Reverse transcription polymerase chain reaction is a laboratory technique combining reverse transcription of RNA into DNA and amplification of specific DNA targets using polymerase chain reaction. It is primarily used to measure the amount of a specific RNA. The main advantage of PCR is its sensitivity: only one strand of sample DNA is needed to detect a particular DNA sequence. It now has many uses including prenatal diagnosis, detection of mutated oncogenes and diagnosis of infections.

Drug metabolism can be broadly classified into:
Phase I (functionalization) reactions: also termed non-synthetic reactions, they include oxidation, reduction, hydrolysis, cyclization and de-cyclization. The most common and vital reactions are oxidation reactions. (Of the given enzymes only Alcohol dehydrogenase is involved in phase I drug metabolism. Succinate dehydrogenase, is a vital enzyme involved in the Kreb’s cycle and the mitochondrial electron transport chain). They are mainly catalysed by Cytochrome P-450 enzyme.

Phase II (conjugation) reactions: occur following phase I reactions, they include reactions: glucuronidation and sulphate conjugation, etc. They are mostly catalysed by UDP-glucuronosyltransferase enzyme. Other phase II enzymes include: sulfotransferases, N-acetyltransferases, glutathione S-transferases and methyltransferases.

Infection of chickenpox in the first half of pregnancy can result in congenital varicella syndrome. It presents as cerebral, cortical and cerebellar hypoplasia with convulsions and rudimentary digits. Prevention is by administering varicella vaccine, even before pregnancy. Varicella immunoglobulin is administered to pregnant women who are exposed to infection. Infection during pregnancy is treated with acyclovir.

T. gondii infection in immunocompetent people is usually asymptomatic. It can present as fits in patients with AIDs, who are immunosuppressed. Additionally, infection in the first trimester of pregnancy is very harmful. Congenital toxoplasmosis presents with intracranial calcifications, classically. It can also present with hydrocephalus, microcephaly, blindness, petechiae. Siramycin is the drug of choice to try to prevent vertical transmission from mother to baby. It is typically gotten from cat faeces or raw/undercooked meat, not raw eggs (raw eggs: think salmonella).

PCR is a simple, yet elegant, enzymatic assay, which allows for the amplification of a specific DNA fragment from a complex pool of DNA. PCR can be performed using source DNA from a variety of tissues and organisms, including peripheral blood, skin, hair, saliva, and microbes. Only trace amounts of DNA are needed for PCR to generate enough copies to be analysed using conventional laboratory methods. For this reason, PCR is a sensitive assay. Each PCR assay requires the presence of template DNA, primers, nucleotides, and DNA polymerase. The DNA polymerase is the key enzyme that links individual nucleotides together to form the PCR product. The above mentioned components are mixed in a test tube or 96-well plate and then placed in a machine that allows repeated cycles of DNA amplification to occur in three basic steps. The machine is essentially a thermal cycler. It has a thermal block with holes, into which the test tubes or plates holding the PCR reaction mixture are inserted. The machine raises and lowers the temperature of the block in discrete, precise and pre-programmed steps. The reaction solution is first heated above the melting point of the two complementary DNA strands of the target DNA, which allows the strands to separate, a process called denaturation. The temperature is then lowered to allow the specific primers to bind to the target DNA segments, a process known as hybridization or annealing. Annealing between primers and the target DNA occurs only if they are complementary in sequence (e.g. A binding to G). The temperature is raised again, at which time the DNA polymerase is able to extend the primers by adding nucleotides to the developing DNA strand. With each repetition of these three steps, the number of copied DNA molecules doubles.

There are two main reasons for using combinations of chemotherapeutic agents rather than single agents. First, different drugs exert their effects through different mechanisms, therefore, carefully combining them will increase the number of tumour cells killed in each cycle as well as decrease their chances of developing drug resistance. Second, there may be an even greater effect with drugs that are synergistic.

The clinical presentation is suggestive of congenital rubella syndrome. The classic triad of presenting symptoms includes sensorineural hearing loss, ocular abnormalities (cataract, infantile glaucoma, and pigmentary retinopathy) and congenital heart disease (patent ductus arteriosus and pulmonary artery stenosis). Other findings in congenital rubella syndrome include CNS abnormalities (mental retardation, behavioural disorders, encephalographic abnormalities, hypotonia, meningoencephalitis, and microcephaly), hepatosplenomegaly, and jaundice.

The patient has spinal cord compression until proven otherwise. Urgent assessment is required.

Spinal cord compression is an oncological emergency and affects up to 5% of cancer patients. Extradural compression accounts for the majority of cases, usually due to vertebral body metastases. One of the most common causes of spinal cord compression is osteoarthritis. It is also more commonly seen in patients with lung, breast, or prostate cancer.

Clinical features include:
1. Back pain: the earliest and most common symptom, may worsen on lying down or coughing
2. Lower limb weakness
3. Sensory changes: sensory loss and numbness
4. Neurological signs: depending on the level of the lesion.
Lesions above L1 usually result in upper motor neurone signs in the legs. Lesions below L1 usually cause lower motor neurone signs in the legs and perianal numbness. Tendon reflexes are increased below the level of the lesion and absent at the level of the lesion.

Management options are:
1. High-dose oral dexamethasone
2. Urgent MRI for consideration of radiotherapy or surgery

Monoclonal gammopathy of undetermined significance (MGUS)—also known as benign paraproteinemia and monoclonal gammopathy—is a pre-malignant condition not necessarily leading to its malignant form—multiple myeloma. MGUS causes increase of a serum monoclonal protein (M protein). It is not associated with ostealgia or increased risk of infections. It is often mistaken for multiple myeloma, differing from the latter in, no immunosuppression, anaemia, hypercalcaemia, lytic bone lesions, or renal failure; normal levels of beta-2 microglobulin; and stable lower levels of paraproteinemia.

Arthritis mutilans is a rare (occurs in only 5% of the patients) and extremely severe form psoriatic arthritis characterized by resorption of bones and the consequent collapse of soft tissue. When this affects the hands, it can cause a phenomenon sometimes referred to as ‘telescoping fingers.’ The associated nail changes are also characteristic of arthritis.