What is pleurisy and how is pleurisy related to the pleura in the lungs?
Pleurisy is also known as pleuritis which is the inflammation of the pleural.
  The smooth movement of the parietal pleural over the visceral pleural is during inspiration and expiration is impaired or obstructed when the pleural surfaces become damaged and roughened particularly due to bacterial infections. This produces the symptom called pleurisy, a severe stabbing feeling on the chest wall during inspiration and expiration.

  Damage to the pleural linings may result in fibrous scar formation leading to the inability of the two pleura to slide over one another in a proper manner.

The result of this is that some of the lymphatics draining the lungs and its pleura deposit their content in the fibrous septa formed in between the pleura. These lymphatics can also dislodge large quantities of fluid into the pleural cavity leading to pleural effusion.
Unfortunately,these lymphatics can also carry with them bacteria and tumour cells into the pleural cavity thereby producing infected pleural effusion and malignant pleural effusion respectively.

Mesothelium is a kind of cancer that mostly affects mesothelium(epithelium of the serous body cavities) of the body. Mesothelioma is a dangerous cancerous disease of the mesothelium.
Although it can affect other body cavities like the the peritoneal cavity,pericardial cavity and tunica vaginalis of the testis(testicular mesothelioma) but the most common forms of mesothelioma usually affect the lung pleura.
 It is believed to be caused by the inhalation of asbestos fibre. This is the only known form of pleural cancer in the body.

Most people who develop mesothelioma have worked in jobs where they inhaled asbestos, or were exposed to asbestos dust and fibers in other ways. It has also been suggested that washing clothes of a family member who worked with asbestos increases their risk for developing mesothelioma.
It should also be noted that cigarette smoking also increases the rate off developing mesothelioma in the lungs.
 Signs and symptoms of mesothelioma include shortness of breath due to pleural effusion (fluid between the lung and the chest wall) or chest wall pain, and constitutional signs such as unexplained weight loss.

Presently,there is no cure for mesothelioma except for treatments like surgery and chemotherapy which have helped to reduce the incidence of the disease.

Down syndrome is a hereditary and congenital disease usually associated with Trisomy 21.
Children with the disease usually show the foolowing characteristics:
1)Extensive mental retardation
2)Craniofacial Abnormalities
3)Small ears
4)Flat faces
5)Cardiac defects
6)Hypotonia(low muscle tone)
7) Folds of skin on the medial side of the eyes
  These individual also show signs of thyroid dysfunction,high levels of leukemia and also premature aging.
 Down syndrome is usually caused by trisomy 21 where an additional chromosome is added to the normal number of chromosomes at chromosome number 21.(Remember that trisomy 21 is a type of aneuploidy,a chromosomal abnormality). Trisomy 21 is caused by meiotic non disjunction during fertilization.
    Down syndrome is usually noticed in children born by women 35 years of age and above.The prevalence of the disease in younger women is rare,about 1 in 2000 live births.