Mosaic complete tetrasomy 21 in a fetus with complete atrioventricular septal defect and minor morphological variations.

BACKGROUND: Tetrasomy 21 is a very rare aneuploidy which could clinically resemble a Down syndrome. It was most often described in its partial form than complete. We report the prenatal, pathological and genetic characteristics of a fetus with mosaic complete tetrasomy 21. This is the second well-documented description of a complete tetrasomy 21 in the literature. METHODS: Prenatal and fetal pathological examinations, cytogenetic and molecular analyses were performed to characterize fetal features with tetrasomy 21. RESULTS: Prenatal ultrasound examination revealed an isolated complete atrioventricular septal defect with normal karyotype on amniotic fluid. After termination of pregnancy, clinical examination of the fetus evoked trisomy 21 or Down syndrome. Chromosomal microarray analysis and FISH on lung tissue showed a mosaicism with four copies of chromosome 21 (tetrasomy 21). CONCLUSION: Our observation and the review of the literature reported the possibility of very weak mosaicism and disease-causing confined tissue-specific mosaicism in fetus or alive patients with chromosome 21 aneuploidy, mainly Down syndrome. In case of clinical diagnosis suggestive of Down syndrome, attention must be paid to the risk of false-negative test due to chromosomal mosaicism (very weak percentage, different tissue distribution). To overcome this risk, it is necessary to privilege the diagnostic techniques without culture step and to increase the number of cells and tissues analyzed, if possible. This study highlights the limits of microarray as the unique diagnostic approach in case of weak mosaic and French cytogenetics guidelines recommend to check anomalies seen in microarray by another technique on the same tissue.

A de novo microdeletion of SEMA5A in a boy with autism spectrum disorder and intellectual disability.

Semaphorins are a large family of secreted and membrane-associated proteins necessary for wiring of the brain. Semaphorin 5A (SEMA5A) acts as a bifunctional guidance cue, exerting both attractive and inhibitory effects on developing axons. Previous studies have suggested that SEMA5A could be a susceptibility gene for autism spectrum disorders (ASDs). We first identified a de novo translocation t(5;22)(p15.3;q11.21) in a patient with ASD and intellectual disability (ID). At the translocation breakpoint on chromosome 5, we observed a 861-kb deletion encompassing the end of the SEMA5A gene. We delineated the breakpoint by NGS and observed that no gene was disrupted on chromosome 22. We then used Sanger sequencing to search for deleterious variants affecting SEMA5A in 142 patients with ASD. We also identified two independent heterozygous variants located in a conserved functional domain of the protein. Both variants were maternally inherited and predicted as deleterious. Our genetic screens identified the first case of a de novo SEMA5A microdeletion in a patient with ASD and ID. Although our study alone cannot formally associate SEMA5A with susceptibility to ASD, it provides additional evidence that Semaphorin dysfunction could lead to ASD and ID. Further studies on Semaphorins are warranted to better understand the role of this family of genes in susceptibility to neurodevelopmental disorders.

6q16.3q23.3 duplication associated with Prader-Willi-like syndrome.

BACKGROUND: Prader-Willi syndrome (PWS) is characterized by hypotonia, delayed neuropsychomotor development, overeating, obesity and mental deficiency. This phenotype is encountered in other conditions, defining Prader-Willi-like syndrome (PWLS). CASE PRESENTATION: We report a 14-year-old boy with a complex small supernumerary marker chromosome (sSMC) associated with PWLS. The propositus presents clinical features commonly found in patients with PWLS, including growth hormone deficit. Banding karyotype analysis and fluorescence in situ hybridization (FISH) revealed a marker derived from chromosome 6 and a neocentromere as suspected, but array-CGH enabled us to characterize this marker as a der(10)t(6;10)(6qter → 6q23.3::10p11.1 → 10p11.21)dn. As far as we know, this is the first diagnosed case of PWLS associated with a complex sSMC, involving a 30.9 Mb gain in the 6q16.3q23.3 region and a 3.5 Mb gain in the 10p11.21p11.1 region. Several genes have been mapped to the 6q region including the TCBA1 gene, which is associated with developmental delay and recurrent infections, the ENPP1 gene, associated with insulin resistance and susceptibility to obesity and the BMIQ3 gene, associated with body mass index (BMI). No OMIM gene was found in the smallest 10p11.21p11.1 region. CONCLUSIONS: We suggest that the duplicated chromosome segment 6q16.3q23.3 may be responsible for the phenotype of our case and may also be a candidate locus of PWLS.

Delineation of the 3p14.1p13 microdeletion associated with syndromic distal limb contractures.

Distal limb contractures (DLC) represent a heterogeneous clinical and genetic condition. Overall, 20-25% of the DLC are caused by mutations in genes encoding the muscle contractile apparatus. Large interstitial deletions of the 3p have already been diagnosed by standard chromosomal analysis, but not associated with a specific phenotype. We report on four patients with syndromic DLC presenting with a de novo 3p14.1p13 microdeletion. The clinical features associated multiple contractures, feeding problems, developmental delay, and intellectual disability. Facial dysmorphism was constant with low-set posteriorly rotated ears and blepharophimosis. Review of previously reported cases with a precise mapping of the deletions, documented a 250 kb smallest region of overlap (SRO) necessary for DLC. This region contained one gene, EIF4E3, the first three exons of the FOXP1 gene, and an intronic enhancer of FOXP1 named hs1149. Sanger sequencing and locus quantification of hs1149, EIF4E3, and FOXP1 in a cohort of 11 French patients affected by DLC appeared normal. In conclusion, we delineate a new microdeletion syndrome involving the 3p14.1p13 locus and associated with DLC and severe developmental delay.

An improved method to extract DNA from 1 ml of uncultured amniotic fluid from patients at less than 16 weeks' gestation.

The aim of this study was to develop an improved technique for DNA extraction from 1 ml of uncultured AF from patients with a gestational age less than 16 weeks and to allow the use of array-CGH without DNA amplification. The DNA extraction protocol was tested in a series of 90 samples including 41 of uncultured AF at less than 16 weeks of gestation. Statistical analyses were performed using linear regression. To evaluate the sensitivity and the specificity of array-CGH on 1 ml of uncultured AF, five samples with an abnormal karyotype (three with aneuploidy, two with structural abnormalities) and five with a normal karyotype were studied. This protocol was reproducible and we were able to show a great improvement with higher yield of DNA obtained from all patients, including those with a gestational age less than 16 weeks (p = 0.003). All chromosomal abnormalities were detected and characterized by array-CGH and normal samples showed normal profiles. This new DNA extraction protocol associated with array-CGH analysis could be used in prenatal testing even when gestational age is less than 16 weeks, especially in cases with abnormal ultrasound findings.

The DYRK1A gene is a cause of syndromic intellectual disability with severe microcephaly and epilepsy.

BACKGROUND: DYRK1A plays different functions during development, with an important role in controlling brain growth through neuronal proliferation and neurogenesis. It is expressed in a gene dosage dependent manner since dyrk1a haploinsufficiency induces a reduced brain size in mice, and DYRK1A overexpression is the candidate gene for intellectual disability (ID) and microcephaly in Down syndrome. We have identified a 69 kb deletion including the 5' region of the DYRK1A gene in a patient with growth retardation, primary microcephaly, facial dysmorphism, seizures, ataxic gait, absent speech and ID. Because four patients previously reported with intragenic DYRK1A rearrangements or 21q22 microdeletions including only DYRK1A presented with overlapping phenotypes, we hypothesised that DYRK1A mutations could be responsible for syndromic ID with severe microcephaly and epilepsy. METHODS: The DYRK1A gene was studied by direct sequencing and quantitative PCR in a cohort of 105 patients with ID and at least two symptoms from the Angelman syndrome spectrum (microcephaly < -2.5 SD, ataxic gait, seizures and speech delay). RESULTS: We identified a de novo frameshift mutation (c.290_291delCT; p.Ser97Cysfs*98) in a patient with growth retardation, primary severe microcephaly, delayed language, ID, and seizures. CONCLUSION: The identification of a truncating mutation in a patient with ID, severe microcephaly, epilepsy, and growth retardation, combined with its dual function in regulating the neural proliferation/neuronal differentiation, adds DYRK1A to the list of genes responsible for such a phenotype. ID, microcephaly, epilepsy, and language delay are the more specific features associated with DYRK1A abnormalities. DYRK1A studies should be discussed in patients presenting such a phenotype.

17q21.31 microdeletion in a patient with pituitary stalk interruption syndrome.

We report the case of a 26-month-old boy with mental retardation, facial dysmorphism, childhood feeding difficulties, short stature, bilateral cryptorchidism, micropenis, and heart defect. Endocrinal evaluation revealed complete growth hormone deficiency (GHD) and gonadotropic deficiency, and pituitary magnetic resonance imaging showed partial pituitary stalk interruption syndrome (PSIS). A de novo 493 kb microdeletion on chromosome 17q21.31 was identified using array comparative genomic hybridization (array-CGH) analysis. This is the first report of PSIS in the phenotypical spectrum of 17q21.31 microdeletion syndrome, although other midline abnormalities have previously been described. Our report suggests that GHD should be investigated in patients with 17q21.31 microdeletion syndrome and short stature, defined by a body height below - 2 standard deviation scores (SDS) for age and sex. This finding also opens new avenues of research on the etiopathogenesis of PSIS, for which the genetic mechanisms remain unknown.