XYYYY syndrome

XYYYY syndrome, also known as 49,XYYYY, is an exceptionally rare chromosomal disorder in which a male has three additional copies of the Y chromosome. Only seven non-mosaic cases of the disorder have ever been recorded in the medical literature, as well as five mosaic cases, of which two had more 48,XYYY than 49,XYYYY cells.[1] Due to the extreme rarity of the disorder, little is understood about it,[2] and the phenotype appears to be variable.[3]

Phenotype

XYYYY syndrome is associated with developmental and skeletal anomalies that are also observed in other sex chromosome aneuploidies. Findings associated with the karyotype include hypertelorism (wide-spaced eyes), low-set ears, radioulnar synostosis (fusion of the long bones in the forearm), and clinodactyly (incurved pinky fingers).[2] Intellectual disability has been observed in all cases old enough to test[3] and is in the mild to moderate range.[1][note 1] Though other Y-chromosome polysomy disorders are associated with tall stature,[5] this does not appear to be true in XYYYY syndrome, with recorded heights ranging from the 10th to 97th percentile.[3] Autism and attention-deficit hyperactivity disorder are both thought to be associated with the syndrome.[1] External genitalia are normal, but testicular insufficiency appears to develop during childhood and lead to adult azoospermia.[2]

History

Non-mosaic XYYYY syndrome was first recorded in 1981 in a 14-month-old boy, though a mosaic case with mixed 49,XYYYY and 45,X0 cells had been recorded in 1968.[6] This case was followed up at the age of seven, providing the only known long-term follow-up of the disorder.[3] Only two adults with XYYYY syndrome have been described.[1]

Prevalence

The disorder's prevalence is estimated to be below 1 in 1,000,000.[4]

See also

Notes
  1. While some writers suggest intellectual disability is moderate to severe,[4] this has not been recorded in any descriptions of the disorder.[1]

References
  1. Demily C, Poisson A, Peyroux E, Gatellier V, Nicolas A, Rigard C, Schluth-Bolard C, Sanlaville D, Rossi M (2017). "Autism spectrum disorder associated with 49,XYYYY: case report and review of the literature". BMC Medical Genetics. 18 (9): 9. doi:10.1186/s12881-017-0371-1. PMC 5282903. PMID 28137251.
  2. Linden MG, Bender BG, Robinson A (October 1995). "Sex chromosome tetrasomy and pentasomy". Pediatrics. 96 (4): 672–682. doi:10.1542/peds.96.4.672. PMID 7567329.
  3. Frey-Mahn G, Behrendt G, Geiger K, Sohn C, Schäfer D, Miny P (12 December 2002). "Y chromosomal polysomy: A unique case of 49,XYYYY in amniotic fluid cells". American Journal of Medical Genetics. 118A (2): 184–186. doi:10.1002/ajmg.a.10051. PMID 12655500. S2CID 37103837.
  4. "49,XYYYY syndrome". Orphanet. Retrieved 3 May 2021.
  5. Bartholdi D, Schinzel A (2009). "Y Polysomies, in Males". In Lang F (ed.). Encyclopedia of Molecular Mechanisms of Disease. Berlin: Springer-Verlag. pp. 2265–2266. doi:10.1007/978-3-540-29676-8_1908. ISBN 978-3-540-67136-7.
  6. Sirota L, Zlotogota Y, Shabtai F, Halbrecht I, Elian E (1981). "49, XYYYY. A case report". Clinical Genetics. 19 (2): 87–93. doi:10.1111/j.1399-0004.1981.tb00676.x. PMID 7471512. S2CID 36727592.
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