A 2-month-old girl presents with difficulty breathing and a loud systolic murmur. What is the most likely underlying genetic mechanism?

In this scenario, the 2-month-old girl is experiencing difficulty breathing and has a loud systolic murmur, which suggests a congenital heart defect. Many congenital heart defects can have a genetic basis, and one of the common mechanisms involved in congenital anomalies is deletion.

In genetic terms, a deletion refers to the loss of a segment of DNA, which can result in the absence of one or more genes. This can disrupt normal development processes, leading to structural abnormalities such as those seen in congenital heart disease. For instance, 22q11.2 deletion syndrome, also known as DiGeorge syndrome, can lead to various cardiac anomalies, including tetralogy of Fallot and conotruncal defects, which would explain the symptoms of difficulty breathing and a significant heart murmur in this young patient.

Other genetic mechanisms listed, such as nondisjunction, inversion, and translocation, primarily involve numerical or structural changes in chromosomes that may lead to various genetic syndromes or malignancies, but they are less directly associated with the specific congenital heart defects that would present with the symptoms described in this case. Thus, deletion is the most likely underlying genetic mechanism for the girl’s condition.