[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.

[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.

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.

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.

[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.

The RNA-binding properties of SMN: deletion analysis of the zebrafish orthologue defines domains conserved in evolution.

Spinal muscular atrophy (SMA) is a common autosomal recessive disorder that results in the degeneration of spinal motor neurons. SMA is caused by alterations of the survival motor neuron ( SMN ) gene which encodes a novel protein of hitherto unclear function. The SMN protein associates with ribonucleoprotein particles involved in RNA processing and exhibits an RNA-binding capacity. We have isolated the zebrafish Danio rerio and nematode Caenorhabditis elegans orthologues and have found that the RNA-binding capacity is conserved across species. Purified recombinant SMN proteins from both species showed selectivity to poly(G) homopolymer RNA in vitro, similar to that of the human protein. Studying deletions of the zebrafish SMN protein, we defined an RNA-binding element in exon 2a, which is highly conserved across species, and revealed that its binding activity is modulated by protein domains encoded by exon 2b and exon 3. Finally, the deleted recombinant zebrafish protein mimicking an SMA frameshift mutation showed a dramatic change in vitro in the formation of the RNA-protein complexes. These observations indicate that the RNA-binding capacity of SMN is an evolutionarily conserved function and further support the view that defects in RNA metabolism most likely account for the pathogenesis of SMA.

The distribution of SMN protein complex in human fetal tissues and its alteration in spinal muscular atrophy.

Spinal muscular atrophy (SMA) is a common autosomal recessive neuromuscular disorder characterized by degeneration of motor neurons of the spinal cord and muscular atrophy. SMA is caused by alterations to the survival of motor neuron (SMN) gene, the function of which has hitherto been unclear. Here, we present immunoblot analyses showing that normal SMN protein expression undergoes a marked decay in the postnatal period compared with fetal development. Morphological and immunohistochemical analyses of the SMN protein in human fetal tissues showed a general distribution in the cytoplasm, except in muscle cells, where SMN protein was immunolocalized to large cytoplasmic dot-like structures and was tightly associated with membrane-free heavy sedimenting complexes. These cytoplasmic structures were similar in size to gem. The SMN protein was markedly deficient in tissues derived from type I SMA fetuses, including skeletal muscles and, as previously shown, spinal cord. While our data do not help decide whether SMA results from impaired SMN expression in spinal cord, skeletal muscle or both, they suggest a requirement for SMN protein during embryo-fetal development.

Correlation between severity and SMN protein level in spinal muscular atrophy.

Spinal muscular atrophy (SMA) is a common autosomal recessive neuromuscular disorder characterized by degeneration of motor neurons of the spinal cord. Three different forms of childhood SMA have been recognized on the basis of age at onset and clinical course: Werdnig-Hoffmann disease (type-1), the intermediate form (type-II) and Kugelberg-Welander disease (type-III). A gene termed 'survival of motor neuron' (SMN) has been recognized as the disease-causing gene in SMA. SMN encodes a protein located within a novel nuclear structure and interacts with RNA-binding proteins. To elucidate the molecular mechanism underlying the pathogenesis of the disease, we examined the expression of the SMN gene in both controls and SMA patients by western blot and immunohistochemical analyses using antibodies raised against the SMN protein. The present study shows a marked deficiency of the SMN protein in SMA.

cDNA isolation, expression, and chromosomal localization of the mouse survival motor neuron gene (Smn).

Spinal muscular atrophy (SMA) is a frequent autosomal recessive disease in human characterized by degeneration of motor neurons of the spinal cord. The genomic region containing the defective gene (5q13) is particularly unstable and prone to large-scale deletions whose characterization led to the identification of the survival motor neuron (SMN) gene, the SMA determining gene encoding a hitherto unknown protein. As an initial step toward the generation of a murine model for SMA, we identified and characterized a full-length murine Smn cDNA. The coding sequence of the mouse Smn gene was found to be 82% identical, at the amino acid level, with the human SMN coding sequence. The Smn locus was mapped to the segment of mouse chromosome 13 exhibiting conservation of synteny with human chromosome 5q11-q23, which contains the SMN gene. However, no evidence for a duplication of the Smn gene was found in the mouse, suggesting that the duplication reported in human is a recent evolutionary event.

The gene encoding p44, a subunit of the transcription factor TFIIH, is involved in large-scale deletions associated with Werdnig-Hoffmann disease.

Mutations of the survival motor neurone gene (SMN) are associated with spinal muscular atrophy (SMA), a frequent lethal autosomal recessive disorder. In spite of this, no phenotype-genotype correlation was observed, since the SMN gene is lacking in the majority of patients affected with either the severe form (type I) or the milder forms (types II and III). Here, we show that the gene encoding p44, a subunit of the basal transcription factor TFIIH, is duplicated in the SMA region and that the p44 gene products (p44t and p44c) differ by three amino acid changes. Gene analysis of a total of 94 unrelated SMA patients revealed that the p44t gene is involved in large-scale deletions associated with Werdnig-Hoffmann disease (type I). The TFIIH polypeptide composition as well as transcription and DNA repair activities are normal in patients lacking the p44t gene on both mutant chromosomes, suggesting that the p44t gene is not critical for the development of SMA.

Survival motor neuron gene deletion in the arthrogryposis multiplex congenita-spinal muscular atrophy association.

The survival motor neuron (SMN) gene was lacking in 6/12 patients with arthrogryposis multiplex congenita (AMC) associated with spinal muscular atrophy (SMA). Neither point mutation in the SMN gene nor evidence for linkage to chromosome 5q13 were found in the other patients. Hitherto, arthrogryposis was regarded as an exclusion criterion in SMA. Our data strongly suggest that AMC of neurogenic origin is genetically heterogeneous, with a subgroup being allelic to SMA. Absence or interruption of the SMN gene in the AMC-SMA association will make the diagnosis easier and genetic counselling will now become feasible.

Large scale deletions of the 5q13 region are specific to Werdnig-Hoffmann disease.

Spinal muscular atrophy (SMA) is characterised by degeneration of anterior horn cells of the spinal cord and represents the second most common, lethal, autosomal recessive disorder after cystic fibrosis. Based on the criteria of the Internatinal SMA Consortium, childhood SMAs are classified into type I (Werdnig-Hoffmann disease), type II (intermediate form), and type III (Kugelberg-Welander disease). Recently, two genes have been found to be associated with SMA. The survival motor neurone gene (SMN) is an SMA determining gene as it is absent in 98.6% of patients. A second gene, XS2G3, or the highly homologous neuronal apoptosis inhibitory protein gene (NAIP) have been found to be more frequently deleted in type I than in the milder forms (types II and III). We investigated the correlation between the clinical phenotype and the genotype at this loci. A total of 106 patients were classified into type I (44), type II (31), and type III (31) and analysed using SMN, markers C212 and C272, and NAIP mapping upstream and downstream from SMN respectively. The combined analysis of all markers showed a large proportion of type I patients (43%) carried deletions of both SMN and its flanking markers (C212/272) and NAIP exon 5), as compared with none of the patients with type II or III SMA. The presence of large scale deletions involving these loci is specific to Werdnig-Hoffman disease (type I) and allows one to predict the severity of the disease in our series.

Structure and organization of the human survival motor neurone (SMN) gene.

Spinal muscular atrophies (SMA) are characterized by degeneration of the anterior horn cells of the spinal cord and represent the second most common fatal autosomal-recessive disorder after cystic fibrosis. We have previously identified the survival motor neurone gene (SMN), a SMA-determining gene in the 5q13 region encoding a hitherto unknown protein. In this report, we describe the organization and structure of SMN. The gene is approximately equal to 20 kb in length and consists of nine exons. Sequence data of the 5' end of the gene show that the dinucleotide repeat C272 is close to several putative binding sites for transcription factors, which will help to characterize the regulation of the SMN and CBCD541 gene expression. The availability of the human SMN and its highly homologous counterpart (CBCD541) gene structures and exon-intron boundaries will hopefully speed up the characterization of SMN gene mutations in SMA.

Identification and characterization of a spinal muscular atrophy-determining gene.

Spinal muscular atrophy (SMA) is a common fatal autosomal recessive disorder characterized by degeneration of lower motor neurons, leading to progressive paralysis with muscular atrophy. The gene for SMA has been mapped to chromosome 5q13, where large-scale deletions have been reported. We describe here the inverted duplication of a 500 kb element in normal chromosomes and narrow the critical region to 140 kb within the telomeric region. This interval contains a 20 kb gene encoding a novel protein of 294 amino acids. An highly homologous gene is present in the centromeric element of 95% of controls. The telomeric gene is either lacking or interrupted in 226 of 229 patients, and patients retaining this gene (3 of 229) carry either a point mutation (Y272C) or short deletions in the consensus splice sites of introns 6 and 7. These data suggest that this gene, termed the survival motor neuron (SMN) gene, is an SMA-determining gene.

Genetic linkage studies of Machado-Joseph disease with chromosome 14q STRPs in 16 Portuguese-Azorean kindreds.

Machado-Joseph disease (MJD) is a dominant multisystem degeneration found mostly among Azoreans and characterized by the adulthood onset of cerebellar, ocular, pyramidal, extrapyramidal, and/or peripheral signs. MJD has been recorded in many other populations, particularly in the United States and Japan. Using the microsatellite DNA polymorphisms (STRPs) D14S53, D14S55, D14S48, and D14S45, we found significantly positive lod scores in 16 Portuguese kindreds, suggesting that the MJD locus is linked to chromosome 14q in this population. Differences in age-at-onset and many untyped individuals seem to explain the lower lod scores. Using HOMOG, no evidence was found for heterogeneity with the five Japanese families in whom linkage was reported.

De novo and inherited deletions of the 5q13 region in spinal muscular atrophies.

Spinal muscular atrophies (SMAs) represent the second most common fatal autosomal recessive disorder after cystic fibrosis. Childhood spinal muscular atrophies are divided into severe (type I) and mild forms (types II and III). By a combination of genetic and physical mapping, a yeast artificial chromosome contig of the 5q13 region spanning the disease locus was constructed that showed the presence of low copy repeats in this region. Allele segregation was analyzed at the closest genetic loci detected by markers C212 and C272 in 201 SMA families. Inherited and de novo deletions were observed in nine unrelated SMA patients. Moreover, deletions were strongly suggested in at least 18 percent of SMA type I patients by the observation of marked heterozygosity deficiency for the loci studied. These results indicate that deletion events are statistically associated with the severe form of spinal muscular atrophy.