On an educational trip to Uttaranchal,Ketki and her friends observe that many local people have swollen necks. Please help Ketki and her friends to find out the solutions to the following questions.
$(a)$ Which probable disease are these people suffering from?
$(b)$ How is it caused?
$(c)$ What effect does this condition have on pregnancy?

(A) These people are likely suffering from goitre,which is characterized by a swollen neck.
$(b)$ Goitre is caused by a deficiency of iodine in the diet. Iodine is essential for the synthesis of thyroid hormones,$T_{3}$ (triiodothyronine) and $T_{4}$ (thyroxine). When iodine levels are low,the thyroid gland enlarges in an attempt to produce more hormones,leading to hypothyroidism.
$(c)$ During pregnancy,maternal hypothyroidism can severely affect the developing foetus. It may lead to cretinism,which is characterized by stunted growth,mental retardation,low intelligence quotient,abnormal skin,and deaf-mutism.