Sophie Brisset

Terminal 14q32.33 deletion: Genotype–phenotype correlation†

We report on a female infant presenting with psychomotor retardation and facial dysmorphism. Cytogenetic studies showed an abnormal chromosome 14 with ectopic NOR sequences at the extremity of the long arm with a terminal 14q32.33 deletion. Review of the eight cases with pure terminal 14q32.3 deletions described to date documented that our observation is the smallest terminal 14q deletion ever reported. Thus, genotype–phenotype correlation allows us to delimit the critical region for mental retardation, hypotonia, epi‐telecanthus, short bulbous nose, long philtrum, thin upper lip, and small mouth observed in 14 qter deletions to the subtelomeric 1.6 Mb of chromosome 14.

Genotype-phenotype correlation in 13q13.3-q21.3 deletion.

Pure interstitial deletions of the long arm of chromosome 13 are correlated with variable phenotypes according to the size and the location of the deleted region. Deletions involving the 13q13q21 region are rare. In order to establish interstitial 13q genotype-phenotype correlation, we used high resolution 244K oligonucleotide array in addition to conventional karyotype and molecular (fluorescent in situ hybridization, microsatellite markers analysis) techniques in two independent probands carrying a deletion 13q13 to 13q21. First patient was a 3-year-old girl with mental retardation and dysmorphy carrying a 13q13.3q21.31 de novo deletion diagnosed post-natally. The second one was a fetus with de novo del(13)(q14q21.2) associated with first trimester increased nuchal translucency. We showed that specific dysmorphic features (macrocephaly, high forehead, hypertelorism, large nose, large and malformed ears and retrognathia) were correlated to the common 13q14q21 chromosomal segment. Physical examination revealed overgrowth with global measurement up to the 95th percentile in both probands. This is the second description of overgrowth in patients carrying a 13q deletion. Haploinsufficiency of common candidates genes such as CKAP2, SUGT1, LECT1, DCLK1 and SMAD9, involved in cell division and bone development, is a possible mechanism that could explain overgrowth in both patients. This study underlines also that cytogenetic analysis could be performed in patients with overgrowth.

Pure and complete trisomy 18p due to a supernumerary marker chromosome associated with moderate mental retardation

Trisomy for the short arm of chromosome 18 or trisomy 18p, is rarely described. We report on a 13‐year‐old boy with minor facial anomalies, mental retardation, bilateral cryptorchidism associated with a de novo supernumerary marker chromosome (SMC). Using fluorescence in situ hybridization and comparative genomic hybridization analyses, this SMC corresponded to the p arm of chromosome 18 associated with a centromere of either chromosome 13 or 21 and nucleolus organizing regions (NORs). We report here the first case of a pure and complete trisomy 18p due to a SMC. This report and review of literature confirm that the main phenotypic anomaly associated with trisomy 18p is moderate mental retardation.

Molecular cytogenetic characterization of a 4p15.1-pter duplication and a 4q35.1-qter deletion in a recombinant of chromosome 4 pericentric inversion†

To date, 10 cases of recombinant of chromosome 4 pericentric inversion involving sub‐bands p14p15 and q35 have been described. We report on the first case analyzed using array‐CGH in a female infant presenting psychomotor and growth retardation, facial anomalies, axial hypotonia, short neck, wide spaced nipples and cardiac defects. Conventional karyotype associated to FISH revealed a recombinant chromosome 4 with partial 4p duplication and 4q deletion derived from a paternal pericentric inversion. Array‐CGH allowed us to precise rec4 breakpoints: the proposita carried a small 4.82–4.97 Mb 4q35.1 terminal deletion and a large 35.3–36.7 Mb 4p15.1 terminal duplication. Duplications of the distal 2/3 of short arm of chromosome 4 give rise to recognizable craniofacial features but no specific visceral malformation. A contrario small terminal 4q deletions are associated with cardiac defects. This case and review of literature suggest that two genes ArgBP2 and PDLIM3, located at 4q35.1 and both involved in cardiac and muscle development, could be responsible for cardiac defects observed in terminal 4q35.1 deletions.

Tetrasomy 13q31.1qter due to an inverted duplicated neocentric marker chromosome in a fetus with multiple malformations

Small supernumerary marker chromosome (sSMC) lacking alpha satellite DNA or endogenous centromere regions are rare and contain fully functional centromeres, called neocentromeres. We report on a woman with a 14‐week gestation pregnancy with a cystic hygroma and cerebellar hypoplasia at ultrasound examination. Cytogenetic studies showed a karyotype 47,XY,+mar dn. This sSMC was observed in chorionic villi, lung, and muscle tissue. Array Comparative Genomic Hybridization showed a gain from 13q31.1 to 13qter region. Fluorescent in situ hybridization with pan alpha satellite probe and probes specific for chromosome 13 showed a marker corresponding to an inversion duplication of the 13q distal chromosomal region without alpha satellite DNA sequence, suggesting the presence of a neocentromere. Examination of the fetus showed dysmorphic features, cystic cervical hygroma, postaxial polydactyly of the right hand and left foot with short fingers, malrotation of the gut, and a micropenis with hypospadias. Genotype–phenotype correlation in tetrasomy 13q is discussed according to the four 13q chromosomal breakpoints reported (13q32, 13q31, 13q21, 13q14) for chromosome 13 supernumerary markers.

Small supernumerary marker chromosomes derived from chromosomes 6 and 20 in a woman with recurrent spontaneous abortions

In this report, we describe a case of multiple small supernumerary marker chromosomes (sSMC) presenting with recurrent abortions. Peripheral blood lymphocytes of a young, healthy and non-consanguineous couple who asked for genetic evaluation after two spontaneous miscarriages were obtained for karyotypes. Lymphocytes of the woman were analyzed by FISH techniques and DNA was extracted and used for array CGH investigation. Karyotyping revealed 48,XX,+2mar[24]/47,XX,+mar[5]/46,XX[3] for the woman and 46,XY for her husband. FISH analysis showed that the two sSMC consisted of chromosomes 6 and 20. Array CGH analysis showed gains of the 6p11.2q12 (9 Mb) and 20 p11.21 (3.3 Mb) chromosomal regions with a total of 42 genes present on both sSMC. Our findings support also the hypothesis that the modification of the expression of some genes involved in embryo implantation, like THBD gene, could be responsible in the recurrent abortions. This report underpins the necessity of array CGH for characterizing precisely sSMC and helping in genotype-phenotype correlations. Furthermore, a literature review on sSMC is included.

First prenatal case of proximal 19p13.12 microdeletion syndrome: New insights and new delineation of the syndrome

Proximal 19p13.12 microdeletion has been rarely reported. Only five postnatal cases with intellectual disability, facial dysmorphism, branchial arch defects and overlapping deletions involving proximal 19p13.12 have been documented. Two critical intervals were previously defined: a 700 kb for branchial arch defects and a 350 kb for hypertrichosis-synophrys-protruding front teeth. We describe the first prenatal case, a fetal death in utero at 39 weeks of gestation. Agilent 180K array-CGH analysis identified a heterozygous interstitial 745 kb deletion at 19p13.12 chromosome region, encompassing both previously reported critical intervals, including at least 6 functionally relevant genes: NOTCH3, SYDE1, AKAP8, AKAP8L, WIZ and BRD4. Quantitative PCR showed that the deletion occurred de novo with a median size of 753 kb. NOTCH3 and SYDE1 were candidate genes for placental pathology whilst AKAP8, AKAP8L, WIZ and BRD4 were highly expressed in the branchial arches. Molecular characterization and sequencing of candidate genes for placental pathology and branchial arch defects were carried out in order to correlate the genotype-phenotype relationship and unravel the underlying mechanism of proximal 19p13.12 microdeletion syndrome. This case also contributes to define the novel critical interval and expand the clinical phenotype spectrum of proximal 19p13.12 microdeletion syndrome.