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Educational Use Only - Embryology is an educational resource for learning concepts in embryological development, no clinical information is provided and content should not be used for any other purpose.


Monosomy refers to the presence of only one chromosome from the normal pair in the embryo. A partial monosomy is when there is only one copy of a segment of a chromosome present.

A complete monosomy syndrome in female humans is seen in Turner syndrome (Monosomy X) associated with either a missing or altered second X chromosome.

A partial monosomy syndrome in humans is seen in Cri du Chat (cat's cry) syndrome associated with a piece of chromosome 5 is missing.

Other described autosomal monosomies include chromosomes: 3, 7, 11 Jacobsen Syndrome, 18 Monosomy 18p Syndrome and 21.

Genetic Links: genetic abnormalities | maternal age | Trisomy 21 | Trisomy 18 | Trisomy 13 | Trisomy X | Monosomy | Fragile X | Williams | Alagille | Philadelphia chromosome | mitochondria | hydatidiform mole | epigenetics | Prenatal Diagnosis | Neonatal Diagnosis | meiosis | mitosis | International Classification of Diseases | genetics

Genital System - Abnormalities

Some Recent Findings

  • Turner syndrome-issues to consider for transition to adulthood[1] "Turner syndrome (TS) is associated with a spectrum of health problems across the age span, which requires particular attention during the transition period in these adolescents. The majority of girls with TS require oestrogen replacement from puberty onwards, which is important for adequate feminization, uterine development and maintenance of bone health. There is a lifetime increased risk from autoimmune conditions like hypothyroidism, coeliac disease, hearing loss and aortic dilatation with the potential to lead to aortic dissection. A systematic and holistic approach to provision of health care in TS is needed."
More recent papers  
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Search term: Monosomy

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International Classification of Diseases


Chromosomal abnormalities, not elsewhere classified (Q90-Q99)

Q93 Monosomies and deletions from the autosomes, not elsewhere classified

Q96 Turner's syndrome Excl.: Noonan's syndrome (Q87.1)

Links: International Classification of Diseases

Prenatal Diagnosis

The most common prenatal diagnosis is by either amniocentesis or chorionic villi sampling.

Amniocentesis.jpg Cvs.jpg

Links:Amniocentesis | Chorionic villus sampling


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Monosomy X

Turner's syndrome karyotype

Monosomy XO or Turner's syndrome results in 99% non-viable embryos, viable development fail to sexually mature at puberty.

Named after Henry Turner (1938), an American clinician who first described the condition.

Turner Syndrome X Chromosome Variations.jpg Figure shows Turner syndrome variations of the second X chromosome.
  • Completely absent (45,X)
  • Partially absent
  • Forms an isochromosome (isoXq), possessing a long arm duplication (q) and being devoid of a short arm (p)
  • In a ring formation (rX)
  • Is devoid of the homeobox gene, SHOX (short stature homeobox), the deletion being prior to the junction between Xp22.2 and Xp22.3

ICD-11 Descriptions

Karyotype 45, X

  • Karyotype missing one X chromosome (45, X0 or 45,XO/46,XX mosaicism) ; gonads: ovaries (streak); phenotype female with short stature, amenorrhea (hypergonadotrophic hypogonadism), absence of sexual development, webbed neck, low set ears, posterior hairline, widely-spaced nipples, short fourth metacarpals, and increased carrying angle at the elbow (cubitus valgus). Often associated with renal, cardiac and ocular abnormalities.

Karyotype 46, X iso Xq

  • A disease affecting females, caused by one of the two X chromosomes consisting of two q arms, which are structurally identical and contain the same genes. This disease may present with short stature, extra folds of skin on the neck, a low hairline at the back of the neck, puffiness or swelling of the hands and feet, skeletal abnormalities, ovarian hypofunction or premature ovarian failure, kidney problems, or heart defects. This disease may be differentiated from classical Turner Syndrome by a near complete lack of gonadal development, resulting in a lack of menstruation or breast development. Confirmation is through observation of an iso Xq chromosome by karyotyping.

Mosaicism, 45, X, 46, XX or XY

  • A disease caused by embryonic fusion, or by the loss of one of the sex chromosomes from a cell early in embryonic development; Gonadal status: normal or variable abnormalities of sexual anatomy, maturation or function. Phenotype: normal, or abnormal sexual development.

Monosomy 18p Syndrome

Monosomy 18p syndrome facial features.jpg

Monosomy 18p syndrome facial features[2]

A flat midface, mild ptosis, large ears with detached pinnae and short protruding upper lip.

Jacobsen Syndrome

Jacobsen syndrome (JS) is a rare partial deletion of the long arm of chromosome 11.[3]

Cri du Chat Syndrome

Chromosome 5P deletions
Chromosome 5P deletions[4]

Chromosome 5P Deletion Syndrome or "Cri du Chat" (cat's cry) is a partial monosomy syndrome occurring in humans (1:15,000 to 1:50,000 live-born infants) associated with a piece of chromosome 5 is missing, see reviews.[4][5]

Cri du Chat - audio recording

Clinical Features Malformations (infrequently associated)
  • high-pitched monochromatic cry
  • severe psychomotor retardation.
  • severe mental retardation.
  • microcephaly
  • broad nasal bridge
  • epicanthal folds
  • micrognathia
  • abnormal dermatoglyphics
  • cardiac
  • other neurological
  • renal abnormalities
  • preauricular tags
  • syndactyly
  • hypospadias
  • cryptorchidism
Links: OMIM123450 | Cri du Chat - audio recording


  1. Lucaccioni L, Wong SC, Smyth A, Lyall H, Dominiczak A, Ahmed SF & Mason A. (2015). Turner syndrome--issues to consider for transition to adulthood. Br. Med. Bull. , 113, 45-58. PMID: 25533182 DOI.
  2. Turleau C. (2008). Monosomy 18p. Orphanet J Rare Dis , 3, 4. PMID: 18284672 DOI.
  3. Mattina T, Perrotta CS & Grossfeld P. (2009). Jacobsen syndrome. Orphanet J Rare Dis , 4, 9. PMID: 19267933 DOI.
  4. 4.0 4.1 Cerruti Mainardi P. (2006). Cri du Chat syndrome. Orphanet J Rare Dis , 1, 33. PMID: 16953888 DOI.
  5. Rodríguez-Caballero A, Torres-Lagares D, Rodríguez-Pérez A, Serrera-Figallo MA, Hernández-Guisado JM & Machuca-Portillo G. (2010). Cri du chat syndrome: a critical review. Med Oral Patol Oral Cir Bucal , 15, e473-8. PMID: 20038906


Agarwal P, Philip R, Gutch M & Gupta KK. (2013). The other side of Turner's: Noonan's syndrome. Indian J Endocrinol Metab , 17, 794-8. PMID: 24083159 DOI.

Hong D, Scaletta Kent J & Kesler S. (2009). Cognitive profile of Turner syndrome. Dev Disabil Res Rev , 15, 270-8. PMID: 20014362 DOI.

Turleau C. (2008). Monosomy 18p. Orphanet J Rare Dis , 3, 4. PMID: 18284672 DOI.

Cerruti Mainardi P. (2006). Cri du Chat syndrome. Orphanet J Rare Dis , 1, 33. PMID: 16953888 DOI.

Ross J, Zinn A & McCauley E. (2000). Neurodevelopmental and psychosocial aspects of Turner syndrome. Ment Retard Dev Disabil Res Rev , 6, 135-41. PMID: 10899807 <135::AID-MRDD8>3.0.CO;2-K DOI.


Ross JL, Roeltgen D, Kushner H, Wei F & Zinn AR. (2000). The Turner syndrome-associated neurocognitive phenotype maps to distal Xp. Am. J. Hum. Genet. , 67, 672-81. PMID: 10931762 DOI.

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Cite this page: Hill, M.A. (2019, February 18) Embryology Monosomy. Retrieved from

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