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Parkinson's is a result of the loss of cells in various parts of the brain, including one portion that produces the neurotransmitter dopamine. Dopamine is essential for being able to move in a coordinated way, so the loss of dopamine causes the tremors often associated with the condition. While the exact cause of Parkinson's is unknown, genetics and environment are contributing factors. Most cases occur in patients with no family history of Parkinson's disease, but there are 13 gene mutations that have been linked to either causing the disease or increasing one's risk of developing it. Certainly not everyone who carries these gene mutations develops Parkinson's, but identifying these genetic indicators is the beginning of developing more precise treatments.

Since this time, research has focused on biological factors that may lead to autistic behaviours. This has found very clearly there is no one cause of autism. A variety of genetic factors are likely to be the ultimate cause of most cases of autism. These may work by themselves, or in combination with environmental factors, to lead a child's brain to develop differently and result in autistic behaviours.

Until very recently it was thought that just one bacterium was to blame for causing Lyme disease in humans. But it turns out that a second, related bug can cause it too.

This interrupted case is based on a genome wide association study (GWAS) that identified the genetic variation causing some inhabitants of the Solomon Islands to have blond hair. The case illustrates the connection between genotype and phenotype, and an application of Hardy-Weinberg equilibrium. The narrative focusses on John and his new roommate, Peter, from the Solomon Islands who happens to have dark skin and blond hair. Using thought-provoking questions students learn about the genetics and the biochemistry of the hair color trait and how a single genetic variation can influence phenotype. Is migration or mutation involved?  Upon completion of the activity students will know the source of the genetic variation that causes the blond hair phenomenon in the Solomon Islands and if it has any European origins. The case was written for an upper-level genetics course, but could also be adapted for introductory biology or for a genetics course for non-majors. An optional PowerPoint presentation with clicker questions is available for download from within the Answer Key.

In the largest study of its kind, a research team has meshed extensive genome data on more than 50,000 people with their electronic health records and identified potential new disease-causing genes. The data further suggest that about one in 250 people may harbor a gene variant that puts them at risk for heart attacks and strokes, yet aren't receiving adequate treatment.

A deadly disease known as African sleeping sickness has puzzled doctors for decades. It would disappear from villages without a trace, only to re-emerge weeks or months later with no known cause. Frustrated health officials wondered how sleeping sickness could persist when not a single villager or animal-the disease's only carriers-tested positive for the insect-borne parasite that causes it. Now, scientists may have an answer at last: They've discovered the disease was hiding in plain sight this whole time, living in and even transmitting via human skin.

This interrupted case study introduces basic modeling to investigate a decline in an American marten population on an island in Southeast Alaska. Two summer field technicians working on a long-term field ecology project for one of their professors notice that there are fewer marten captures this year. Through discussions with their professor, conversations with a local fur trapper, and based on their own observations, they develop a plan to model the population and the potential causes of the decline to solve the mystery. Students use Excel or other database software along with life tables and introductory population ecology to investigate three potential causes of the marten population decline. This case was developed for use in an environmental science or wildlife management course but could also be used in an advanced science high school course or general ecology course. It would be beneficial for students to have some background in statistics including how to interpret R-squared values, p-values, and 95% confidence intervals.

"I Heart Running" is a case study in which students diagnose the cause of exercise-induced tachycardia in an otherwise healthy, 27-year-old female. The patient, Sam, is a long-distance runner and realizes that her exercising heart rate reaches over 200 beats per minute. As the story of Sam's encounters with her physician develops, students are given results from multiple laboratory tests and detailed patient background information.  Students are guided through the material with a series of questions with the ultimate goal of determining the cause of the exercise-induced tachycardia that Sam experiences. The case study is based on actual laboratory results and was designed for students in an upper-level undergraduate Human Physiology course. In this activity students will learn about heart rate, cardiovascular physiology, and oxygen carrying capacity, and factors which influence these concepts, as they try to diagnose Sam.

Iona Twaddell looks at the science of the waterborne disease cholera There are an estimated 3-5 million cases of cholera, a disease caused by the bacterium Vibrio cholera, each year. It is passed on through drinking water that has been contaminated with faeces from someone infected with the bacteria. Cholera causes vomiting and diarrhoea, leading to severe dehydration.

Huntington disease is caused by a mutation in the HTT gene. Understanding how the mutation causes neurodegeneration might help researchers develop treatments that protect brain function. This animation describes the genetic defect that underlies Huntington disease. Created by the editors at Nature Reviews Disease Primers.

4:17 video Think of the ozone layer as Earth's sunglasses, protecting life on the surface from the harmful glare of the sun's strongest ultraviolet rays, which can cause skin cancer and other maladies. Ozone stinks. People who breathe it gag as their lungs burn. The EPA classifies ground-level ozone as air pollution. Yet without it, life on Earth would be impossible. A fragile layer of ozone 25 km above Earth's surface is all that stands between us and some of the harshest UV rays from the sun. The ozone molecule O3 blocks radiation which would otherwise burn skin and cause cancer. On Mars, which has no ozone layer to protect it, solar UV rays strafe the surface with deadly effect, leaving the apparently lifeless planet without the simplest of organic molecules in the upper millimeters of exposed Martian soil.

This case study presents the fictional tale of two neighboring towns that have recently experienced a growth boom and are now suffering the environmental consequences. The case provides an opportunity to explore a wide variety of anthropogenic causes of natural capital degradation. Students are assigned the role of scientists working for the regional Department of Environmental Resources Management, and it is their job to discover the underlying causes for a wide variety of citizen complaints and to suggest reasonable and cost effective solutions. The case may be assigned as a recap activity after teaching a unit on natural capital degradation. The case includes a PowerPoint presentation as well as three lab activities that are included in the teaching notes. The case would be appropriate for high school or lower level undergraduate ecology or environmental science courses.

Technical details aside, Crispr-Cas9 makes it easy, cheap, and fast to move genes around-any genes, in any living thing, from bacteria to people. "These are monumental moments in the history of biomedical research," Baltimore says. "They don't happen every day." Using the three-year-old technique, researchers have already reversed mutations that cause blindness, stopped cancer cells from multiplying, and made cells impervious to the virus that causes AIDS. Agronomists have rendered wheat invulnerable to killer fungi like powdery mildew, hinting at engineered staple crops that can feed a population of 9 billion on an ever-warmer planet. Bioengineers have used Crispr to alter the DNA of yeast so that it consumes plant matter and excretes ethanol, promising an end to reliance on petrochemicals. Startups devoted to Crispr have launched. International pharmaceutical and agricultural companies have spun up Crispr R&D. Two of the most powerful universities in the US are engaged in a vicious war over the basic patent.

Medical researchers have discovered a gene that increases the risk of schizophrenia, a mental illness that affects more than 2 million Americans, sometimes causing delusions and hallucinations. The finding was first reported this week in the scientific journal "Nature".

Most colon cancers may be caused by infections with bacteria that are normally found in cows. For decades we have known that Streptococcus gallolyticus gallolyticus (SGG) is sometimes found in colon tumours, but now the microbes have been found to directly cause tumour growth in mice.

This clicker case was designed to teach students about basic enzyme structure, mechanisms of enzyme inhibition, and mechanisms of drug resistance. The story follows Oliver Casey, a patient afflicted with Chronic Myelogenous Leukemia (CML). CML is caused by a chromosomal mutation that affects the tyrosine kinase ABL, an enzyme important in regulating cell growth and proliferation. The chromosomal mutation gives rise to the BCR-ABL fusion gene that produces a constitutively active ABL kinase, which causes the leukemia. In May 2001, the Food and Drug Administration approved the use of a rationally designed tyrosine kinase inhibitor, imatinib (Gleevec®), for the treatment of CML. During that same month, Gleevec made the cover of TIME magazine, described as "new ammunition in the war on cancer." The case is structured for a flipped classroom environment in which students view preparatory videos (including one by the author) on their own before beginning the case. Written for a first-year introductory biology course, the case could also be adapted for AP/Honors high school biology or a cancer biology course.

Hilary Brown is a PhD student, working in the infection genomics group at the Wellcome Trust Sanger Institute. In this film he describes how to work safely in the lab with bacteria from the human gut including culturing them on agar plates and extracting the DNA for genome sequencing. The infection genomics programme uses a variety of different research approaches to study the biology and evolution of disease-causing organisms such as viruses, bacteria and parasites and understand how they cause disease in humans and other animals.

The activity begins with students observing different organisms or phenomena and developing questions based on their observations. They then sort their questions into those that can and cannot be answered using the methods of science. Students practice writing scientific questions, designing experiments to address scientific questions, developing questions that involve cause and effect, and understanding the importance of cause and effect questions in scientific research. At the end of the activity, students determine the research questions being asked from reading journal article titles and parts of a published paper or other reported results. Several possible extension activities are provided for continuing the investigation and research of phenomena.

This directed case study examines the molecular basis of cystic fibrosis to emphasize the relationship between the genetic code stored in a DNA sequence and the encoded protein's structure and function. Cystic fibrosis is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) protein that functions to help maintain salt and water balance along the surface of the lung and gastrointestinal tract. This case introduces students to "Maggie," who has just been diagnosed with cystic fibrosis. The students must identify the mutation causing Maggie's disease by transcribing and translating a portion of the wildtype and mutated CFTR gene. Students then compare the three-dimensional structures of the resulting proteins to better understand the effect a single amino acid mutation can have on the overall shape of a protein. Students also review the concepts of tonicity and osmosis to examine how the defective CFTR protein leads to an increase in the viscosity of mucus in cystic fibrosis patients. This case was developed for use in an introductory college-level biology course but could also be adapted for use in an upper-level cell or molecular biology course.

Michael Mosley looks into the dangerous ingredients added to processed meat that becomes a suspect in causing cancer.