H, or h, is the eighth letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is aitch (pronounced , plural aitches), or regionally haitch . History
The original Semitic letter Heth most likely represented the voiceless pharyngeal fricative (ħ). The form of the letter probably stood for a fence or posts. The Greek Eta Η in archaic Greek alphabets, before coming  to represent a long vowel, /ɛː/, still represented a similar sound, the voiceless glottal fricative /h/. In this context, the letter eta is also known as Heta to underline this fact. Thus, in the Old Italic alphabets, the letter Heta of the Euboean alphabet was adopted with its original sound value /h/. While Etruscan and Latin had /h/ as a phoneme, almost all Romance languages lost the sound—Romanian later re-borrowed the /h/ phoneme from its neighbouring Slavic languages, and Spanish developed a secondary /h/ from /f/, before losing it again; various Spanish dialects have developed [h] as an allophone of /s/ or /x/ in most Spanish-speaking countries, and various dialects of Portuguese use it as an allophone of /ʀ/. H is also used in many spelling systems in digraphs and trigraphs, such as ch, which represents /tʃ/ in Spanish, Galician, and Old Portuguese; /ʃ/ in French and modern Portuguese; /k/ in Italian and French. Name in English
For most English speakers, the name for the letter is pronounced as  and spelled "aitch" or occasionally "eitch".
These conditions are relatively uncommon.Conditions where the secondary polycythemia is not caused by physiologic adaptation, and occurs irrespective of body needs include:
Neoplasms – Renal cell carcinoma  or liver tumors, von Hippel-Lindau disease, and endocrine abnormalities including pheochromocytoma and adrenal adenoma with Cushings syndrome. People whose testosterone levels are high because of the use of anabolic steroids, including athletes who abuse steroids, or people on testosterone replacement for hypogonadism or transgender hormone replacement therapy, may develop secondary polycythemia. Blood doping - Secondary polycythemia can be induced by endurance athletes that take erythropoietin-stimulating agents, receive blood transfusions, and take other measures to increase their red blood cell mass in an effort to increase oxygen transport capacity. Altered oxygen sensing
Inherited mutations in three genes which all result in increased stability of hypoxia-inducible factors, leading to increased erythropoietin production, have been shown to cause erythrocytosis:
Chuvash erythrocytosis is an autosomal recessive form of erythrocytosis which is endemic in  patients from the Chuvash Republic in Russia. Chuvash erythrocytosis is associated with homozygosity for a C598T mutation in the von Hippel-Lindau gene (VHL), which is needed for the destruction of hypoxia-inducible factors in the presence of oxygen. Clusters of patients with Chuvash erythrocytosis have been found in other populations, such as on the Italian island of Ischia, located in the Bay of Naples. PHD2 erythrocytosis: Heterozygosity for loss-of-function mutations of the PHD2 gene are associated with autosomal dominant  erythrocytosis and increased hypoxia-inducible factors activity. HIF2α erythrocytosis: Gain-of-function mutations in HIF2α are associated with autosomal dominant erythrocytosis and pulmonary hypertension.