Prader-Willi syndrome - type 1 deletion, a consequence of an unbalanced translocation of chromosomes 13 and 15, easily to be mixed up with a Robertsonian translocation

Frenny Sheth,Jayesh Sheth,Thomas Liehr,Krati Shah

doi:10.1186/s13039-015-0163-2

Frenny Sheth, Jayesh Sheth + Show 2 more

Open Access

https://doi.org/10.1186/s13039-015-0163-2

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Abstract

BackgroundPrader-Willi syndrome, due to microdeletion of proximal 15q, is a well-known cause of syndromic obesity.Case characteristicsA couple with history of repeated first trimester abortions had a son with balanced Robertsonian translocation of chromosomes 13 and 15 according to cytogenetic banding technique.ResultsChromosomal analysis for the couple was performed. A balanced translocation involving BP1-BP3 region of proximal 15q was observed in the father.DiscussionInvestigations of the parents is mandatory when a structural rearrangement is detected in a dysmorphic child.

Highlights

Prader-Willi syndrome, due to microdeletion of proximal 15q, is a well-known cause of syndromic obesity
Prader-Willi syndrome (PWS) can be due to distinct genetic mechanisms: deletion of paternally expressed functional genes, maternal uniparental disomy and imprinting defects of genes in proximal 15q
We present a rare case of PWS arisingas a consequence of paternally inherited unbalanced translocation involving chromosome 13 and 15 resulting in loss of proximal 15q, which can be misinterpreted as Robertsonian translocation

Summary

Background

Prader-Willi syndrome (PWS) is a neurobehavioral genetic disorder (OMIM #176270) characterized by hypotonia, poor feeding in infancy, hyperphagia with evolving obesity in later live, hypogonadism, decreased adult height as well as cognitive and behavioural disabilities [1]. We present a rare case of PWS arisingas a consequence of paternally inherited unbalanced translocation involving chromosome 13 and 15 resulting in loss of proximal 15q, which can be misinterpreted as Robertsonian translocation. Further characterization of sSMC was carried out using various probes in 2 to three colour FISH settings probes for the centromeric regions of chromosomes 13/21 (D13/21Z1) and 15 (D15Z4 – both ZytoVision, Bremerhaven, Germany) together with a homemade probe for all acrocentric short arms (midi54 = acro-p-arm) and BAC probes RP11-446P9 (in 15p12) together with RP11-408 F10 in 15 q13.1 This substantiated that the sSMC was a “by-product” of a balanced paternal translocation involving one chromosome 13 and 15 and mimicking a Robertsonian translocation.Breakpoints were located in 13p11.2 and 15q13.2 region and the karyotype was redefined as 46,XY,t(13;15)(p11.2;q13.2) (Fig. 1a). The proband had an unbalanced karyotype 45,XY,der(13)t(13;15)(p11.2; q13.2),-der(15)t(13;15)(p11.2;q13.2)

Discussion

Conclusion