Molecular characterization of 39 de novo sSMC: contribution to prognosis and genetic counselling, a prospective study.

Small supernumerary marker chromosomes (sSMCs) are structurally abnormal chromosomes that cannot be characterized by karyotype. In many prenatal cases of de novo sSMC, the outcome of pregnancy is difficult to predict because the euchromatin content is unclear. This study aimed to determine the presence or absence of euchromatin material of 39 de novo prenatally ascertained sSMC by array-comparative genomic hybridization (array-CGH) or single nucleotide polymorphism (SNP) array. Cases were prospectively ascertained from the study of 65,000 prenatal samples [0.060%; 95% confidence interval (CI), 0.042-0.082]. Array-CGH showed that 22 markers were derived from non-acrocentric markers (56.4%) and 7 from acrocentic markers (18%). The 10 additional cases remained unidentified (25.6%), but 7 of 10 could be further identified using fluorescence in situ hybridization; 69% of de novo sSMC contained euchromatin material, 95.4% of which for non-acrocentric markers. Some sSMC containing euchromatin had a normal phenotype (31% for non-acrocentric and 75% for acrocentric markers). Statistical differences between normal and abnormal phenotypes were shown for the size of the euchromatin material (more or less than 1 Mb, p = 0.0006) and number of genes (more or less than 10, p = 0.0009). This study is the largest to date and shows the utility of array-CGH or SNP array in the detection and characterization of de novo sSMC in a prenatal context.

Recurrent neural tube defects associated with partial trisomy 2p22-pter: report of two siblings and review of the literature.

We report on two male siblings with partial trisomy 2p22-pter and partial monosomy 15q26-qter resulting from a maternally derived translocation t(2;15)(p22;q26). Both fetuses had different neural tube defects (craniorachischisis in the first fetus and anencephaly in the second fetus) which were detected by sonographic examination at the end of the first trimester of pregnancy. This report demonstrates the importance of chromosomal analysis in the etiologic exploration of neural tube defects and supports the importance of 2p24 triplication in neural tube development.

Prenatal diagnosis of a true fetal tetraploidy in direct and cultured chorionic villi.

Prenatal diagnosis of a true fetal tetraploidy in direct and cultured chorionic villi: Tetraploidy is characterized by four complete sets of chromosomes (4n= 92). Although it has been frequently reported in spontaneous abortions, tetraploidy is extremely rare in term pregnancy. Most of late surviving patients are diploid/tetraploid mosaics and present severe mental and physical impairment. Up to date, only five tetraploidies were ascertained in the prenatal stage in amniocytes and/or fetal blood lymphocytes. No one has been reported in chorionic villi probably because tetraploidy is generally considered in this tissue as a false positive result due to confined placental mosaicism (CPM) or placental culture artefacts. We report here on a case of tetraploidy detected in chorionic villi because of fetal cystic hygroma. We discuss the reliability of this diagnosis and propose guidelines in the follow-up of tetraploidies detected after chorionic villus sampling (CVS). Thus a misdiagnosis of this poor condition will be avoided at best and an appropriate genetic counseling will be given to the parents.

[Epidemiology of orofacial clefts (1995-2006) in France (Congenital Malformations of Alsace Registry)]. / Épidémiologie des fentes labio-palatines : expérience du Registre de malformations congénitales d'Alsace entre 1995 et 2006.

OBJECTIVES: To review clinical and epidemiologic data of orofacial clefts and to evaluate the efficacy and the impact of prenatal diagnosis. MATERIAL AND METHODS: A population-based retrospective study was carried out on data from the Congenital Malformations of Alsace Registry (France) between 1995 and 2006. RESULTS: A total of 321 orofacial clefts were recorded (overall prevalence, 2.1 per 1000), divided into cleft lip (CL) or cleft lip palate (CLP) (204 cases) and cleft palate (117 cases). The cleft lip and cleft lip palate CL±P sex-ratio was 1.87, whereas the CP sex-ratio was 1. CLs were more often unilateral than CLPs (79% versus 59%). CLs were unilateral in 79% of the cases (60/76), bilateral in 20% of the cases (15/76), and median in 1% (1/76); 55% of the unilateral CLs were right and 45% were left. CLPs were unilateral in 59% of the cases (76/128), bilateral in 39% of the cases (50/128), and median in 2% (2/128); 45% of the unilateral CLPs were right and 55% were left. The 117 CPs were divided into 50 clefts of the total palate (43%) and 67 clefts of the posterior palate (57%); 25 cases (21%) of Pierre Robin sequence were collected. Sixty-six percent of CL±P (134/204) were associated with other congenital anomalies, including chromosome abnormality in 31 cases and identified monogenic syndrome or association in 12 cases. The most frequent chromosome abnormalities were 16 cases of trisomy 13 and 7 cases of trisomy 18. No cases of 22q11.2 microdeletion or duplication were detected among CL±P. Monogenic syndromes were identified in 6% (12/204) of CL±P cases: Van der Woude syndrome (2 cases); CHARGE syndrome (2 cases); ectrodactyly, ectodermal dysplasia, and cleft/lip palate (EEC) syndrome (2 cases); branchiooculofacial (BOF) syndrome (1 case); Treacher-Collins syndrome (1 case); Nager syndrome (1 case); Goldenhar syndrome (1 case); holoprosencephaly spectrum (1 case); and Meckel syndrome (1 case). Forty-two percent of CPs (49/117) were associated with other congenital anomalies; chromosome abnormality was identified in 12 cases and monogenic syndrome was diagnosed in 14 cases. The most frequent chromosome abnormality was 22q11 microdeletion (5 cases). Monogenic syndromes were recognized in 12% of the CP cases (14/117): fragile X syndrome (2 cases), Meckel syndrome (2 cases), Orofaciodigital syndrome type I (OFD1) (1 case), Stickler syndrome (1 case), Larsen syndrome (1 case), Kniest syndrome (1 case), Cornelia de Lange syndrome (1 case), thanatophoric dysplasia (1 case), other unknown bone chondrodysplasia (1 case), Fryns syndrome (1 case), fetal akinesia sequence (1 case), and Silver-Russel syndrome (1 case). Fifty-two percent of CL cases (106/204) were prenatally diagnosed. An increasing tendency was observed between the 1995-2000 and 2001-2006 periods with a detection rate increasing from 47% to 56%. During the whole period, only 1 case of CP was prenatally diagnosed. Eighty-two percent of all cases (263/321) were livebirths; 8 stillbirths were reported (2%); 50 syndromic or associated cases (16%) led to medical abortion (no termination of pregnancy was performed for isolated cleft). CONCLUSION: Orofacial clefts are a frequent malformation with a total prevalence of 2.1 per 1000 total births. Sonbographic prenatal diagnosis of orofacial clefts remains difficult with a mean detection rate about 50% for CL±P and is extremely rare for CP. Associated malformations and genetic syndromes are frequent and require a systematic survey. This study also highlights the different pathogenic background of CL±P compared to CP, regarding the sex-ratio and the proportion and type of associated malformations.

Phenotype in X chromosome rearrangements: pitfalls of X inactivation study.

OBJECTIVE: X inactivation pattern in X chromosome rearrangements usually favor the less unbalanced cells. It is correlated to a normal phenotype, small size or infertility. We studied the correlation between phenotype and X inactivation ratio in patients with X structural anomalies. PATIENTS AND METHODS: During the 1999-2005 period, 12 X chromosome rearrangements, including three prenatal cases, were diagnosed in the Laboratoire de Cytogénétique of Strasbourg. In seven cases, X inactivation ratio could be assessed by late replication or methylation assay. RESULTS: In three of seven cases (del Xp, dup Xp, t(X;A)), X inactivation ratio and phenotype were consistent. The four other cases showed discrepancies between phenotype and X inactivation pattern: mental retardation and dysmorphism in a case of balanced X-autosome translocation, schizophrenia and autism in two cases of XX maleness and MLS syndrome (microphthalmia with linear skin defects) in a case of Xp(21.3-pter) deletion. CONCLUSION: Discrepancies between X inactivation ratio and phenotype are not rare and can be due to gene disruption, position effect, complex microrearrangements, variable pattern of X inactivation in different tissues or fortuitous association. In this context, the prognostic value of X inactivation study in prenatal diagnosis will be discussed.