It is carried by the bacteriophage T12 which integrates into the streptococcal genome from where the toxin is transcribed. The phage itself integrates into a serine tRNA gene on the chromosome.The T12 virus itself has not been placed into a taxon by the International Committee on Taxonomy of Viruses. It has a double-stranded DNA genome and on morphological grounds appears to be a member of the Siphoviridae.The speA gene was cloned and sequenced in 1986. It is 753 base pairs in length and encodes a 29.244 kiloDalton (kDa) protein. The protein contains a putative 30-
amino-acid signal peptide; removal of the signal sequence gives a predicted molecular weight of 25.787 kDa for the secreted protein. Both a promoter and a ribosome binding site (Shine-Dalgarno sequence) are present upstream of the gene. A transcriptional terminator is located 69 bases downstream from the translational termination codon. The carboxy terminal portion of the protein exhibits extensive homology with the carboxy terminus of Staphylococcus aureus enterotoxins B and C1.Streptococcal phages other than T12 may also carry the speA gene. Diagnosis
Although the presentation of scarlet fever can be clinically diagnosed, further testing may be required to distinguish it from other illnesses. Also, history of a recent exposure to someone with strep throat can be useful in diagnosis. There are two methods used to confirm suspicion of scarlet fever; rapid antigen detection test and throat culture.The rapid antigen detection test is a very specific test but not very sensitive.
It is imperative that the correct diagnosis is made the misdiagnosis of a neurofibroma may lead to unnecessary further investigation into associated systemic syndromes such as neurofibromatosis type 1 or multiple endocrine neoplasia syndrome.The differential diagnosis for PEN includes a neurofibroma, basal cell carcinoma, melanocytic nevus, epidermoid cyst and a skin appendage. Treatment
The only definitive treatment of PEN is surgical excision. Excision is curative and rarely recur. Gallery
See also
List of cutaneous conditions

References


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