According to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), learning disorders are among the most frequently diagnosed developmental disorders in childhood. Children experiencing a deficit in one learning domain frequently show deficits in other domains likely due to shared genetic variance.
The definition of a mathematics learning disorder includes well below average mathematical academic performance for age that is not attributable to an intellectual disability (which is defined by IQ below 70) or a predefined discrepancy between IQ and the affected learning domain. 
Neurologic in origin, learning disorders impede a person's ability to store, process, and/or produce information. Learning disorders can affect the ability to read, write, speak, or compute mathematics and can impair socialization skills. The central clinical feature of a learning disorder is the lack of normal developmental skill, either cognitive or linguistic.
Mathematical learning disorder (MD) also known as dyscalculia is a term used for a wide range of disorders caused by abnormalities in one or more of the basic psychological processes involved in understanding or use of math. Several manifestations of the disorder may occur throughout the life of the individual. Mathematical learning disorder does not include children who have learning problems caused primarily by (1) visual, hearing, or motor impairments; (2) mental retardation; (3) emotional disturbance; or (4) environmental, cultural, or economic disadvantages. [2, 3, 4]
US clinicians should become familiar with the federal Individuals with Disabilities Education Act (IDEA), which defines learning disorders as "processing disorders that result in a significant discrepancy between potential and acquisition of various academic or language skills." [5, 6] Although this definition has raised several questions, it remains important in current clinical practice. Mathematical learning disorder is among the disabilities that qualify children for special education programs under IDEA.
Assessing the exact incidence of mathematical learning disorder is difficult due to paucity of studies that focus specifically on basic number and arithmetic skills.
Collectively, learning and language disorders comprise a very common set of problems. An estimated 10–20% of children and adolescents have a language disorder, a learning disorder, or both. Reading disorders (RDs) comprise a large portion of this group. An estimated 3–7% of elementary school children have been identified with mathematical disorder comparable to the percentage with reading and spelling disorder.  However, children often have more than one disorder; 56% of children with a reading disorder also showed poor mathematics achievement, and 43% of children with a mathematical learning disorder showed poor reading skills.
The estimated incidence may not accurately reflect the presence of the disorder. Some children may have narrow deficits in certain aspects of arithmetic (eg, counting) and perform well in all other aspects. However, standardized tests will still record a poor performance.
Mathematical learning disorder incidence among American children is higher than in Japanese, German, or French children. This higher incidence may be linked to the instructional course design.
Although children with developmental dyscalculia perform more poorly during subtraction activities, there appears to be greater activity in multiple intra-parietal sulcus (IPS) and superior parietal lobule subdivisions in the dorsal posterior parietal cortex as well as in the fusiform gyrus in the ventral occipito-temporal cortex. A study of connectivity analyses revealed hyper-connectivity, rather than reduced connectivity, between the IPS and multiple brain systems including the lateral fronto-parietal and default mode networks thus suggesting the possibility that the IPS and its functional circuits are involved with inappropriate task modulation and hyper-connectivity during addition and subtraction tasks as opposed to the theory of under-engagement and under-connectivity. 
Risk factors include very low birth weight due to maternal cigarette (nicotine) smoking, which can contribute to reduced gray matter volume in the intra parietal sulcus. 
Long-term prognosis is guarded as numerical skills have been associated with increased risk for unemployment and stress. The lack of numerical literacy skills can interfere with everyday basic living skills: e.g., not being able to make and keep appointments (due to not being able to judge or tell time), problems with paying bills (which can lead to homelessness), and trouble with the use of social media (passwords) and social interactions (not able to remember phone numbers). 
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