Monosomy disorders occur during fetus development and are characterized by a partial or full missing pair of a chromosome. While these disorders are relatively rare, the most common are Turner syndrome and Cri du chat syndrome. Other disorders, such as 1p36 deletion syndrome and Alfie's syndrome, are extremely rare. Turner syndrome is the only full monosomy that is compatible with life; every other type is fatal either in the womb or directly after birth. Those living with a monosomy disorder other than Turner syndrome have a partial monosomy, meaning that only one piece of one side of a chromosome is missing.
Turner syndrome affects approximately one in 2,500 women. The chromosome pair that determines the female sex, known as XX, is missing one of the Xs in Turner syndrome. Without treatment, women with this monosomy disorder will only grow to under 5 feet (1.5 meters) and will not go through puberty. With the use of growth hormones and estrogen replacement early on, these issues can be avoided, although patients will always be infertile.
Turner syndrome can also cause some learning delays, especially in math, and can cause some physical abnormalities such as a webbed neck, droopy eyelids, and excessive moles. With early treatment and therapy, those with Turner syndrome can typically attend class with their atypical peers and go on to live independently. In some cases, an egg donor coupled with IVF treatment can help them to carry and birth a child naturally.
Cri du chat syndrome, meaning “cry of the cat” in French, is a monosomy disorder related to a missing part of chromosome 5. Along with several learning and physical disabilities, this disorder causes the larynx to develop abnormally, resulting in a distinctive cry under the age of 2. Physically, those with Cri du chat often have a smaller than usual head, round face, and very wide set eyes. They also often have heart defects, poor muscle tone, and difficulty functioning in social settings, and often display very aggressive or unpredictable behavior. While no medical treatment is available for this disorder, therapy treatments can often help patients with intellectual disabilities and socialization.
1p36 deletion syndrome, i.e., a missing part of chromosome 1, can cause several physical and mental disabilities, including facial deformities and severe learning delays. This monosomy disorder is much more rare than Turner or Cri du chat syndrome; therapy for learning delays and social interaction are the only treatments available. Alfie's syndrome, a missing part of chromosome 9, has less than 100 reported cases in the world, making it the rarest monosomy disorder.
The health issues as well as the facial and mental abnormalities present with Alfie's syndrome are severe, although some cases have been found where the intellectual disability of the patient drastically improved following therapy. In one case, a child went from profoundly intellectually disabled, an IQ score of under 20, to below average on the IQ scale, meaning above 70 points. With the absence of severe health issues such as heart defects, those with these disorders typically have a long lifespan, usually 50 and 70 years. Due to the fact that many different parts of a chromosome can be missing, the severity of these disorders varies greatly by patient.