart failure symptoms through medication, including the use of diuretics to reduce fluid overload and inotropic agents to enhance cardiac function.¹

Long-term follow-up

Lifelong cardiology follow-up is indicated because complications include conduit obstruction or leakage, arrhythmias, and re-interventions with the growth of the child.¹

Prognosis

Surgical outcomes 

Advances in surgery have greatly reduced mortality. While there is considerable variability in follow-up studies for infants who received early repair for truncus arteriosus, the survival for this group now approaches 90%.¹

Impact of genetic syndromes 

Genetic syndromes such as the 22q11.2 deletion syndrome carry a worse prognosis. These also are associated with other congenital anomalies and mental retardation in many cases; therefore, full multidisciplinary care is recommended.⁸

Outcomes 

Children with truncus, especially those with associated genetic syndromes, have an increased predisposition to neurodevelopmental challenges. Early assessments and interventions should be made for optimal growth and development.⁹

Early surgical intervention and comprehensive management have dramatically improved outcomes in patients with truncus arteriosus. The presence of associated genetic syndromes demands a tailored, multidisciplinary approach to deal with the broader spectrum of health needs and optimise prognosis.

Research and future directions

Recent research

Advances in prenatal imaging, especially fetal echocardiography, have significantly enhanced the early identification of truncus arteriosus. Early diagnosis gives a chance to counsel parents regarding the outcome and available opportunities.

It also helps plan delivery at a tertiary care centre where specialised services for neonatology and cardiothoracic surgical procedures are accessible.

Studies based on genetic investigation have described the role of 22q11.2 microdeletion in truncus arteriosus. Such genetic changes affect multiple clinical symptoms, including immune deficiency, hypocalcemia, and developmental delay.

Early genetic evaluation enables proper preparation for those genetic factors, along with the relevant prenatal monitoring and establishment of targeted strategies to deal with the involved comorbidity.¹

Future directions

Advanced genetic testing 

Advanced genetic testing in prenatal care has further improved the ability to detect associated genetic abnormalities, thus refining risk stratification and decision making in finalising the treatment.¹

Multidisciplinary approach 

An improvement in the outcome of individuals with truncus arteriosus can only be achieved by coordinated, multidisciplinary management from prenatal diagnosis to postnatal care.

The medical and surgical care, in combination with continuous research, will continue to address the challenges posed by this complex congenital heart defect and improve the prognosis and quality of life of the affected individuals.¹

Long-term follow-up studies

Long-term studies are needed to track patients from prenatal diagnosis, through childhood into adulthood, to understand the outcomes of truncus arteriosus in a better way, and how future management can be carried out.¹

Summary

Truncus arteriosus is most commonly associated with congenital syndromes, especially 22q11.2 deletion syndrome or DiGeorge syndrome in 12–35% of cases. Other syndromes include CHARGE and VACTERL associations. The TBX1 gene, integral to normal cardiac development, is often implicated.

Diagnosis is made by fetal or postnatal echocardiography, with genetic testing to confirm the presence of a specific underlying syndrome. Management is by early surgical repair, medical stabilisation, and lifelong follow-up due to potential complications.

Prognosis is favourable with early intervention, although associated genetic syndromes may impact long-term outcomes, including neurodevelopmental delays. Multidisciplinary care is essential for optimal patient management.