(step1) DiGeorge syndrome 의 기전 운영자 / 2005-09-16 12:17:08
hypocalcemia와 t lymphocyte저하시 DiGeorge syndrome.
This is a 2 month old male with a history of a VSD arriving in the ED for a possible seizure. He has had some cold symptoms since yesterday. This evening, his parents noted an episode of body stiffness, jerking of all extremities, and upward rolling of his eyes lasting one minute. An ambulance was called. His face was described as being blue toward the end of the episode. Paramedics noted him to be breathing spontaneously with no cyanosis. He was transported to the ED. An IV was attempted en route, but this was not successful. No fever was noted in the ambulance. There was no history of fever prior to this episode.
Exam: VS T36.6 (rectal), P132, R60, weight 4.36 kg. He was alert and active. Fontanelle soft and flat. Neck supple. Heart regular, harsh grade III/VI systolic
murmur. Lungs clear. Good color, perfusion, and tone. Shortly after arrival in the ED, another seizure was witnessed. His lower extremities were extended and jerking. No one could recall what his eyes were doing.
DiGeorge syndrome
Pathophysiology: As the name implies, this syndrome is the result of a deletion on the long arm of chromosome 22. The usual deletion is quite long (2-3 Mb), found in 95% of patients with DGA and 75% of patients with VCFS, and defined as the DGCR. This area is believed to have a predilection for such mutations during meiosis as a result of the many repetitive DNA sequences found there. A minimal critical region of 250-500 kb appears to exist within the DGCR and has been identified as DGCR5, which, although it does not transcribe any particular RNA, may function as a regional transcription controller. Support for this theory has come from recent studies of the mouse transcription factor gene Tbx1, which maps to the murine equivalent of the DGCR. Genetically engineered mice have been used to demonstrate that haplo-insufficiency of this gene produces DGA-like cardiovascular abnormalities (but not extracardiac ones).
The result of this deletion is a developmental field defect involving the third and fourth pharyngeal pouches, caused by defective migration of the neural crest cells during the fourth week of embryogenesis. Portions of the heart, head and neck, thymus, and parathyroids derive from these pouches, and the clinical manifestations arise from them as well.
