Pectus excavatum (PE), often called “sunken chest” or “funnel chest,” is the most common congenital deformity of the anterior chest wall. This condition is characterized by an inward depression of the sternum and the attached costal cartilages, creating a hollowed appearance. Affecting approximately 1 in every 300 to 1,000 live births, the deformity is often noticeable in childhood but typically becomes more pronounced during adolescence. Current evidence suggests that genetics play a significant, yet complex, role in whether this structural abnormality is passed down.
The Inherited Link
Research strongly indicates a familial predisposition for developing this chest wall deformity, meaning it tends to run in families. Studies show that between 40% and 53% of individuals with pectus excavatum have at least one other family member who shares the condition, suggesting a clear hereditary component. The exact pattern of genetic transmission, however, is not simple and does not always follow classical Mendelian inheritance rules. For many families, the inheritance is thought to be multifactorial or polygenic, meaning it involves the interaction of multiple different genes rather than a single gene mutation. Some family pedigrees have exhibited patterns consistent with autosomal dominant inheritance, often with incomplete penetrance.
Underlying Connective Tissue Mechanism
The physical cause of the sternal depression is an abnormal growth pattern in the costal cartilage, the flexible tissue that connects the ribs to the breastbone. The prevailing hypothesis suggests an overgrowth or unbalanced growth of this cartilage, which pushes the sternum inward toward the spine. The structural integrity of cartilage relies on connective tissue proteins like collagen and elastin. Histological studies of costal cartilage removed from patients with pectus excavatum have revealed abnormalities, including disturbances in collagen synthesis. These defects result in cartilage that is overly flexible or has reduced biomechanical stability.
Pectus Excavatum as a Symptom of Syndrome
In a significant subset of cases, pectus excavatum is not an isolated finding but a physical manifestation of a broader, well-defined genetic syndrome. These syndromic forms of the condition involve specific mutations that affect connective tissue throughout the body. Recognizing this distinction is important because the underlying syndrome often carries implications for other organ systems, particularly the heart and blood vessels. High-profile examples include Marfan Syndrome and Ehlers-Danlos Syndrome (EDS), both systemic connective tissue disorders. Pectus excavatum is seen in roughly half of all individuals with Marfan Syndrome. Other associated conditions include:
- Noonan Syndrome
- Loeys-Dietz syndrome
- Poland Syndrome
The presence of a sunken chest, combined with other features like unusual joint flexibility or heart valve problems, can serve as the first clue that a systemic connective tissue disorder is present.
Clinical Evaluation and Severity
Given the potential for genetic and systemic links, a thorough clinical evaluation is required for anyone presenting with pectus excavatum. The initial assessment involves a physical examination to characterize the depth and symmetry of the sternal indentation, as external appearance can sometimes underestimate the internal severity. To objectively measure the degree of the deformity and its potential impact on internal organs, a computed tomography (CT) scan is the standard imaging procedure. The CT scan allows for the calculation of the Haller Index (HI), which is the ratio of the maximum internal transverse chest diameter to the shortest anteroposterior distance between the sternum and the spine. An index of 3.25 or greater is generally considered severe and often triggers a discussion about corrective measures. The evaluation also includes functional testing, such as echocardiography to assess for cardiac compression and pulmonary function tests to determine if lung capacity is restricted.