3-M syndrome

3-M syndrome is a disorder that causes skeletal abnormalities including short stature (dwarfism) and unusual facial features. The name of this condition comes from the initials of three researchers who first identified it: Miller, McKusick, and Malvaux.

Individuals with 3-M syndrome grow extremely slowly before birth, and this slow growth continues throughout childhood and adolescence. They have low birth weight and length and remain much smaller than others in their family, growing to an adult height of approximately 4 feet to 4 feet 6 inches (120 centimeters to 130 centimeters). In some affected individuals, the head is normal-sized but looks disproportionately large in comparison with the body. In other people with this disorder, the head has an unusually long and narrow shape (dolichocephaly). Intelligence is unaffected by 3-M syndrome, and life expectancy is generally normal.

In addition to short stature, people with 3-M syndrome have a triangle-shaped face with a broad, prominent forehead (frontal bossing) and a pointed chin; the middle of the face is less prominent (hypoplastic midface). Other common features include large ears, full eyebrows, an upturned nose with a fleshy tip, a long area between the nose and mouth (philtrum), a prominent mouth, and full lips.

Other skeletal abnormalities that often occur in this disorder include a short, broad neck and chest; prominent shoulder blades; and shoulders that slope less than usual (square shoulders). Affected individuals may have abnormal spinal curvature such as a rounded upper back that also curves to the side (kyphoscoliosis) or exaggerated curvature of the lower back (hyperlordosis). People with 3-M syndrome can also have unusual curving of the fingers (clinodactyly), short fifth (pinky) fingers, prominent heels, and loose joints. Additional skeletal abnormalities, such as unusually slender long bones in the arms and legs; tall, narrow spinal bones (vertebrae); or slightly delayed bone age may be apparent in x-ray images.

A variant of 3-M syndrome called Yakut short stature syndrome has been identified in the isolated Yakut population in the Russian province of Siberia. In addition to having most of the physical features characteristic of 3-M syndrome, people with this form of the disorder are often born with breathing problems that can be life-threatening in infancy.