Translocation
The extra chromosome 21 material may also occur due to a Robertsonian translocation in 2–4% of cases. In this situation, the long arm of chromosome 21 is attached to another chromosome, often chromosome 14. In a male affected with Down syndrome, it results in a karyotype of 46XY,t(14q21q). This may be a new mutation or previously present in one of the parents. The parent with such a translocation is usually normal physically and mentally; however, during production of egg or sperm cells, a higher chance of creating reproductive cells with extra chromosome 21 material exists. This results in a 15% chance of having a child with Down syndrome when the mother is affected and a less than 5% probability if the father is affected. The probability of this type of Down syndrome is not related to the mothers age. Some children without Down syndrome may inherit the translocation and have a higher probability of having children of their own with Down syndrome. In this case it is sometimes known as familial Down syndrome. Mechanism
The extra genetic material present in Down syndrome results in overexpression of a portion of the 310 genes located on chromosome 21. This overexpression has been estimated at 50%, due to the third copy of the chromosome present. Some research has suggested the Down syndrome critical region is located at bands 21q22.1–q22.3, with this area including genes for the amyloid precursor protein, superoxide dismutase, and likely the ETS2 proto oncogene. Other research, however, has not confirmed these findings.
Cluttering, a speech and fluency disorder characterized primarily by a rapid rate of speech, which makes speech difficult to understand. Developmental verbal dyspraxia also known as childhood apraxia of speech. Dysarthria is a weakness or paralysis of speech muscles caused by damage to the nerves or brain. Dysarthria is often caused by strokes, Parkinsons disease, ALS, head or neck injuries, surgical accident, or cerebral palsy. Aphasia
Dysprosody is an extremely rare neurological speech disorder. It is characterized by alterations in intensity, in the timing of utterance segments, and in rhythm, cadence, and intonation of words. The changes to the duration, the fundamental frequency, and the intensity of tonic and atonic syllables of the sentences spoken, deprive an individuals particular speech of its characteristics. The cause of dysprosody is usually associated with neurological pathologies such as brain vascular accidents, cranioencephalic traumatisms, and brain tumors. Muteness is the complete inability to speak. Speech sound disorders involve difficulty in producing specific speech sounds (most often certain consonants, such as /s/ or /r/), and are subdivided into articulation disorders (also called phonetic disorders) and phonemic disorders. Articulation disorders are characterized by difficulty learning to produce sounds physically. Phonemic disorders are characterized by difficulty in learning the sound distinctions of a language, so that one sound may be used in place of many. However, it is not uncommon for a single person to have a mixed speech sound disorder with both phonemic and phonetic components. Stuttering (AKA “Dysphemia”)  affects approximately 1% of the adult population.