Marfan Syndrome: The combination of tall stature, long limbs, pectus excavatum, abnormally long fingers (arachnodactyly), and hypermobility are all classic features of Marfan syndrome. Although the absence of a family history does not rule out the diagnosis, as it can result from a de novo mutation.

Homocystinuria: This condition can mimic Marfan syndrome with similar skeletal features such as tall stature, long limbs, and arachnodactyly, but it is also associated with intellectual disability, seizures, and thromboembolic events.
Ehlers-Danlos Syndrome: Characterized by hypermobile joints, skin hyperextensibility, and tissue fragility. While it shares some features with Marfan syndrome, such as joint hypermobility, it lacks the distinctive skeletal and ocular findings.
Loeys-Dietz Syndrome: Features include tall stature, arachnodactyly, and hypermobility, similar to Marfan syndrome, but it is distinguished by the presence of widespread arterial aneurysms and tortuosity.

Aortic Aneurysm or Dissection: Regardless of the underlying diagnosis, the presence of features suggestive of Marfan syndrome necessitates screening for aortic root dilatation due to the high risk of aortic aneurysm or dissection, which can be fatal if not identified and managed promptly.
Pulmonary Embolism: In conditions with increased risk of thromboembolic events, such as homocystinuria, pulmonary embolism is a potentially life-threatening complication that must be considered.

Stickler Syndrome: A genetic disorder characterized by distinctive facial features, eye abnormalities, hearing loss, and joint hypermobility. While it shares some features with Marfan syndrome, its overall clinical picture is distinct.
Beals Syndrome (Congenital Contractural Arachnodactyly): Characterized by arachnodactyly, contractures, and ear abnormalities. It lacks the significant ocular and cardiovascular features of Marfan syndrome but can be considered in the differential diagnosis based on skeletal features.