The term intron was introduced by American biochemist Walter Gilbert:
"The notion of the cistron [i.e., gene] ... must be replaced by that of a transcription unit containing regions which will be lost from the mature messenger – which I suggest we call introns (for intragenic regions) – alternating with regions which will be expressed – exons." (Gilbert 1978)
The term intron also refers to intracistron, i.e., an additional piece of DNA that arises within a cistron.Although introns are sometimes called intervening sequences, the term "intervening sequence" can refer to any of several families of internal nucleic acid sequences that are not present in the final gene product, including inteins, untranslated regions (UTR), and nucleotides removed by RNA editing, in addition to introns. Distribution
The frequency of introns within different genomes is observed to vary widely across the spectrum of biological organisms. For example, introns are extremely common within the nuclear genome of jawed vertebrates (e.g. humans and mice), where protein-coding genes almost always contain multiple introns, while introns are rare within the nuclear genes of some eukaryotic microorganisms, for example bakers/brewers yeast (Saccharomyces cerevisiae). In contrast, the mitochondrial genomes of vertebrates are entirely devoid of introns, while those of eukaryotic microorganisms may contain many introns. A particularly extreme case is the Drosophila dhc7 gene containing a ≥3.6 megabase (Mb) intron, which takes roughly three days to transcribe. On the other extreme, a 2015 study suggests that the shortest known metazoan intron length is 30 base pairs (bp) belonging to the human MST1L gene.
Transient neonatal pustular melanosis (TNPM), also known as pustular melanosis, is a transient rash common in newborns. It is vesiculopustular and made up of 1–3 mm fluid-filled lesions that rupture, leaving behind a collarette of scale and a brown macule. [3] This rash occurs only in the newborn stage, usually appearing a few days after birth[2], but is sometimes already present at birth[3]. The rash usually fades over three to four weeks  but may linger for up to three months after birth. [3] It can occur anywhere on the body, including the palms and soles. [1][2][3]The cause of TNPM is unknown. No treatment is needed except for parental reassurance. Causes
The cause of TNPM is unknown but it is a common rash in newborns. [3]

Histopathology
Gram, Wright, or Giemsa staining of the pustular contents will show polymorphic neutrophils and occasional eosinophils. [2][3] On histopathology, the pigmented macules will show basal and supra-basal increase in pigmentation without any pigmentary incontinence. [3] Bacterial culture will be negative. [4]It has been suggested that TNPM is merely a precocious form of erythema toxicum neonatorum based on the similar histopathology. [4]

Diagnosis
Transient neonatal pustular melanosis is diagnosed clinically, based on appearance alone, with no need for special testing. Proper identification is important to distinguish it from other serious, infectious neonatal diseases[3] and to help avoid unnecessary diagnostic testing and treatments. Treatment
No treatment is needed except for parental reassurance. The rash spontaneously resolves, usually in three to four weeks,  but may linger for up to three months after birth.