Muscular dystrophies: diagnostic approaches in Hungary

Muscular dystrophies are a genetically heterogeneous group of degenerative muscle disorders. This article focuses on two severe forms of muscular dystrophies and provides genetic data for a large cohort of Hungarian patients diagnosed within the last few years by the authors. The Duchenne/Becker muscular dystrophy (DMD/BMD) is caused by mutations in the dystrophin gene, which is located on chromosome Xp21. The genetic analysis of dystrophin is usually performed by multiplex polymerase chain reaction (PCR), which detects approximately 95% of all deletions but does not distinguish between one and two copies of the exons investigated. The present work, therefore, concentrates on the improvement of the diagnostic panel for the analysis of DMD/BMD in Hungary. Radioactively labelled cDNA probes, encompassing the whole dystrophin gene detect all the deletions and the analysis is quantitative. In addition, the new multiple ligation-dependent probe amplification (MLPA) technique was recently introduced that enabled more reliable and faster quantitative detection of the entire dystrophin gene. The genomic basis of facioscapulohumeral muscular dystrophy (FSHD) is associated with contraction of the D4Z4 repeat region in the subtelomere of chromosome 4q. In case of FSHD, molecular genetic criteria still have to be improved because of the complexity of the disorder.

Rare case of exomphalos complicated with umbilical cord teratoma in a fetus with trisomy 13

An exomphalos containing unusual solid and cystic mass was diagnosed during a routine ultrasound examination in the 17th week of gestation. Further investigations were planned but the pregnancy was terminated. The fetopathological examination revealed an umbilical cord teratoma. Although this entity is very rare it should be emphasized as a possible differential diagnosis when cystic lesion of the cord is detected. Large teratomas associated with abdominal wall defect may have poor fetal outcome and can be associated with structural and chromosomal abnormalities. In our case trisomy 13 was diagnosed.

[First attempts in preimplantation genetic diagnosis: genetic analysis]

Preimplantation genetic diagnosis is a new approach for the prevention of genetic disorders, which provides a healthy pregnancy avoiding the need for its possible termination. The combination of in vitro fertilization techniques and single cell molecular genetic diagnosis allows only unaffected embryos to be selected for transfer to the uterus. It is an acceptable alternative of prenatal diagnosis for certain couples. Here we report our first attempts in the application of fluorescent PCR for sex determination and the detection of the delta-F508 mutation in human blastomeres. We modelled clinical PGD situations as we performed sex determination on 23 preembryos. Sex determination was successful is 20 preembryos (83%). We performed the detection of the delta-F508 mutation on 23 preembryos, which was successful in 20 preembryos (87%). Our experience suggests, that the established fluorescent PCR analysis is a reliable method for PGD, which enables us to apply it for clinical preimplantation genetic diagnosis.

[First attempts in preimplantation genetic diagnosis: blastomere biopsy]

There is an increasing expectation from couples that serious inherited diseases should be recognized at the earliest stages of embryonic development. A valuable tool for early prenatal diagnosis, preimplantation genetic diagnosis (PGD), involves the removal of 1 or 2 blastomeres from an in vitro fertilized embryo with micromanipulator (blastomere biopsy) without affecting the viability of the embryo. Genetic analysis of the removed blastomeres is performed to determine whether the embryo carries the genes responsible for the examined disease. Based on the results of the genetic analysis it is possible to transfer only unaffected embryos to the uterus. In this study, the authors performed blastomere biopsy on 35 embryos at the 6-10 cells stage. A total of 104 blastomeres were analyzed. On follow-up, 64% of biopsied embryos were cleaved and 43% developed to the morula or blastocyst stage. The introduction of this new procedure into the field of assisted reproduction can provide an alternative for couples who do not want to give birth to children affected by a genetic disease but would reject induced abortion after a positive prenatal diagnosis.

[Confirmation of a prenatal diagnosis of trisomy 13 with comparative genomic hybridization (CGH)]

Trisomy 13 was diagnosed with genetic amniocentesis in a fetus of a 50 years old patient. Fetopathologic examination has shown cyclopy, proboscis and semilobar holoprosencephaly of the fetus, which is consistent with Patau syndrome. DNA was extracted from frozen liver tissue. Result of comparative genomic hybridization (CGH) was consistent with trisomy 13. They processed the DNA according Kallioniemi's method with modifications. CGH was developed for cancer genetics in mid 90s and now it is widely used in prenatal diagnosis too. CGH allows global analysis to detect unbalanced chromosome gains and losses in the whole genome in a single experiment without the need for cell culture. Significant results can be expected in those cases where conventional cytogenetics is not able to provide an answer either because postmortem tissue is not appropriate for cytogenetics or because the chromosomal change is sub-microscopical. CGH is a fluorescent in situ hybridization on a healthy target metaphase, with equal amount of competitive hybridization of green labelled digested test DNA and red labelled digested control DNA. Red to green ratio is assessed with the help of an image analyser. Green dominance represents chromosome gain, while red shift chromosome loss. In the paper they present the fetopathologic report of a trisomy 13 fetus and illustrate the method being the first Hungarian obstetric case diagnosed by CGH.

[Pre- and perinatal aspects of hemophilia A and B]

Authors investigate in a retrospective study obstetrical and genetical data in 20 years period of 149 pregnancies of patients turning to genetical counselling because of haemophilia A and B. In case of heterozygote mother there have been fetal determination of sex, and in case of male fetus, there have been DNA examination in 23 of the 35 cases. In case of sick male fetus the couple made a decision on keeping the pregnancy or not, knowing well the genetical risk. Haemophilia A occurred in case of 135 pregnancies (98 pregnancies of 55 heterozygote mothers, and 37 pregnancies from 20 sick fathers). Haemophilia B occurred in case of 14 pregnancies (9 pregnancies of 3 heterozygote mothers, and 5 pregnancies from 4 sick fathers). In case of haemophilia A heterozygote pregnant women there were 32 proven male fetuses, and in 22 cases there have been DNA examinations. In 16 cases there have been artificial abortions (in 10 cases proven disease by DNA examination), and 4 sick male newborns were born from the 16 deliveries (the disease was proven during pregnancy by DNA examination). One male newborn (healthy) was born from the 3 proven male fetuses of haemophilia B heterozygote pregnant women, in 2 cases there have been artificial abortions (in one case on the basis of DNA diagnostics). In cases of heterozygote mothers (haemophilia A and B altogether) the ration of the spontaneous abortions was 13.1%. The rations of the premature deliveries (8.2%) and the Caesarean sections (8.2%) were not higher than the national average. The ration of the bleeding complications during pregnancy was 18.7%, in 2.7% of the cases transfusion was necessary. In case of sickness of the father (in heterozygote female fetuses the haemostasis may change from the fetal side) the ration of the bleeding complications during pregnancy was 18.2%. In connection with delivery, obstetrical bleeding complications occurred in 12.2%, atonia in 2%, abrasion after delivery in 4.1, transfusion in 10.2% in cases both of haemophilia A and B heterozygote mothers. From the neonatological complications in one case there was cerebral haemorrhage, and in one case bleeding from the umbilical stump. (Both newborns were male with haemophilia.) In connection with delivery there was no haematoma developing on the skull of the newborns, there was no need of giving transfusion. In case of sickness of the fathers the ration of the instrumental uterine examination was 6.7%, there were no neonatological and other obstetrical complications.

Apolipoprotein E allele distribution in trisomy 13, 18, and 21 conceptuses in a Hungarian population

Reports documented a higher frequency of apolipoprotein E (apoE) allele epsilon 4 among mothers of children diagnosed with Down syndrome. We studied the prevalence of apoE alleles among 56 conceptuses with trisomy 13, trisomy 18, or trisomy 21. The presence of the 3 most common apoE alleles (epsilon 2, epsilon 3, epsilon 4) was determined by polymerase chain reaction-restriction fragment length polymorphism, and trisomy status was detected by fluorescent polymerase chain reaction followed by DNA fragment analysis and by conventional cytologic methods. We found no significant difference in the distribution of apoE alleles in the group of trisomy 21 fetuses compared with samples from healthy blood donors. The odds of having trisomy 18 for the apoE epsilon 4 group was 3-fold as high as for apoE epsilon 3 allele compared with the healthy control group. Furthermore, a statistically significant association was found for those with trisomy 18 and apoE epsilon 4, while for those with trisomy 13 and apoE epsilon 4, the test showed no significant association. The observed apoE allele epsilon 3 frequencies among patients with Down syndrome and healthy control subjects may help explain and support previous work that did not find high rates of atherosclerosis among these persons. The role of apoE alleles in the development of trisomies needs further study.