Both domain-general and domain-specific causes have been put forth. With respect to pure developmental<unk> , domain-general causes are unlikely as they should not impair one's ability in the numerical domain without also affecting other domains such as reading. Two competing domain-specific hypotheses about the causes of developmental<unk>  have been proposed – the magnitude representation (or number module deficit hypothesis) and the access deficit hypothesis. Magnitude representation deficit Dehaene's "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<unk> . 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 Weber's law has also been used to further support the structure of the ANS. The numerical ratio effect is observed when individuals are less accurate and slower in comparing pairs of numbers that have a larger ratio (e.g., 8 and 9, ratio = 8/9) than a smaller ratio (2 and 3; ratio = 2/3). A larger numerical distance or ratio effect with comparison of sets of objects (i.e., non-symbolic) is thought to reflect a less precise ANS, and the ANS acuity has been found to correlate with math achievement in typically developing children and also in adults. More importantly, several behavioral studies have found that children with developmental<unk>  show an attenuated distance/ratio effect than typically developing children. Moreover, neuroimaging studies have also provided additional insights even when behavioral difference in distance/ratio effect might not be clearly evident. For example, Gavin R. Price and colleagues found that children with developmental<unk>  showed no differential distance effect on reaction time relative to typically developing children, but they did show a greater effect of distance on response accuracy. They also found that the right intraparietal sulcus in children with developmental<unk>  was not modulated to the same extent in response to non-symbolic numerical processing as in typically developing children. With the robust implication of the intraparietal sulcus in magnitude representation, it is possible that children with developmental<unk>  have a weak magnitude representation in the parietal region. Yet, it does not rule out an impaired ability to access and manipulate numerical quantities from their symbolic representations (e.g., Arabic digits). This shows the part of the brain where the sulcus is located in the parietal lobe. Moreover, findings from a cross-sectional study suggest that children with developmental<unk>  might have a delayed development in their numerical magnitude representation by as much as five years. However, the lack of longitudinal studies still leaves the question open as to whether the deficient numerical magnitude representation is a delayed development or impairment. Access deficit hypothesis Rousselle & Noël propose that<unk>  is caused by the inability to map preexisting representations of numerical magnitude onto symbolic Arabic digits. Evidence for this hypothesis is based on research studies that have found that individuals with<unk>  are proficient on tasks that measure knowledge of non-symbolic numerical magnitude (i.e., non-symbolic comparison tasks) but show an impaired ability to process symbolic representations of number (i.e., symbolic comparison tasks). Neuroimaging studies also report increased activation in the right intraparietal sulcus during tasks that measure symbolic but not non-symbolic processing of numerical magnitude. However, support for the access deficit hypothesis is not consistent across research studies.
Dyscalculia
Acalculia
Generalized lentiginosis
Penis enlargement
Pattern hair loss
Pearly penile papules
Hyperkatifeia
Hypertrichosis