USMLE® Step 1 style questions USMLE
A 3-year-old boy is brought to the office for evaluation. He has had recurrent episodes of otitis media and respiratory infections that have required antibiotic treatment. His fine motor skills are within normal limits. He appears unsteady when asked to stand still, but can walk quickly while he plays. He displays nystagmus during finger tracking. Which of the following findings is most likely present in this patient?
By week 4 of development, the embryo takes on a more recognizably “human” form—but to be honest, it still looks more like a shrimp than a baby.
The components of the pharyngeal apparatus develop into various head and neck structures, and sometimes multiple arches join together to give rise to a single structure.
Now, the epithelial tissue of the embryo’s third and fourth pouch turns into the inferior parathyroid glands and superior parathyroid glands, while the epithelial tissue that lines the ventral region of the third pouch forms the thymus.
Both glands then go on to break off from the pharyngeal wall and eventually attach to the posterior side of the thyroid.
On chromosome 22, there’s a gene called TBX1 that controls the development of the 3rd and 4th pharyngeal pouch during the prenatal period.
The parathyroid glands also remains underdeveloped.
The ATM gene encodes a protein whose job is to recognize DNA damage and activate proteins to fix the damage.
- "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
- "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
- "Yen & Jaffe's Reproductive Endocrinology" Saunders W.B. (2018)
- "Bates' Guide to Physical Examination and History Taking" LWW (2016)
- "Robbins Basic Pathology" Elsevier (2017)
- "Survival probability in ataxia telangiectasia" Archives of Disease in Childhood (2005)
- "Molecular genetics of 22q11.2 deletion syndrome" American Journal of Medical Genetics Part A (2018)
- "The Genetics and Epigenetics of 22q11.2 Deletion Syndrome" Frontiers in Genetics (2020)