Conditions That Can Cause Hypotonia (Low Muscle Tone)

Noonan Syndrome

Noonan syndrome in an individual can cause them to be born with hypotonia. Noonan syndrome describes a group of symptoms including short stature, bleeding problems, unusual facial features, heart defects, and skeletal malformations caused by certain genetic mutations. The genes typically affected in Noonan syndrome include PTPN11, SOS1, and less commonly, RAF1 and RIT1. A small number of cases of this condition have an unknown cause. These mutations cause a process that leads to a disturbance in the normal regulation of cell division and cell growth. These disturbances cause growth restriction and skeletal system malformations that result in facial abnormalities, delay in puberty, and short stature. Hypotonia in Noonan syndrome patients is most likely attributed to their poor growth. Infants born with this disorder are usually an average length but do not grow taller at the same rate as healthy children. While the bones do not grow properly, the muscles often do grow at a normal rate. Hypotonia is the result because the larger muscles are unable to provide adequate tension or resistance to the movement because the bones are disproportionally too short.

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