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Rhabdomyolysis is a life-threatening condition that involves muscle cell destruction. Among its etiologies, severe hyper-natremia is a less common cause. We report a teenage girl with congenital central hypoventilation syndrome and hypothalamus dysfunction syndrome who presented with extreme hypernatremia (sodium, 211 mmol/L) with rhabdomyolysis (creatine kinase, 32,850 U/L) and acute renal failure (creatinine, 6.1 mg/dL) following gastroenteritis with 7-kg weight loss. Rhabdomyolysis subsequently led to acute renal failure and hyperkalemia. Acute hemodialysis was initiated on hospital day 3 for hyperkalemia. This resulted in a 13 mmol/L fall in serum sodium in 3 hours despite using a 156 mmol/L sodium bath, but without the development of cerebral edema or neurological defect. This report highlights an unusual cause of rhabdomyolysis in children and the experience of managing such a difficult clinical situation. [J Chin Med Assoc 2009;72(10):555–558]

A unique class of proteins, containing high-mobility group (HMG) domain(s), recognizes unusual DNA structures and/or bends specific to AT-rich linear double-stranded DNA. The DNA binding feature of these proteins is exhibited in the HMG domain(s). Although the sequence specific and non-sequence specific HMG domains exhibit very high degrees of sequence similarity, the reasons for the difference between their DNA recognition mechanisms are unclear. A series of zebra fish SOX9 HMG domain mutants was prepared in an effort to elucidate the importance of various residues on protein stability and DNA binding. This study is the first of a comprehensive mutagenesis study on a sequence specific HMG domain. Comparing how various residues influence sequence specific and non-sequence specific HMG domains helps us to rationalize their mode of action. Positively charged amino acids concentrated at the surface of sequence specific HMG domains recognize specific, linear AT-rich DNA segments. After the negative charges at the surface of the DNA are neutralized, the hydrophobic residues of the protein may intercalate DNA. Phenylalanine at position 12 plays a crucial role in the sequence specific HMG domain. The differences in pI values, the instability index, and DNA contact regions between sequence and non-sequence specific HMG domains are associated with their functional modes.