Monosomy disorders involve missing chromosomes and are rare, with Turner syndrome and Cri du chat syndrome being the most common. Turner syndrome affects one in 2,500 women and can cause growth and puberty issues, learning delays, and physical abnormalities. Cri du chat syndrome causes physical and learning disabilities, as well as a characteristic cry. Other monosomy disorders, such as 1p36 deletion syndrome and Alfie syndrome, are extremely rare and can cause various physical and mental disabilities. Therapy is often the only treatment available, but patients typically have long lifespans.
Monosomy disorders occur during the developing fetus and are characterized by a partial or complete missing pair of a chromosome. Although 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 syndrome, are extremely rare. Turner syndrome is the only complete monosomy compatible with life; every other type is fatal both in utero and soon after birth. Those living with a monosomy disorder other than Turner syndrome have partial monosomy, meaning that only a piece of one side of a chromosome is missing.
Turner syndrome affects about one in 2,500 women. The pair of chromosomes that determine female sex, known as XX, is missing one of the X’s in Turner syndrome. Without treatment, women with this monosomy disorder will only grow under 5 feet (1.5 meters) and will not go through puberty. With early use of growth hormones and estrogen replacement, these problems can be avoided, even though patients will always be infertile.
Turner syndrome can also cause some learning delays, especially in mathematics, and can cause some physical abnormalities such as webbed neck, droopy eyelids, and excessive moles. With early treatment and therapy, those with Turner syndrome can typically attend classes with their atypical peers and continue to live independently. In some cases, an egg donor paired with IVF treatment can help them carry and deliver a baby naturally.
Cri du chat syndrome, which is French for “crying cat”, is a monosomy disorder related to a missing part of chromosome 5. Along with various physical and learning disabilities, this disorder causes the larynx to develop abnormally, with consequent characteristic cry under 2 years of age. Physically, those with Cri du chat often have a smaller-than-usual head, a round face, and very wide eyes. They also often have heart defects, poor muscle tone, and difficulty functioning in social settings, and often display highly aggressive or erratic behavior. While no medical treatment is available for this disorder, therapeutic treatments can often help patients with intellectual disabilities and socialization.
1p36 deletion syndrome, a missing part of chromosome 1, can cause various physical and mental disabilities, including facial deformities and severe learning disabilities. This monosomy disorder is much rarer than Turner syndrome or Cri du chat; therapy for learning disabilities and social interaction are the only treatments available. Alfie syndrome, a missing part of chromosome 9, has fewer than 100 cases reported worldwide, making it the rarest monosomy disease.
The health problems and facial and mental abnormalities present with Alfie syndrome are serious, although there have been some cases where the patient’s intellectual disability improved dramatically after therapy. In one case, a child went from profound intellectual disability, an IQ score of less than 20, to a below-average IQ score of more than 70 points. With the absence of serious health problems such as heart defects, those with these disorders typically have long life spans, usually 50 to 70 years. Due to the fact that many different parts of a chromosome can be missing, the severity of these disorders varies greatly from patient to patient.
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