Question: What disease did Mary Stuart, daughter of Frederick II of Denmark, have that eventually cause her death?

Context paragraphs:
Mary Stuart (1605–1607): Mary of England, Scotland and Ireland (8 April 1605 16 September 1607) was the third daughter and sixth child of James VI and I, the first king of a unified England, Scotland and Ireland, by Anne of Denmark, daughter of Frederick II of Denmark and sister of Christian IV of Denmark; her birth was much anticipated.  She developed pneumonia at 17 months and died the following year.

Margaret Stuart (1598–1600): Margaret of Scotland (Margaret Stuart; 24 December 1598 March 1600) was the second daughter of King James VI of Scotland by Anne of Denmark, daughter of Frederick II of Denmark.  Sometime in March 1600, Margaret died of an unknown illness and she was buried in the now ruined Abbey of Holyrood.  Three years later, her father ascended the throne of England.

Cognitive skill: Cognitive functioning is a term referring to an individual’s ability to process to (thoughts) that should not deplete on a large scale in healthy individuals.  It is defined as "the ability of an individual to perform the various mental activities most closely associated with learning and problem solving.  Examples include verbal, spatial, psychomotor, and processing-speed ability."  Cognition mainly refers to things like memory, the ability to learn new information, speech, understanding of written material.  The brain is usually capable of learning new skills in the aforementioned areas, typically in early childhood, and of developing personal thoughts and beliefs about the world.  Old age and disease may affect cognitive function, causing memory loss and trouble thinking of the right words while speaking or writing ("drawing a blank").  Multiple sclerosis (MS), for example, can eventually cause memory loss, an inability to grasp new concepts or information, and depleted verbal fluency.  Not all with the condition will experience this side effect, and most will retain their general intellect and the ability.

Hans Hermann von Katte: Hans Hermann von Katte (28 February 1704 – 6 November 1730) was a Lieutenant of the Prussian Army and the friend of the future King Frederick II of Prussia, who was at the time the Crown Prince.  He was executed by Frederick's father King Frederick William I of Prussia when Frederick II plotted to escape from the Kingdom of Prussia to the Kingdom of Great Britain.  Some believe that Frederick intended to defect to the service of George II of Great Britain (Frederick William's maternal first cousin and Frederick's maternal uncle) and possibly return to Prussia to depose Frederick William.

Frederick of Pettorano: Frederick of Pettorano ("c".  1212/3 – after 1240) was the eldest illegitimate son of Frederick II, king of Sicily and Germany.  He was born on Sicily to an Italo-Norman noblewoman after his father's first marriage to Constance of Aragon.  This mistress's name is unknown, but she came from a family of Norman counts on Sicily and had a relationship with the teenage Frederick between 1211 and 1212.  Their relationship ended when King Frederick went to Germany and in 1213 took up with another woman, a certain Adelaide.  Besides Frederick of Pettorano, Frederick II probably named two other sons after himself: another illegitimate son, Frederick of Antioch, and a legitimate son by his wife Isabella.  This last is known only by the initial "F." and died young.

Henry Frederick, Prince of Wales: Henry Frederick, Prince of Wales (19 February 1594 – 6 November 1612) was the elder son of James VI and I, King of England and Scotland, and his wife, Anne of Denmark.  His name derives from his grandfathers: Henry Stuart, Lord Darnley, and Frederick II of Denmark.  Prince Henry was widely seen as a bright and promising heir to his father's thrones.  However, at the age of 18, he predeceased his father when he died of typhoid fever.  His younger brother Charles succeeded him as heir apparent to the English, Irish and Scottish thrones.

Division of Altenburg: The Division of Altenburg (German: "Altenburger Teilung") was the plan for the division of the Meissen lands agreed upon by the two hostile Wettin brothers Elector Frederick II of Saxony and William III on 16 July 1445 at Altenburg.  The brothers had attempted to reconcile, but eventually the division led the Saxon Fratricidal War (German: "Sächsischer Bruderkrieg"), which began in 1446 and lasted for five years, until the Peace of Naumburg was negotiated in 1451.  Following the peace, the subsequent Treaty of Eger in 1459, and the deaths of Frederick II and Wilhelm III, the two sons of Frederick II eventually gained control of the land of both their father and William III.

Kunz von Kaufungen: Kunz von Kaufungen (also known as Conrad von Kaufungen, or Kunz von Kauffungen; c. 1410 - July 14, 1455), was a German knight and military commander.  A veteran of the Hussite wars, he also fought for Frederick II, Elector of Saxony against Frederick's brother Duke William III during the Saxon Fratricidal War (1446–1451).  Afterwards, Kunz was not repaid or recognized for his services and loss of property during the war, and eventually during the "Prinzenraub" (English: "The stealing of the princes") he kidnapped Frederick II's two sons.  He was caught and later executed.

Coronary artery ectasia: Coronary artery ectasia is a rare disease that occurs in only 0.3-4.9% of people in North America.  Coronary artery ectasia is characterized by the enlargement of a coronary artery to 1.5 times or more than its normal diameter.  The disease is commonly asymptomatic and is normally discovered when performing tests for other conditions such as coronary artery disease, stable angina and other acute coronary syndromes.  Coronary artery ectasia occurs 4 times more frequently in males than in females and in people who have risk factors for heart disease such as smokers.  While the disease is commonly found in patients with atherosclerosis and coronary artery disease, it can occur by itself and in both cases it can cause health problems.  The disease can cause the heart tissue to be deprived of blood and die due to decreased blood flow, and blockages due to blood clots or spasms of the blood vessel.  This blood flow disruption can cause permanent damage to the muscle if the deprivation is prolonged.  Coronary artery ectasia also increases the chance of developing large weak spots in the affected coronary arteries, or aneurysms that can rupture and result in death.  The damage can result in angina which is pain in the chest and is a common complaint in these patients.

Frederick II of Denmark: Frederick II (1 July 1534 – 4 April 1588) was King of Denmark and Norway and duke of Schleswig from 1559 until his death.

Supporting paragraphs: Mary Stuart (1605–1607) Frederick II of Denmark
Answer: pneumonia