STAC3 disorder

STAC3 disorder is a genetic condition primarily affecting skeletal muscles, causing weakness and poor muscle tone from birth, and increasing the risk of a severe reaction called malignant hyperthermia.

Overview

STAC3 disorder (formerly known as Native American myopathy) is a condition that primarily affects skeletal muscles, which are muscles that the body uses for movement. People with STAC3 disorder have muscle weakness (myopathy) and poor muscle tone (hypotonia) throughout the body that typically begins at birth.

Muscle weakness underlies many of the characteristic features of STAC3 disorder. Affected individuals may have feeding and swallowing difficulties in infancy. They usually have delayed development of motor skills such as sitting, crawling, standing, and walking. Many have facial features described as "myopathic facies", which include drooping eyelids, sunken cheeks, and a mouth often held in an open position and with the corners turned downward. Other distinctive facial features in people with STAC3 disorder can include a small lower jaw, an opening in the roof of the mouth, low-set ears that slant backward, eye openings that are shorter than average or that point downward (short or downslanting palpebral fissures), or an increased distance between the inner corners of the eyes.

Individuals with STAC3 disorder may also be born with joint deformities that restrict movement (contractures