Marshall-Smith syndrome causes faster physical growth and bone development, which causes a failure to thrive. People with Marshall-Smith syndrome are usually underweight, and experience muscle weakness and mental retardation. Respiratory issues, excessive hair growth, and abnormal facial structures such as long head, prominent eyes and forehead, and upturned nose, are other symptoms of Marshall-Smith syndrome. The cause of this condition is still unknown, but it is not thought to be genetic. Marshall-Smith syndrome is a rare condition that occurs in both females and males, and more research is necessary to determine the cause of this syndrome. Currently, the best hypothesis for the cause of Marshall-Smith syndrome is de novo mutation, which means a mutation in either the egg or sperm cell or in the fertilized cell.
Marshall-Smith syndrome is a condition that occurs from birth and is determined by certain facial characteristics, such as a wide and prominent forehead, eyes that are wide and protrude, small chin and small, upturned nose, as well as advanced bone maturation for the age they are at, difficulty or failure to grow, severe respiratory problems, and difficulty to gain enough weight to be deemed "appropriate for an individual's age." It is expected that those with MSS (Marshall-Smith syndrome) will have mental and physical delays and are more prone to getting pneumonia due to problems with the structure of the larynx and trachea in many cases. This is due to the fact that the larynx and trachea tend to be soft and less muscular and cannot function properly. This can lead to the airways becoming blocked and mucus can build up causing too much bacteria which can lead to pneumonia. Ear infections are also typical for those with MSS. It can also be difficult for children to eat due to muscles not being very strong in the throat.
Advanced bone age is shown in anyone with MSS. Advanced bone age means that the bones of the individual appear to be more dense on X-rays than they should be for their age.
Other less common symptoms may include a," blue-tinged sclerae (the white sections of the eyes), a large head circumference, and a small, triangle-shaped face.)." Creases in the hands tend to be deeper than usual. The big toe may appear to be bigger and longer than usual as well. "Additional features include hirsuitism and umbilical hernia. Hearing loss can sometimes occur. Ears may be larger, have a "crumpled" appearance, or be lower on the head than usual." Brain abnormalities are also common for those with MSS.
There has only been one case to show that MSS may stem from a genetic abnormality, but almost every other has shown no genetic relation to MSS. So far it is know to mainly be a random syndrome that is very rare.