Genetics, based on twin studies, appear to play only a small role in astigmatism as of 2007.Genome-wide association studies (GWAS) have been used to investigate the genetic foundation of astigmatism. Although no conclusive result has been shown, various candidates have been identified. In a study conducted in 2011 on various Asian populations, variants in the PDGFRA gene on chromosome 4q12 were identified to be associated with corneal astigmatism. A follow-up study in 2013 on the European population, however, found no variant significantly associated with corneal astigmatism at the genome-wide level (single-nucleotide polymorphism rs7677751 at PDGFRA). Facing the inconsistency, a study by Shah and colleagues in 2018 included both populations with Asian and Northern European ancestry. They successfully replicated the previously identified genome-wide significant locus for corneal astigmatism near the PDGFRA gene, with a further success of identifying three novel candidate genes: CLDN7, ACP2, and TNFAIP8L3. Other GWAS studies also provided inconclusive results: Lopes and colleagues identified a susceptibility locus with lead single nucleotide polymorphism rs3771395 on chromosome 2p13.3 in the VAX2 gene (VAX2 plays an important role in the development of the dorsoventral axis of the eye); Li and associates, however, found no consistent or strong genetic signals for refractive astigmatism while suggesting a possibility of widespread genetic co-susceptibility for spherical and astigmatic refractive errors. They also found that the TOX gene region previously identified for spherical equivalent refractive error was the second most strongly associated region.
In phonetics, denasalization is the loss of nasal airflow in a nasal sound, such as a nasal consonant or a nasal vowel. That may be due to speech pathology but also occurs when the sinuses are blocked from a common cold, when it is called a nasal voice, which is not a linguistic term. Acoustically, it is the "absence of the expected nasal resonance." The symbol in the Extended IPA is ⟨◌͊⟩. When one speaks with a cold, the nasal passages still function as a resonant cavity so a denasalized nasal [m͊] does not sound like a voiced oral stop [b], and a denasalized vowel [a͊] does not sound like an oral vowel [a]. However, there are cases of historical or allophonic denasalization that have produced oral stops. In some languages with nasal vowels, such as Paicĩ, nasal consonants may occur only before nasal vowels; before oral vowels, prenasalized stops are found. That allophonic variation is likely to be from a historical process of partial denasalization. Similarly, several languages around Puget Sound underwent a process of denasalization about 100 years ago. Except in special speech registers, such as baby talk, the nasals [m, n] became the voiced stops [b, d]. It appears from historical records that there was an intermediate stage in which the stops were prenasalized stops [ᵐb, ⁿd] or poststopped nasals [mᵇ, nᵈ]. Something similar has occurred with word-initial nasals in Korean; in some contexts, /m/, /n/ are denasalized to [b, d].