A B S T R A C TA Galois field GFðp n Þ with p ! 2 a prime number and n ! 1 is a mathematical structure widely used in Cryptography and Error Correcting Codes Theory. In this paper, we propose a novel DNA-based model for arithmetic over GFðp n Þ. Our model has three main advantages over other previously described models. First, it has a flexible implementation in the laboratory that allows the realization arithmetic calculations in parallel for p ! 2, while the tile assembly and the sticker models are limited to p ¼ 2. Second, the proposed model is less prone to error, because it is grounded on conventional Polymerase Chain Reaction (PCR) amplification and gel electrophoresis techniques. Hence, the problems associated to models such as tile-assembly and stickers, that arise when using more complex molecular techniques, such as hybridization and denaturation, are avoided. Third, it is simple to implement and requires 50 ng/μL per DNA double fragment used to develop the calculations, since the only feature of interest is the size of the DNA double strand fragments. The efficiency of our model has execution times of order Oð1Þ and OðnÞ, for the addition and multiplication over GFðp n Þ, respectively. Furthermore, this paper provides one of the few experimental evidences of arithmetic calculations for molecular computing and validates the technical applicability of the proposed model to perform arithmetic operations over GFðp n Þ.

IntroductionCardiac tamponade is a rare manifestation of hypothyroidism, and a less rare cause of pericardial effusion. The accumulation of the pericardial fluid is gradual, and often does not compromise cardiac hemodynamic function. There is a relationship between the severity and chronicity of the disease with the presence of pericardial effusion. There are few cases describing associated pericardial tamponade published in the literature. When a tamponade occurs, a concomitant provocative factor such as a viral pericarditis may be related. Our patient's case appears to be the youngest patient described so far.Case presentationWe report the case of a previously healthy five-year-old Hispanic (non-indigenous) boy who developed rhabdomyolysis with a history of a recent pericardial effusion and tamponade two months before that required the placement of a percutaneous pericardial drainage. Pericardial effusion was considered to be viral. Later on readmission, clinical primary hypothyroidism was diagnosed and thought to be associated with the previous cardiac tamponade. He developed rhabdomyolysis, which was considered to be autoimmune and was treated with steroids. The level of creatine phosphate kinase and creatine kinase MB fraction returned to within the reference rangeone week after our patient was started on steroids and three weeks after he was started on thyroid hormones.ConclusionsPhysicians should consider hypothyroidism as a differential diagnosis in patients with pericardial effusion. Pericardial effusion may progress and cause a cardiac tamponade with hemodynamic instability. The fact that our patient did not have any manifestations of hypothyroidism might have delayed diagnosis.

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