Case Study Theory Index

PRECONCEPTION

1. Heather & Ian.

PREGNANCY & PERINATAL PERIOD

1. Tom & Louise.

2. Emily.

3. Sivia

4. Mara

2. Chloe.

INFANCY

1. Joe.

2. Chloe.

3. Ellie.

CHILDHOOD & ADOLESCENCE

1. Jasmine.

2. Janie.

3. James.

Brief Description	Retinitis Pigmentosa (RP) is the name given to a group of inherited eye diseases that affect the retina. The retina lines the interior surface of the back of the eye and is made up of several layers. One layer contains two types of photoreceptor cells referred to as rods and cones. Cones are responsible for sharp, central vision and colour vision and are primarily located in a small area of the retina called the fovea. The area surrounding the fovea contains the rods, which are necessary for peripheral vision and night vision. The number of rods increases towards the periphery of the retina. Rod and cone photoreceptors convert light into electrical impulses and send the message to the brain via the optic nerve. In RP, the photoreceptors (primarily the rods) begin to deteriorate and lose their ability to function. As rods are primarily affected, it becomes harder to see in dim light, thus causing a loss of night vision. Gradually, the condition worsens and peripheral vision disappears, which results in tunnel vision. The ability to see colour is eventually lost too and in the late stages of the disease, there is only a small area of central vision remaining. Ultimately, this is lost resulting in blindness. Cells from the pigmented layer of the retina also migrate into the nerve cell containing layer; causing a typical pattern of black or brown star shapes in the retina that give the disease its name.
Genetic Background	Retinitis Pigmentosa can be classified according to its inheritance pattern. The different forms of RP result from the presence of one or two abnormal genes. There are three possible inheritance patterns, autosomal dominant, autosomal recessive and X-linked. James’ family in this particular case study have an autosomal dominant form of RP. Autosomal dominant RP (AdRP) occurs in about 15-25% of affected individuals and at least 12 different genes have been identified as causing AdRP. People with AdRP will usually have an affected parent and the risk for affected siblings or children is 50%.
Incidence/Prevalence	UK incidence = 1 in 3,500 live births
Related Biology Links	The Human Eye Anatomy of the Retina
Support Groups	British Retinitis Pigmentosa Society Retina International
Other Information Sources	OMIM Reference for many RP genes Retinitis pigmentosa overview Genetics and Retinitis Pigmentosa Retinitis pigmentosa
GeneSense Theory
	Go back to James

 

ADULT 1

1. Bob & Carol.

2. Cathy.

Brief Description	Breast cancer is the most common type of cancer amongst women. Each breast has 15- 20 sections (lobes), each of which has many smaller sections (lobules). The lobes and lobules are connected by thin tubes (ducts). The most common type of breast cancer starts in the ducts (ductal cancer); although other types include cancer beginning in the lobes or lobules (lobular carcinoma) and a less common Inflammatory breast cancer. The average woman, without an inherited breast cancer gene abnormality, has about 11% risk of developing breast cancer over a 80-year life span. However, some women inherit an abnormal gene eg. BRCA1 or BRCA2, which confers an 85% risk of developing breast cancer by age 70. Women with BRCA1 and BRCA2 abnormalities are also at increased risk of developing ovarian cancer. Yet despite the increased risk, not every person with an inherited BRCA1 or BRCA2 abnormality develops cancer. The risks associated with BRCA1 and BRCA2 mutations may be affected by: 1. Lifestyle and environmental factors 2. How well other genes work with BRCA1 and BRCA2 to protect the body against cancer 3. The particular mutation in BRCA1 or BRCA2 and how it affects the proteins that are supposed to suppress cancer. Many people believe that cancers caused by inherited genetic abnormalities are more aggressive than other cancers. However, recent evidence suggests that a woman with an abnormal gene who develops breast or ovarian cancer may have a less aggressive form of the disease than women without an abnormal gene.
Genetic Background	Specific breast cancer gene mutations eg. BRCA1 (on chromosome 17) and BRCA2 (on chromosome 13) only account for 5-10% of all breast cancer cases diagnosed. They are autosomal dominant mutations and if a parent has this gene, then any offspring will have a 50% risk of inheriting the same gene. The majority of breast cancers diagnosed are caused by sporadic events. Risk of breast cancer increases with age and it is most common after the age of 50; although lifestyle, reproductive history and environmental factors also play a significant role in the development of breast cancer.
Incidence/Prevalence	UK = 1 in 9 women (between the ages of 20 and 80) will develop a non-hereditary form of breast cancer.
Related Biology Links	Proto-oncogenes and Cancer Tumour Suppressor Genes
Support Groups	Breast Cancer Care, UK Cancer BACUP Cancer Research, UK
Other Information Sources	OMIM reference: Breast Cancer: Risks and Prevention Human Milk and Lactation
GeneSense Theory
	Go back to Cathy

 

3. Dennis.

Brief Description	Familial adenomatous polyposis (FAP) is a type of Bowel Cancer that affects the lower part of the digestive system: the colon and the rectum. Bowel cancer is the 3rd most common type of cancer in men and the 2nd most common cancer in women, killing around 20,000 people a year in the UK. Polyposis means that lots of polyps, often on stalks like small mushrooms, develop in the bowel. The symptoms of this type of cancer include: 1. Blood or mucus in the stools 2. Lasting change in normal bowel habits (diarrhoea or constipation) 3. Losing weight 4. Pain in the abdomen or rectum 5. Straining feeling in the rectum If the symptoms are found to be caused by cancer, then the majority of individuals will need surgery to remove the diseased segment of the bowel. In many cases the bowel will continue to work as before, with stools passing through the bowel, rectum and anus. However, in some cases, depending on the location and size of the cancer that is removed, the bowel cannot be repaired and a colostomy will be required. A colostomy involves diverting the route of the bowel through a hole in the abdomen, with a bag to collect the faeces.
Genetic Background	Only 5-10% of bowel cancers are believed to be hereditary, i.e. can be linked to a distinct mutation in one of the known bowel cancer genes. Therefore, nine out of ten people with bowel cancer will have the sporadic and not the inherited form of bowel cancer. Families who have a mutation in one of the known bowel cancer genes will have several members with bowel cancer. They will probably have two or more affected relatives with bowel cancer in at least two generations. Three types of inherited bowel cancer are currently known: 1. Familial adenomatous polyposis (FAP). Here, hundreds of benign (not cancerous) polyps are found in the bowel. This happens at a relatively young age (eg. teenagers) and if not treated, some of these polyps will eventually develop into malignant cancer. It is caused by an autosomal dominant mutation to the APC gene on chromosome 5, which triggers tumour formation. This is the cancer outlined in the case study with Dennis. 2. Hereditary non-polyposis colorectal cancer (HNPCC). Here, there are fewer polyps growing in the bowel but there is still a tendency to develop tumours early on in life. HNPCC is also caused by an autosomal dominant mutation to one of several DNA repair genes. 3. A 3rd type of less common but inherited bowel cancer recently identified is MYH associated polyposis (or MAP). Here, a person needs two faulty copies of the gene in question to develop cancer, as the mutation is recessively inherited.
Incidence/Prevalence	UK 'FAP' incidence = 1 in 10,000
Related Biology Links	Proto-oncogenes and Cancer Tumour Suppressor Genes
Support Groups	Cancer UK Cancer BACUP
Other Information Sources	OMIM reference: Bowel Cancer Digestive Disorders FAP Information Gene Reviews
GeneSense Theory
	Go back to Dennis

 

ADULT 2

1. Gordon.

Brief Description	Alzheimer’s disease (AD) is a progressive, neurodegenerative disease. It is characterized in the brain by abnormal protein clumps between neurones (amyloid plaques) and tangled bundles of tau protein fibres inside neurones (neurofibrillary tangles). Age is the most important risk factor for AD; the number of people with the disease doubles every 5 years beyond age 65. Alzheimer's is a form of presenile dementia that is similar to senile dementia, except that it usually starts in the 40s or 50s. AD changes result in neuronal cell death in key regions of the brain, affecting acetylcholine neurotransmission. Symptoms of AD include memory loss, language deterioration, impaired ability to mentally manipulate visual information, poor judgment, confusion, restlessness, and mood swings. After several years, AD destroys cognition, personality and the ability to function; most commonly resulting in death from infection e.g. pneumonia. The early symptoms of AD, which include forgetfulness and loss of concentration, are often missed because they resemble natural signs of aging.
Genetic Background	Several genes have been discovered that cause early onset Alzheimer’s Disease (EOAD) but the condition is not common. Three genes that are inherited in an autosomal dominant fashion are known to cause EOAD. These genes are: 1. Amyloid Precursor Protein (APP) on chromosome 21 This gene codes for a transmembrane protein. 2. Presenilin 1 (PSEN-1) on chromosome 14 This gene codes for a transmembrane protein. It is the most common cause of familial early onset Alzheimer's Disease. 3. Presenilin 2 (PSEN-2) on chromosome 1 This gene codes for a transmembrane protein The amyloid plaques that form in AD patients are derived from APP. This gene is located on chromosome 21 and individuals with trisomy 21 (Down Syndrome) that live to more than age 40 years, invariably have Alzheimer pathology in their brains.
Incidence/Prevalence	Average lifetime risk of Alzheimer’s Disease in UK is 10% but less than 5% of this group will develop EOAD (therefore, 5 people per 1,000 population).
Related Biology Links	Alzheimer’s, Memory & Acetylcholine: Memory and Alzheimer’s Disease:
Support Groups	Alzheimer’s Society, UK: Alzheimer’s Disease International:
Other Information Sources	OMIM reference: Alzheimer’s Disease American Health Assistance Foundation; Medical Illustrations of AD:
GeneSense Theory
	Go back to Gordon

 

2. Eleanor.