Nuclear gene OPA1, encoding a mitochondrial dynamin-related protein, is mutated in dominant optic atrophy.

Optic atrophy type 1 (OPA1, MIM 165500) is a dominantly inherited optic neuropathy occurring in 1 in 50,000 individuals that features progressive loss in visual acuity leading, in many cases, to legal blindness. Phenotypic variations and loss of retinal ganglion cells, as found in Leber hereditary optic neuropathy (LHON), have suggested possible mitochondrial impairment. The OPA1 gene has been localized to 3q28-q29 (refs 13-19). We describe here a nuclear gene, OPA1, that maps within the candidate region and encodes a dynamin-related protein localized to mitochondria. We found four different OPA1 mutations, including frameshift and missense mutations, to segregate with the disease, demonstrating a role for mitochondria in retinal ganglion cell pathophysiology.

Stability of the m.8993T->G mtDNA mutation load during human embryofetal development has implications for the feasibility of prenatal diagnosis in NARP syndrome.

BACKGROUND: Mitochondrial DNA (mtDNA) mutations cause a wide range of serious genetic diseases with maternal inheritance. Because of the high transmission risk and the absence of therapy in these disorders, at-risk couples often ask for prenatal diagnosis (PND). However, because heteroplasmy load (coexistence of mutant and wild-type mtDNA) may vary among tissues and with time, the possibility that a single fetal sample may not reflect the whole neonate impedes prenatal diagnosis of mtDNA diseases. METHODS: We performed 13 prenatal diagnoses for the NARP (neurogenic weakness, ataxia, retinitis pigmentosa) m.8993T-->G mtDNA mutation (p.Leu156Arg) in the ATP synthase subunit 6 gene. Analyses were performed on chorionic villous (CVS) and/or amniocyte samples carried out at various stages of pregnancy, using a method enabling quantification of low DNA amounts. RESULTS: Maternal mutant loads ranged from 0 to 75% in blood and had no predictive value for the fetus status, except for women with no detectable mutant DNA, whose fetuses were consistently mutation-free. In 8/13 PND, mutant load was <30%. These children are healthy at 2-7 years of age. In 5/13 PND, mutant load ranged from 65 to 100%, and parents preferred to terminate the pregnancies (15-22 weeks of gestation). Single-cell analysis of 20 trophoblastic cells and 21 amniocytes isolated from two affected fetuses found an average mutant load close to the overall CVS and amniocyte mutant load, despite striking intercellular variation. The m.8993T-->G mutant loads, assessed in 7, 17, 11, and 5 different tissues from 4 terminations, respectively, were identical in all tissues from a given individual (mean (SD) 78 (1.2)%, 91 (0.7)%, 74 (2)%, and 63 (1.6)% for the 4 fetuses, respectively). CONCLUSIONS: Our results indicate that the placental/amniotic mutant loads do reflect the NARP mutant mtDNA load in the whole fetus, even when the sample amount is small, and suggest that heteroplasmy level remains stable during pregnancy, at least after 10 weeks of gestation. Although these data establish the feasibility of PND for this mutation, assessing more precisely the correlation between mutant load and disease severity should further help in interpreting PND results.

Analysis of mtDNA variant segregation during early human embryonic development: a tool for successful NARP preimplantation diagnosis.

BACKGROUND: Diseases arising from mitochondrial DNA (mtDNA) mutations are usually serious pleiotropic disorders with maternal inheritance. Owing to the high recurrence risk in the progeny of carrier females, "at-risk" couples often ask for prenatal diagnosis. However, reliability of such practices remains under debate. Preimplantation diagnosis (PGD), a theoretical alternative to conventional prenatal diagnosis, requires that the mutant load measured in a single cell from an eight cell embryo accurately reflects the overall heteroplasmy of the whole embryo, but this is not known to be the case. OBJECTIVE: To investigate the segregation of an mtDNA length polymorphism in blastomeres of 15 control embryos from four unrelated couples, the NARP mutation in blastomeres of three embryos from a carrier of this mutation. RESULTS: Variability of the mtDNA polymorphism heteroplasmy among blastomeres from each embryo was limited, ranging from zero to 19%, with a mean of 7%. PGD for the neurogenic ataxia retinitis pigmentosa (NARP) mtDNA mutation (8993T-->G) was therefore carried out in the carrier mother of an affected child. One of three embryos was shown to carry 100% of mutant mtDNA species while the remaining two were mutation-free. These two embryos were transferred, resulting in a singleton pregnancy with delivery of a healthy child. CONCLUSIONS: This PGD, the first reported for a mtDNA mutation, illustrates the skewed meiotic segregation of the NARP mtDNA mutation in early human development. However, discrepancies between the segregation patterns of the NARP mutation and the HV2 polymorphism indicate that a particular mtDNA nucleotide variant might differentially influenced the mtDNA segregation, precluding any assumption on feasibility of PGD for other mtDNA mutations.

Prenatal diagnosis of myopathy, encephalopathy, lactic acidosis, and stroke-like syndrome: contribution to understanding mitochondrial DNA segregation during human embryofetal development.

INTRODUCTION: Myopathy, encephalopathy, lactic acidosis, and stroke-like (MELAS) syndrome, a maternally inherited disorder that is among the most common mitochondrial DNA (mtDNA) diseases, is usually associated with the m.3242A>G mutation of the mitochondrial tRNA(leu) gene. Very few data are available with respect to prenatal diagnosis of this serious disease. The rate of mutant versus wild-type mtDNA (heteroplasmy) in fetal DNA is indeed considered to be a poor indicator of postnatal outcome. MATERIALS AND METHODS: Taking advantage of a novel semi-quantitative polymerase chain reaction test for m.3243A>G mutant load assessment, we carried out nine prenatal diagnoses in five unrelated women, using two different fetal tissues (chorionic villi v amniocytes) sampled at two or three different stages of pregnancy. RESULTS: Two of the five women, although not carrying m.3243A>G in blood or extra-blood tissues, were, however, considered at risk for transmission of the mutation, as they were closely related to MELAS-affected individuals. The absence of 3243A>G in the blood of first degree relatives was associated with no mutated mtDNA in the cardiovascular system (CVS) or amniocytes, and their three children are healthy, with a follow-up of 3 months-3 years. Among the six fetuses from the three carrier women, three were shown to be homoplasmic (0% mutant load), the remaining three being heteroplasmic, with a mutant load ranging from 23% to 63%. The fetal mutant load was fairly stable at two or three different stages of pregnancy in CVS and amniocytes. Although pregnancy was terminated in the case of the fetus with a 63% mutant load, all other children are healthy with a follow-up of 3 months-6 years. CONCLUSION: These data suggest that a prenatal diagnosis for MELAS syndrome might be helpful for at-risk families.

[Preimplantation genetic diagnosis (PGD): results from a Parisian center]. / Indications et résultats du diagnostic pré-implantatoire (DPI).

OBJECTIVE: To report the results of preimplantation genetic diagnosis (PGD) cycles performed in our unit from 2000 to 2004. Materials and methods. One hundred and seventy-one couples were enrolled in the PGD program over this period. The collected oocytes were inseminated by intracytoplasmic sperm injection (ICSI). The resulting embryos were biopsied on the third day of development and the genetic analysis was performed on the same day. Embryo transfers were carried out on the fourth day. RESULTS: The 416 stimulation cycles started yielded 280 oocyte pick-ups, 3506 oocytes retrieved, of which 2966 were suitable for ICSI. Among the 1982 embryos obtained, 1337 embryos were biopsied and genetic diagnosis was performed for 1083 (81%) of them. 381 embryos were transferred during the course of 189 transfer procedures. There were 51 clinical and 46 ongoing (35 single, 11 twin) pregnancies. In addition, 25 frozen embryo replacement cycles were initiated, leading to 6 embryo transfers and 1 ongoing pregnancy. A total of 58 unaffected children were born. CONCLUSION: PGD has gained a place among the choices offered to couples at risk of transmission of a serious and incurable genetic disease. It might be a realistic alternative to prenatal diagnosis for patients carrier of chromosomal rearrangements, single gene defects, X-linked disesases or mitochondrial DNA disorders.

[Extending preimplantation genetic diagnosis to HLA typing: the Paris experience]. / Le diagnostic préimplantatoire couplé au typage HLA: l'expérience parisienne.

Preimplantation genetic diagnosis (PGD) consists in the genetic analysis of one or two cells. These cells (blastomeres) are sampled from embryos, obtained by in vitro fertilization, at the third day of development. Since 1998, the bioethical laws (1994) and their decrees restricted PGD practices in France, strictly to the avoidance of the birth of a child affected with a genetic defect. In parallel, works on blood cord transplantation, taken at the birth of a compatible HLA sibling, showed very encouraging results, particularly for the treatment of Fanconi anemia. In 2001, Verlinsky et al., have reported the first PGD for Fanconi anaemia combined with HLA typing, allowing the birth of a healthy child, HLA-identical with his affected sister. The "designer baby" concept was born. The French law, which allowed PGD under specific conditions, i.e. when the genetic defect has been characterized in one parent at least, recently extended PGD to HLA typing when embryos are at risk of a genetic disorder. Article L.2131-4-1 (August 2004) allows the practice of HLA typing for PGD embryos when an elder sibling is affected with a genetic disorder and need stem cell transplantation. The HLA-matched offspring resulting from PGD can give cord blood at birth to supply the necessary therapy. This double selection give rise to serious ethical problems, but technical difficulties and legal restrictions will probably limit the development of such a procedure.

Prezygotic origin of the isochromosome 12p in Pallister-Killian syndrome.

Pallister-Killian syndrome is a rare disorder comprising multiple congenital anomalies, streaks of hypo(hyper)pigmentation, seizures, profound mental retardation, and the presence of an extra metacentric chromosome i(12)(p10), usually limited to skin fibroblasts. The mechanism and parental origin of the extra chromosome i(12)(p10) are unknown. Here, we present a girl with Pallister-Killian syndrome and the i(12)(p10) in 50% of cultured skin fibroblasts. Using microsatellite DNA markers of chromosome 12p, we detected 3 alleles--including 2 different alleles of maternal origin--in cultured skin fibroblasts, suggesting that the tetrasomy 12p is the result of a prezygotic event, with a nondisjunction event during maternal meiosis.

[Prenatal diagnosis of autosomal recessive polycystic kidney disease]. / Diagnostic prénatal de la polykystose rénale récessive autosomique.

OBJECTIVE: Prenatal ultrasonographic detection of autosomal recessive polycystic kidney disease (ARPKD) is of poor reliability, especially in early pregnancy. Molecular genetics allows earlier diagnosis, from 11 weeks of gestation; however, since only indirect diagnosis is possible--the ARPKD gene being localized on chromosome 6 but not identified--the feasibility of molecular diagnosis requires several conditions: definitive diagnosis in the index case, availability of index case and parents' DNA, genetic informativity of the family at the ARPKD locus. Results and limits of this method are analyzed, using a series of 56 requests for prenatal diagnosis. RESULTS: In eight of the 56 families ARPKD was excluded on the basis of histological (seven cases) and/or genetic (two cases) criteria. Molecular study was impossible in three families due to the lack of index case's DNA, and two other families were non-informative. Among the 43 families in which prenatal diagnosis was feasible, analysis of the haplotype of 35 fetuses issued from 29 families showed that 11 fetuses with the same haplotypes as that of the index case were affected, while 24 were not. No false positive or false negative result was reported. CONCLUSIONS: Early and reliable prenatal diagnosis of recessive polycystic kidney disease is possible in nearly 80% of affected families.

[Preimplantation diagnosis with HLA typing: birth of the first double hope child in France]. / Diagnostic préimplantatoire avec typage HLA : naissance du premier enfant du double espoir en France.

Preimplantation genetic diagnosis (PGD) is authorized in France since 1999. After 10 years, technical results are encouraging. With the development of new technologies, our team is able to diagnosis the large majority of chromosome translocations and 75 monogenic diseases. However, PGD remains limited because of the growing augmentation of demands causing an increasing delay for the first procedure of more than 18 months. Since 2006, 19 couples asked for a PGD with HLA typing. In January 2011, 11 couples have already been included in our PGD program. The birth of the first child after PGD with HLA typing offers new perspectives of treatment for these couples.

Preimplantation genetic diagnosis for autosomal recessive polycystic kidney disease.

Autosomal recessive polycystic kidney disease (ARPKD) is one of the most common hereditary renal cystic diseases, and is caused by mutations in the PKHD1 gene. Due to the poor prognosis, there is a strong demand for prenatal diagnosis. Preimplantation genetic diagnosis (PGD) represents an alternative because it avoids the physical and emotional trauma of a pregnancy termination in the case of an affected fetus. A standardized single-cell diagnostic procedure was developed, based on haplotype analysis, enabling PGD to be offered to couples at risk of transmitting ARPKD. Six linked markers within (D6S1714 and D6S243), or in close proximity to (D6S272, D6S436, KIAA0057, D6S1662) the PKHD1 gene were tested by multiplex nested-polymerase chain reaction (PCR), using a Qiagen multiplex PCR kit. PCR analyses were carried out on 50 single lymphocytes. The amplification rate was excellent (100%), with an allele drop-out (ADO) rate ranging from 0 to 8%. Five PGD cycles were performed and 23 embryos were biopsied and analysed using this test. Transferable embryos were obtained in 4 cycles, resulting in two pregnancies and the birth of a healthy boy. This standardized diagnostic procedure allowed the detection of recombination, contamination, and ADO events, providing high assay accuracy with wide applicability.

Multiple displacement amplification improves PGD for fragile X syndrome.

We report an improvement in the PGD test for fragile X syndrome (FXS). Recently, multiple displacement amplification (MDA) has been reported to yield large amounts of DNA from single cells. Taking into account this technique, we developed a new PGD test for FXS, enabling combined analysis of linked polymorphic markers with the study of the non-expanded CGG repeat. Single cell amplification efficiency was first assessed on single lymphocytes. Amplification rate of the different markers ranged from 85 to 95% with an allele drop-out (ADO) rate comprised between 7 and 34%. Using this test, eight PGD cycles were carried out for six couples, and 37 embryos were analysed after preliminary MDA. Amplification rate was increased by this technique from 41 to 66% so that embryos with no results were rarer (14 versus 45% without MDA). Reliability of the test was considerably improved by combining direct with indirect genetic analysis. Furthermore, in cases of fully expanded alleles too large to be amplified by PCR, this test gives an internal amplification control. Embryonic transfers were carried out in all but one PGD cycles. One biochemical and one clinical pregnancy resulted, and a healthy child was born. This single diagnosis procedure could be suitable to most patients carrying FXS.

Novel CFTR mutations in black cystic fibrosis patients.

Cystic fibrosis (CF) is considered as a rare disease in black Africans. In fact, this disease is likely to be underestimated since clinical features consistent with CF diagnosis are often ascribed to environmental factors such as malnutrition. Very little is known about CFTR mutations in affected patients from Central Africa. We report here four novel mutations, i.e., IVS2 + 28 (intron 2), 459T > A (exon 4), EX17a_EX18del (exons 17-18), and IVS22 + IG > A (intron 22), in such patients. An update of CFTR mutations reported in black patients from various ethnies is included. These data might be helpful for genetic counselling regarding CF in black patients.

First specific preimplantation genetic diagnosis for ornithine transcarbamylase deficiency.

Ornithine transcarbamylase (OTC) deficiency is an X-linked dominant metabolic disorder with partial penetrance in heterozygous females. Affected boys usually die from hyperammonemia in the first few days of life, while clinical expression in carrier females ranges from no symptoms to neonatal death. A young couple whose boy had died of OTC deficiency in the neonatal period was referred to our genetic department for their subsequent pregnancy. The fetus was found to be affected, and after genetic counseling the pregnancy was terminated. Prenatal diagnosis of the third pregnancy identified a heterozygous female, who died after a normal birth at age 11 days from hyperammonemia. After this, the couple asked for preimplantation genetic diagnosis (PGD). We have developed a duplex nested PCR assay allowing the amplification of both the mutation and an informative restriction fragment length polymorphism (RFLP) located in the 3' end of the OTC gene. After nested amplification, allele identification was carried out for both loci by double restriction digestion and electrophoresis gel analysis. The co-amplification of both loci provided a means of detecting potential allele dropout or incomplete digestion. Two PGD cycles were carried out, a total of 14 embryos were analysed and a diagnosis could be obtained in 13/14 embryos. There were four unaffected male embryos, four heterozygous females and four unaffected females; the final embryo was an affected one of undetermined gender. In both cycles, three unaffected embryos could be transferred early on Day 4 post-insemination. The second cycle resulted in the birth of a baby boy devoid of the OTC mutation. This constitutes the first birth following PGD carried out by a French team.

Mutations of the SCO1 gene in mitochondrial cytochrome c oxidase deficiency with neonatal-onset hepatic failure and encephalopathy.

Cytochrome c oxidase (COX) catalyzes both electron transfer from cytochrome c to molecular oxygen and the concomitant vectorial proton pumping across the inner mitochondrial membrane. Studying a large family with multiple cases of neonatal ketoacidotic comas and isolated COX deficiency, we have mapped the disease locus to chromosome 17p13.1, in a region encompassing two candidate genes involved in COX assembly-namely, SCO1 and COX10. Mutation screening revealed compound heterozygosity for SCO1 gene mutations in the patients. The mutated allele, inherited from the father, harbored a 2-bp frameshift deletion (DeltaGA; nt 363-364) resulting in both a premature stop codon and a highly unstable mRNA. The maternally inherited mutation (C520T) changed a highly conserved proline into a leucine in the protein (P174L). This proline, adjacent to the CxxxC copper-binding domain of SCO1, is likely to play a crucial role in the tridimentional structure of the domain. Interestingly, the clinical presentation of SCO1-deficient patients markedly differs from that of patients harboring mutations in other COX assembly and/or maturation genes.

Prenatal diagnosis of sporadic Apert syndrome: a sequential diagnostic approach combining three-dimensional computed tomography and molecular biology.

Apert syndrome is characterized by coronal craniosynostosis, midfacial hypoplasia, symmetrical syndactyly of the hands and feet described as 'mitten-like' with varying degrees of mental retardation. It results from a mutation of the fibroblast growth factor-2 (FGFR2) gene. In the absence of a family history, prenatal diagnosis may be difficult based on sonography alone. We report a case in which the prenatal diagnosis of Apert syndrome was suspected by ultrasonography, established by three-dimensional computed tomography scan (3DTS) and confirmed by the detection of a mutation on amniotic cells. This underscores the usefulness of a sequential diagnostic approach combining 3DTS and molecular biology in cases in which sonography alone is not con- clusive.

Prenatal diagnosis of respiratory chain deficiency by direct mutation screening.

Respiratory chain deficiency (RCD) is responsible for a clinically heterogeneous group of early-onset untreatable disorders. Enzymological prenatal diagnosis (PD) can only be offered to a fraction of families. Moreover, due to the two-fold genetic origin of the respiratory chain (nuclear and mitochondrial DNA) and owing to the large number of nuclear genes involved in the respiratory chain assembly, maintenance and functioning, the identification of the disease causing gene in a given family remains challenging. Here, we report on PD of RCD by direct screening of NDUFV1, SDH-Fp, SCO1 and SURF1 mutations in five unrelated families with complex I, II and IV deficiency, respectively. The identification of the disease-causing gene in a given family with RCD is a major issue to provide both adequate genetic counselling and early, reliable PD.