Severe Combined Immunodeficiency (SCIDs) - Essay Example

Severe Combined Immunodeficiency Severe Combined Immunodeficiency (SCID) is a severe immunodeficiency genetic disorder. It is characterized by complete inability of the immune system to mount, coordinate, and sustain an appropriate immune response. This condition occurs due to absent or atypical T and B lymphocytes. There are several forms of SCID which occur in animal species. SCID in horse is autosomal recessive disorder that affects the Arabian horse. The affected foal is born with no immune system.

The animal develops opportunistic infection and succumbs to these infections, usually within the first four to six months of life. The most common infections are respiratory infections. Since the disease is a recessive trait, a horse carrying one of the genes appears normal but when a foal is born with two defective genes the result is 100% fatal (Oglesby, horseadvice.com). Heterogenous carriers can transfer mutations to their offspring. The condition is characterized by lymphopenia, hypogammaglobulinemia, and absence of tissue lymphocytes.

There is a definitive test for SCID gene in Arabian foals. The test is performed on secretions from the mucosal swab or blood. The specific test involves cutting up the DNA with PCR restriction enzymes and then examining the relevant section of the gene. Genetic cause of a SCID is a 5-base pair deletion within the catalytic subunit of DNA dependent pro-tein kinase (DNA-PKc) (Zavrtanik, Mesaric, & Majdic, 2005, p.37-41). This mutation causes a frame shift at codon 3155 of the transcript.

This further results in 967 amino acid deletion from the C- terminus that includes entire phosphatidylinositol 3- linase domain, thus making DNA-PKC functionally inactive. The affected foals are clinically normal at birth. But they soon develop signs of infection during the first 2 months of life. The first clinical signs are usually noticed between two days and six weeks of age. These signs include fever, tachycardia and tachypnea. The small animals are unthrifty, lethargic and tire easily.

But they continue to nurse and eat solid food. Respiratory infection occurs commonly and is manifests as bilateral nasal discharge, cough and dyspnea. Those who survive longer may develop chronic diarrhoea, alopecia and dermatitis (Zavrtanik, Mesaric, & Majdic, 2005, p.37-41). The most constant findings in SCID are lymphopenia (