A man suffers from a series of debilitating symptoms; doctors cannot diagnose his illness, but thanks to a chance meeting this mystery will be solved; a woman undergoes a risky left temporal craniotomy.

A teenager is rushed to the hospital after taking aspirin to help alleviate altitude sickness; a woman has pain in her arm that mysteriously spreads.

A woman and her husband decide to start a family after numerous negative pregnancy tests; a man appears to suffer an embolism

A three-year-old's unexplained vaginal bleeding sends her parents searching for answers to help their baby girl. Also, a student plagued by cramps is unable to hold her food down.

A 12-year-old girl experiences abdominal pains and severe headaches until she is diagnosed with a retroflexed odontoid and Chiari One malformation; a firefighter and paramedic is diagnosed with acquired immunodeficiency syndrome (AIDS).

A 3-month-old boy has breathing difficulties; a woman has stomach problems; stepping on a crochet hook causes strange problems for a patient.

A mother rushes her toddler to hospital when she loses the ability to walk or stand. Plus, a runner tries to sleep off a numbness in his foot, but finds the sensation spreading.

Since birth, Ricky is plagued by respiratory infections and a bizarre inability to grow. Noel is a healthy, active man until mysterious spasms start taking over his life.

Harry's body starts to undergo a mysterious transformation. Sadie finds herself on the brink of starvation after her doctor dismisses her complaints.

Brenda and Jake are delighted when their daughter Isabel is born, but their euphoria quickly turns to panic when Isabel stops eating and her skin turns grey. Noah and Alexis were healthy twins until they suddenly lost all their milestones. Charlie, an active pastor, has difficulty reading; doctors must act quickly to save his eyesight.

When Kylie is born struggling to breathe, doctors aren't sure whether they will find a cure. Also, athlete Michael is left fighting for his life when a sore throat turns deadly.

An 18-month-old baby suddenly starts screaming one afternoon in the pool, and begins exhibiting extremely painful symptoms when exposed to sunlight, with porphyria later found to be the culprit. A mother of two children begins to suffer a series of very debilitating headaches.

Diane finds two small, red bumps on her foot; within hours her foot is swollen and appears black and blue; despite undergoing tests, the medical team has no diagnosis.

After blisters appear all over the body of young Julie McCawley, she appears to have Stevens-Johnson syndrome; Conor Heybach's weight gain and uncontrollable appetite is a mystery until a doctor discovers he has Prader-Willi syndrome.

After moving houses, and months of strange behavior, 12-year-old Sammy stops walking and only hops; the doctors are the only hope to discover the cause of his bizarre symptoms. He is eventually diagnosed with PANDAS, a condition in which antibodies mistake his brain for Streptococcus bacteria.

After suffering a series of debilitating incidents believed to be the result of Crohn's disease, Karen, an albino, has to have most of her colon removed. Several decades later, at the age of 38, she receives a phone call from someone who suggests she is suffering from a rare and fatal disease, Hermansky-Pudlak syndrome, which is also the cause of her albinism.

A girl sleeps for ten days in a row, but tests are normal and doctors are perplexed; a marathon runner experiences unexplainable fatigue.

June has a biopsy and, when a mark appears on the site, she has surgery, leaving her with a growing open wound. Her doctor diagnoses her with a flesh eating virus. Can June's life be saved?

When Jeanne fails to hit puberty, doctors discover that something truly bizarre is the cause; analysis of her DNA finds that she is genetically male, possessing Y chromosomes, but due to the rare genetic disorder Swyer syndrome, she appears outwardly female. Mary is stricken with a collapsed lung and breathing problems.

A baby who cries and holds her cheek; a woman who gained 100 pounds in three months and developed severe acne; and an avid athlete struggling to catch his breath. Featuring trigeminal neuralgia, polycystic ovary syndrome and alpha-1 antitrypsin deficiency.

A woman starts failing after a family vacation; another woman, who has suffered from stomach pains for years, has problems with swelling during menstruation.

Rachele Lacount and Mike West are delighted that their baby has started to walk and talk, but suddenly they realize that something is wrong with his right eye. Since middle school, Cherryl Marshall struggled with taming her obscene body odor.

Parents notice their 7-month-old son has troubling physical impairments, then begins violently harming himself, culminating in a horrifying incident where the child bites off his own lower lip; he is later diagnosed with the genetic condition Lesch-Nyhan syndrome. A woman traveling the world starts experiencing unusual back pain and tingling in her feet that rapidly develops into a spreading paralysis; following the successful use of plasmapheresis, the cause of the dangerous condition is identified as Devic's disease, an inflammation of the spinal cord.

Nicole is a teenager who feels excruciating pain in her jaw and her face starts to sink, with her affliction later found to be the result of Parry-Romberg syndrome. Kevin thinks he has food poisoning, but he starts to lose motor coordination.

Walt has always been in good health until one day he suddenly faints; when he arrives at hospital, his blood pressure is very low and he has gained 100 lb (45 kg) of weight in water. It is eventually discovered that he is suffering from systemic capillary leak syndrome.