With respect to pure developmental dyscalculia, domain-general causes are unlikely as they should not impair ones ability in the numerical domain without also affecting other domains such as reading.Two competing domain-specific hypotheses about the causes of developmental dyscalculia have been proposed – the magnitude representation (or number module deficit hypothesis) and the access deficit hypothesis. Magnitude representation deficit
Dehaenes "number sense" theory suggests that approximate numerosities are automatically ordered in an ascending manner on a mental number line. The mechanism to represent and process non-symbolic magnitude (e.g., number of dots) is often known as the "approximate number system" (ANS), and a core deficit in the precision of the ANS, known as the "magnitude representation hypothesis" or "number module deficit hypothesis", has been proposed as an underlying cause of developmental dyscalculia.In particular, the structural features of the ANS is theoretically supported by a phenomenon called the "numerical distance effect", which has been robustly observed in numerical comparison tasks. Typically developing individuals are less accurate and slower in comparing pairs of numbers closer together (e.g., 7 and 8) than further apart (e.g., 2 and 9). A related "numerical ratio effect" (in which the ratio between two numbers varies but the distance is kept constant, e.g., 2 vs. 5 and 4 vs. 7) based on the Webers law has also been used to further support the structure of the ANS.
Chronic mountain sickness (CMS) is a disease in which the proportion of blood volume that is occupied by red blood cells increases (polycythaemia) and there is an abnormally low level of oxygen in the blood (hypoxemia). CMS typically develops after extended time living at high altitude (over 2,500 metres (8,200 ft)). It is most common amongst native populations of high altitude nations. The most frequent symptoms of CMS are headache, dizziness, tinnitus, breathlessness, palpitations, sleep disturbance, fatigue, loss of appetite, confusion, cyanosis, and dilation of veins.CMS was first described in 1925 by Carlos Monge Medrano, a Peruvian doctor who specialised in diseases of high altitude. While acute mountain sickness is experienced shortly after ascent to high altitude, chronic mountain sickness may develop only after many years of living at high altitude. In medicine, high altitude is defined as over 2,500 metres (8,200 ft), but most cases of CMS occur at over 3,000 metres (9,800 ft). It has recently been correlated with increased expression of the genes ANP32D and SENP1. Diagnosis
CMS is characterised by polycythaemia (with subsequent increased haematocrit) and hypoxaemia; raised blood pressure in the lungs (pulmonary hypertension) can develop over time and in some cases progress to heart failure (cor pulmonale). CMS is believed to arise because of an excessive production of red blood cells (erythrocytes) due to the low oxygen levels at altitude, which increases the oxygen carrying capacity of the blood[1]. The increased levels of erythrocytes causes increased blood viscosity and uneven blood flow through the lungs (V/Q mismatch).