No increase in the CTG repeat size during transmission from parent with expanded allele: false suspicion of contraction phenomenon

Nuria Goñi Ros; Paula Sienes Bailo; Ricardo González Tarancón; Loreto Martorell Sampol; Silvia Izquierdo Álvarez

doi:10.1515/almed-2022-0079

No increase in the CTG repeat size during transmission from parent with expanded allele: false suspicion of contraction phenomenon

Adv Lab Med. 2023 Mar 6;4(2):185-194. doi: 10.1515/almed-2022-0079. eCollection 2023 Jun.

[Article in English, Spanish]

Authors

Nuria Goñi Ros¹, Paula Sienes Bailo¹, Ricardo González Tarancón¹, Loreto Martorell Sampol², Silvia Izquierdo Álvarez¹

Affiliations

¹ Servicio de Genética y Bioquímica Clinica, Hospital Universitario Miguel Servet, Zaragoza, Spain.
² Servicio de Medicina Genética y Molecular, Hospital Sant Joan de Déu, Barcelona, Spain.

Abstract

Objectives: Myotonic dystrophy type 1 (DM1), also known as Steinert's disease, is a chronic, progressive and disabling multisystemic disorder with a broad spectrum of severity that arises from an autosomal-dominant expansion of the Cytosine-Thymine-Guanine (CTG) triplet repeat in the 3' untranslated region of the DMPK gene (19q13.3).

Case presentation: In this study, we report the case of a family with several intergenerational expansions of the CTG repeat, with an additional case of a false suspicion of contraction phenomenon due to TP-PCR limitations.

Conclusions: The meiotic instability of the (CTG)_n repeats leads to genetic anticipation where increased size of DM1 mutation and a more severe phenotype have been reported in affected individuals across generations. Even if extremely rare, a decrease in the CTG repeat size during transmission from parents to child can also occur, most frequently during paternal transmissions.

Keywords: DMPK; TP-PCR limitations; myotonic dystrophy type 1; trinucleotide repeats.

Publication types

Case Reports