4.04 Systemic Lupus Erythematosus

Rheumatology review for the USMLE Step 1 Exam

• Marfan's syndrome, Ehlers-danlos, and homocystinuria are three distinct diseases that affect connective tissue.
• They share some clinical features like tall stature, long fingers, scoliosis, high arched pallet, chest wall deformities, joint hypermobility, and lens dislocation.
• Marfans is caused by a mutation in the FBN1 gene, resulting in defective fibrillin-1, and the main complication is aortic root dilation.
• Homocystinuria is a metabolic disorder caused by a defect in homocysteine breakdown, leading to elevated levels of homocysteine, and the main complication is thrombosis.
• Ehlers-Danlos is caused by a deficiency in type III collagen, and the main complication is vascular rupture.
• Marfans has an upward lens dislocation, homocystinuria has a downward lens dislocation, and Ehlers-Danlos has hyperextensible skin and joint hyperextensibility.
• Marfans usually presents in teens, homocystinuria in children, and Ehlers-Danlos in young adults.
• Patient presentations: Marfans - scoliosis, long fingers, and caved in chest wall in a tall teen; Homocystinuria - developmental delay, long fingers, and tall stature in a child; Ehlers-Danlos - recurrent bruising, hyper extensible skin, and joint hyperextensibility in a young adult.