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Background: Argininosuccinate lyase (ASL) deficiency is an autosomal recessive urea cycle disorder often presenting with acute encephalomyopathy in the neonatal period. Although ASL is mainly expressed in liver, it is also present in other organs, like the brain. It is unclear whether late onset progressive neuropsychiatric symptoms in certain patients with ASL deficiency are related to long-term exposure to elevated systemic ammonia or to the cerebral deficiency of ASL. Case report: The patient, an 11-year-old girl, developed hyperammonaemic encephalopathy in the neonatal period, leading to the diagnosis of ASL deficiency. Because of insufficient metabolic control with protein restriction, liver transplantation was performed at 3 years, resulting in excellent metabolic control. At age 10 years, she had a first complex partial seizure, reccurring twice in the following 9 months. EEG showed left hemispheric epileptiform activity. MRI showed mild periventricular leukomalacia. MRS showed an elevated ratio of Cho/Cr in white matter, a nonspecific marker of myelin turnover, but no elevation of the Glu/Gln peak. Treatment with lamotrigine resulted in seizure freedom. Conclusions: Although the epilepsy in our patient can be considered a late manifestation of cerebral damage acquired before liver transplantation, neuro-imaging showed only mild white matter changes and no cortical lesions. Alternatively, epilepsy may be related to cerebral deficiency of ASL. MRS showed no arguments for elevated brain ammonia, indicating that brain ASL is not necessary for ammonia detoxification, but may have another function, possibly related to late)onset neurological symptoms. |
