The importance of direct genetic testing for determining female carriers of the mutation in dystrophinopathies

Abstract

Background/Aim. Duchenne muscular dystrophy (MD) and Becker MD are caused by mutations in the gene for dystrophin (DMD). They are X chromosome-linked reces-sive diseases where males are affected, and females are healthy carriers of the mutation in most cases. It is estimat-ed that 2/3 of mothers of Duchenne MD probands are car-riers, while 1/3 of probands have de novo mutations. The aim of the study was to confirm the carrier status of female members of the families of Duchenne MD/Becker MD probands using direct genetic testing methods. Methods. The study included 38 females from 31 families of Du-chenne MD/Becker MD probands with dele-tion/duplication in the DMD gene. Moreover, 4 cases of prenatal diagnosis of Duchenne MD/Becker MD were in-cluded. The methods of polymerase chain reaction - PCR and the multiplex ligation-dependent probe amplification - MLPA were applied for detecting deletions, i.e., dele-tion/duplication mutations in the DMD gene. Results. In the total of 31 Duchenne MD/Becker MD probands, 87.1% of deletions and 12.9% of duplications of one or more exons in the DMD gene were detected. Of the 29 tested mothers, mutations were found in 17 of them (14 de-letions and 3 duplications). Mutations were detected in 11 (57.9%) out of 19 mothers of probands with the Duchenne MD phenotype and 6 (60%) out of 10 mothers of Becker MD probands. Furthermore, 14 (56%) out of 25 mothers were carriers in probands with deletions, and 3 (75%) out of 4 mothers were carriers in probands with duplications. In the remaining 9 other female relatives of the patients, muta-tions were found in 4. In prenatal diagnosis, we identified a deletion in one male and one female fetus of one single mother who was confirmed as a carrier. Conclusion. The study showed that mothers were carriers in almost 60% of sporadic cases of Duchenne MD/Becker MD with dele-tions and duplications. In addition, the carrier frequency tended to be higher in mothers of the probands with dupli-cations (75%) compared to mothers of probands with dele-tions (56%).

Uvod/Cilj. Dišenova mišićna distrofija (MD) i Bekerova MD su uzrokovane mutacijama u genu za distrofin (DMD). To su recesivne bolesti vezane za X hromozom, od kojih obolevaju muškarci, a žene su uglavnom zdravi nosioci mu-tacije. Procenjeno je da su kod probanada obolelih od Dišenove MD 2/3 majki nosioci mutacije, dok 1/3 pro-banada ima de novo mutaciju. Cilj rada bio je da se potvrdi status nosioca mutacije kod ženskih članova porodica pro-banada obolelih od Dišenove MD/Bekerove MD primenom metoda direktnog genetičkog testiranja. Metode. Studija je obuhvatila ukupno 38 žena iz 31 porodice pro-banada obolelih od Dišenove MD/Bekerove MD sa deleci-jom/duplikacijom u DMD genu. Takođe, u studiju su bila uključena i 4 slučaja Dišenove MD/Bekerove MD otkrivena prenatalnom dijagnostikom. Metoda lančane reakcije poli-meraze (polymerase chain reaction – PCR) i metoda višestrukog umnožavanja vezanih proba (multiplex ligation-dependent probe amplification -MLPA) su korišćene za detekciju delecija, od-nosno delecija/duplikacija mutacija u DMD genu. Rezulta-ti. Kod ukupno 31 probanada obolelih od Dišenove MD/Bekerove MD, utvrđeno je 87,1% mutacija tipa deleci-je i 12,9% mutacija tipa duplikacija jednog ili više egzona u DMD genu. Od 29 testiranih majki probanada, mutacije su nađene kod njih 17 (14 delecija i 3 duplikacije). Mutacije su detektovane kod 11 (57,9%) od 19 majki probanada sa feno-tipom Dišenove MD i kod 6 (60%) od 10 majki probanada obolelih od Bekerove MD. Takođe, kod probanada sa de-lecijom, kod 14 (56%) od 25 majki je potvrđeno da su nosioci mutacije, a kod probanada sa duplikacijom, 3 (75%) od 4 majke su bile nosioci mutacije. Od ostalih 9 ženskih srodnika probanada obolelih od Dišenove MD/Bekerove MD, mutacije su nađene kod nijh 4. Prenatalnom dijagnos tikom utvrđene su delecije kod jednog muškog i jednog ženskog fetusa iste majke koja je bila potvrđena kao nosilac mutacije. Zaključak. Istraživanje je pokazalo da su majke bile nosioci mutacija u skoro 60% izolovanih slučajeva ob-olelih od Dišenove MD/Bekerove MD sa delecijama i duplikacijama. Takođe, učestalost majki nosioca mutacije kod probanada sa duplikaciom (75%) se pokazala višom ne-go kod majki probanada sa delecijom (56%).