Can one get amnesia from canned tuna? What are we forgetting?

The assertion in the Case Report by Roger Ho and colleagues (Jan 24, p 352) that methyl mercury (MeHg) exposure from a daily diet of tuna is responsible for amnesia is problematic toxicologically and clinically. The lowest level reported for adult manifestations of MeHg exposure is 200 μg Hg per L whole blood. That level is used by most national regulatory committees. The blood Hg level of the patient in the Case Report was 28 μg/L. This is equivalent to a hair level of about 5·5 μg/g (ppm). In populations that consume fi sh regularly, this level is commonly seen: one study in the Seychelles found the mean maternal hair level to be 6·9 μg/g. There were no reports of memory loss. Additionally, neurological defi cits from MeHg poisoning are permanent, yet Ho and colleagues’ patient improved. The concomitant reduction of blood Hg by 9 μg/L in 2 months is consistent with the reported 44-day half-time in the blood. In Iraq, the fi rst symptoms of MeHg poisoning were paraesthesias and ataxia. Memory loss has not been a part of clinical reports in the past. Tremor, gingivitis, and erythism are typical of inorganic Hg poisoning. The absence of any of the typical fi ndings of MeHg poisoning, the presence of an atypical fi nding, amnesia, and the patient’s improvement make the conclusion that the patient suff ered from MeHg poisoning from consuming tuna untenable.