Molecular and clinical delineation of 2p15p16.1 microdeletion syndrome

Interstitial 2p15p16.1 microdeletion is a rare chromosomal syndrome previously reported in 33 patients. It is characterized by intellectual disability, developmental delay, autism spectrum disorders, microcephaly, short stature, dysmorphic features, and multiple congenital organ defects. It is defined as a contiguous gene syndrome and two critical regions have been proposed at 2p15 and 2p16.1 loci. Nevertheless, patients with deletion of both critical regions shared similar features of the phenotype and the correlation genotype-phenotype is still unclear. We review all published cases and describe three additional patients, to define the phenotype-genotype correlation more precisely. We reported on two patients including the first prenatal case described so far, carrying a 2p15 deletion affecting two genes: XPO1 and part of USP34. Both patients shared similar features including facial dysmorphism and cerebral abnormalities. We considered the genes involved in the deleted segment to further understand the abnormal phenotype. The third case we described here was a 4-year-old boy with a heterozygous de novo 427 kb deletion encompassing BCL11A and PAPOLG at 2p16.1. He displayed speech delay, autistic traits, and motor stereotypies associated with brain structure abnormalities. We discuss the contribution of the genes included in the deletion to the abnormal phenotype. Our three new patients compared to previous cases, highlighted that despite two critical regions, both distal deletion at 2p16.1 and proximal deletion at 2p15 are associated with phenotypes that are very close to each other. Finally, we also discuss the genetic counseling of this microdeletion syndrome particularly in the course of prenatal diagnosis.

[Autism spectrum disorders: heterogeneous genetic etiologies]

Autism spectrum disorders: heterogeneous genetic etiologies. Autism Spectrum Disorders (ASD) are neurodevelopmental diseases affecting around 1% of the general population. Symptoms appear early in the development, usually before 3 years of life. Clinical features are extremely heterogeneous as genetic etiologies that underlie ASD. Genetic findings are present in 25% of ASD patients especially in specific cellular pathways as neurodevelopment or synapse architecture. ASD appears to be the combination of several de novo or/and inherited deleterious genetic variants. Here we propose to discuss genetic findings in these disorders and see how genetic research is able to give new treatment for ASD.

Insertion of an extra copy of Xq22.2 into 1p36 results in functional duplication of the PLP1 gene in a girl with classical Pelizaeus-Merzbacher disease

Background

Pelizaeus-Merzbacher disease (PMD) is an X-linked dysmyelinating disorder characterized by nystagmus, hypotonia, ataxia, progressive spasticity, and cognitive decline. PMD classically results from a duplication of a genomic segment encompassing the entire PLP1 gene. Since the PLP1 gene is located in Xq22, PMD affects mostly boys.

Methods and results

Here we report the case of a girl with typical PMD. Copy number analysis of the PLP1 locus revealed a duplication of the entire gene and FISH analysis showed that the extra copy of the PLP1 gene was actually inserted in chromosome 1p36. This insertion of an additional copy of PLP1 in an autosome led to a functional duplication irrespective of the X-inactivation pattern. Subsequent overexpression of PLP1 was the cause of the PMD phenotype observed in this girl. Further sequencing of the breakpoint junction revealed a microhomology and thus suggested a replication based mechanism (such as FoSTeS or MMBIR).

Conclusion

This case emphasizes the susceptibility of the PLP1 locus to complex rearrangement likely driven by the Xq22 local genomic architecture. In addition, careful consideration should be given to girls with classical PMD clinical features since they usually experience complex PLP1 genomic alteration with a distinct risk of inheritance.

Clinical and molecular delineation of Tetrasomy 9p syndrome: report of 12 new cases and literature review

Tetrasomy 9p is a generic term describing the presence of a supernumerary chromosome incorporating two copies of the 9p arm. Two varieties exist: isodicentric chromosome 9p (i(9p)), where the two 9p arms are linked by a single centromeric region, and pseudodicentric 9p (idic(9p)), where one active and one inactive centromere are linked together by a proximal segment of 9q that may incorporate euchromatic material. In living patients, i(9p) and idic(9p) are usually present in a mosaic state. Fifty-four cases, including fetuses, have been reported, of which only two have been molecularly characterized using array-CGH. Tetrasomy 9p leads to a variable phenotype ranging from multiple congenital anomalies with severe intellectual disability and growth delay to subnormal cognitive and physical developments. Hypertelorism, abnormal ears, microretrognathia and bulbous nose are the most common dysmorphic traits. Microcephaly, growth retardation, joint dislocation, scoliosis, cardiac and renal anomalies were reported in several cases. Those physical anomalies are often, but not universally, accompanied by intellectual disability. The most recurrent breakpoints, defined by conventional cytogenetics, are 9p10, 9q12 and 9q13. We report on 12 new patients with tetrasomy 9p (3 i(9p), 8 idic(9p) and one structurally uncharacterized), including the first case of parental germline mosaicism. All rearrangements have been characterized by DNA microarray. Based on our results and a review of the literature, we further delineate the prenatal and postnatal clinical spectrum of this imbalance. Our results show poor genotype-phenotype correlations and underline the need of precise molecular characterization of the supernumerary marker.

Complex nature of apparently balanced chromosomal rearrangements in patients with autism spectrum disorder

Background

Apparently balanced chromosomal rearrangements can be associated with an abnormal phenotype, including intellectual disability and autism spectrum disorder (ASD). Genome-wide microarrays reveal cryptic genomic imbalances, related or not to the breakpoints, in 25% to 50% of patients with an abnormal phenotype carrying a microscopically balanced chromosomal rearrangement. Here we performed microarray analysis of 18 patients with ASD carrying balanced chromosomal abnormalities to identify submicroscopic imbalances implicated in abnormal neurodevelopment.

Methods

Eighteen patients with ASD carrying apparently balanced chromosomal abnormalities were screened using single nucleotide polymorphism (SNP) arrays. Nine rearrangements were de novo, seven inherited, and two of unknown inheritance. Genomic imbalances were confirmed by fluorescence in situ hybridization and quantitative PCR.

Results

We detected clinically significant de novo copy number variants in four patients (22%), including three with de novo rearrangements and one with an inherited abnormality. The sizes ranged from 3.3 to 4.9 Mb; three were related to the breakpoint regions and one occurred elsewhere. We report a patient with a duplication of the Wolf-Hirschhorn syndrome critical region, contributing to the delineation of this rare genomic disorder. The patient has a chromosome 4p inverted duplication deletion, with a 0.5 Mb deletion of terminal 4p and a 4.2 Mb duplication of 4p16.2p16.3. The other cases included an apparently balanced de novo translocation t(5;18)(q12;p11.2) with a 4.2 Mb deletion at the 18p breakpoint, a subject with de novo pericentric inversion inv(11)(p14q23.2) in whom the array revealed a de novo 4.9 Mb deletion in 7q21.3q22.1, and a patient with a maternal inv(2)(q14.2q37.3) with a de novo 3.3 Mb terminal 2q deletion and a 4.2 Mb duplication at the proximal breakpoint. In addition, we identified a rare de novo deletion of unknown significance on a chromosome unrelated to the initial rearrangement, disrupting a single gene, RFX3.

Conclusions

These findings underscore the utility of SNP arrays for investigating apparently balanced chromosomal abnormalities in subjects with ASD or related neurodevelopmental disorders in both clinical and research settings.

3D-FISH analysis reveals chromatid cohesion defect during interphase in Roberts syndrome

Background

Roberts syndrome (RBS) is a rare autosomal recessive disorder mainly characterized by growth retardation, limb defects and craniofacial anomalies. Characteristic cytogenetic findings are “railroad track” appearance of chromatids and premature centromere separation in metaphase spreads. Mutations in the ESCO2 (establishment of cohesion 1 homolog 2) gene located in 8p21.1 have been found in several families. ESCO2, a member of the cohesion establishing complex, has a role in the effective cohesion between sister chromatids. In order to analyze sister chromatids topography during interphase, we performed 3D-FISH using pericentromeric heterochromatin probes of chromosomes 1, 4, 9 and 16, on preserved nuclei from a fetus with RBS carrying compound heterozygous null mutations in the ESCO2 gene.

Results

Along with the first observation of an abnormal separation between sister chromatids in heterochromatic regions, we observed a statistically significant change in the intranuclear localization of pericentromeric heterochromatin of chromosome 1 in cells of the fetus compared to normal cells, demonstrating for the first time a modification in the spatial arrangement of chromosome domains during interphase.

Conclusion

We hypothesize that the disorganization of nuclear architecture may result in multiple gene deregulations, either through disruption of DNA cis interaction –such as modification of chromatin loop formation and gene insulation - mediated by cohesin complex, or by relocation of chromosome territories. These changes may modify interactions between the chromatin and the proteins associated with the inner nuclear membrane or the pore complexes. This model offers a link between the molecular defect in cohesion and the complex phenotypic anomalies observed in RBS.

Electronic supplementary material

The online version of this article (doi:10.1186/s13039-014-0059-6) contains supplementary material, which is available to authorized users.

Prenatal diagnosis of 24 cases of microduplication 22q11.2: an investigation of phenotype-genotype correlations

OBJECTIVE

Microduplication 22q11.2 is primarily characterized by a highly variable clinical phenotype, which ranges from apparently normal or slightly dysmorphic features (in the presence or absence of learning disorders) to severe malformations with profound mental retardation. Hence, genetic counseling is particularly challenging when microduplication 22q11.2 is identified in a prenatal diagnosis. Here, we report on 24 prenatal cases of microduplication 22q11.2.

METHODS

Seventeen of the cases were also reanalyzed by microarray analysis, in order to determine copy number variations (CNVs, which are thought to influence expressivity). We also searched for possible correlations between fetal phenotypes, indications for invasive prenatal diagnosis, inheritance, and pregnancy outcomes.

RESULTS

Of the 24 cases, 15 were inherited, six occurred de novo, and three were of unknown origin. Termination of pregnancy occurred in seven cases and was mainly decided on the basis of ultrasound findings. Moreover, additional CNVs were found in some patients and we try to make a genotype-phenotype correlation.

CONCLUSION

We discuss the complexity of genetic counseling for microduplication 22q11.2 and comment on possible explanations for the clinical heterogeneity of this syndrome. In particular, we assessed the co-existence of additional CNVs and their contribution to phenotypic variations in chromosome 22q11.2 microduplication syndrome.

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.

Parental origin of the X-chromosome does not influence growth hormone treatment effect in Turner syndrome

CONTEXT

The parental origin of the intact X-chromosome has been reported to affect phenotype and response to GH treatment in Turner syndrome (TS).

OBJECTIVE

Our objective was to evaluate the influence of the parental origin of the X-chromosome on body growth and GH treatment effect in TS.

DESIGN AND SETTING

We conducted a population-based cohort study of TS patients previously treated with GH.

PARTICIPANTS

Participants included patients with a nonmosaic 45,X karyotype; 556 women were identified as eligible, 233 (49%) of whom participated, together with their mothers. Data were analyzed for 180 of these patients.

MAIN OUTCOME MEASURES

We performed fluorescence in situ hybridization analysis to exclude mosaicism and microsatellite analysis of nine polymorphic markers in DNA from the patients and their mothers. The influence on growth and effect of GH were analyzed by univariate and multivariate methods.

RESULTS

The X-chromosome was of paternal origin (X(pat)) in 52 (29%) of 180 and of maternal origin (X(mat)) in 128 (71%) of 180 patients. Height gain from the start of GH treatment to adult height was similar in X(mat) and X(pat) patients (+2.1 ± 0.9 vs. +2.2 ± 0.8 TS sd score, P = 0.45). The lack of influence of parental origin of the X-chromosome was confirmed in multivariate analysis. Parental origin of the X-chromosome also had no effect on the other growth characteristics studied, including growth velocity during the first year on GH treatment. Patient height was correlated with the heights of both parents and was not influenced by the parental origin of the X-chromosome.

CONCLUSION

In this, the largest such study carried out to date, the parental origin of the X-chromosome did not alter the effect of GH treatment or affect any other features of growth in TS.

Autistic disorder in patients with Williams-Beuren syndrome: a reconsideration of the Williams-Beuren syndrome phenotype

BACKGROUND

Williams-Beuren syndrome (WBS), a rare developmental disorder caused by deletion of contiguous genes at 7q11.23, has been characterized by strengths in socialization (overfriendliness) and communication (excessive talkativeness). WBS has been often considered as the polar opposite behavioral phenotype to autism. Our objective was to better understand the range of phenotypic expression in WBS and the relationship between WBS and autistic disorder.

METHODOLOGY

The study was conducted on 9 French individuals aged from 4 to 37 years old with autistic disorder associated with WBS. Behavioral assessments were performed using Autism Diagnostic Interview-Revised (ADI-R) and Autism Diagnostic Observation Schedule (ADOS) scales. Molecular characterization of the WBS critical region was performed by FISH.

FINDINGS

FISH analysis indicated that all 9 patients displayed the common WBS deletion. All 9 patients met ADI-R and ADOS diagnostic criteria for autism, displaying stereotypies and severe impairments in social interaction and communication (including the absence of expressive language). Additionally, patients showed improvement in social communication over time.

CONCLUSIONS

The results indicate that comorbid autism and WBS is more frequent than expected and suggest that the common WBS deletion can result in a continuum of social communication impairment, ranging from excessive talkativeness and overfriendliness to absence of verbal language and poor social relationships. Appreciation of the possible co-occurrence of WBS and autism challenges the common view that WBS represents the opposite behavioral phenotype of autism, and might lead to improved recognition of WBS in individuals diagnosed with autism.

Genomic imbalances detected by array-CGH in patients with syndromal ocular developmental anomalies

In 65 patients, who had unexplained ocular developmental anomalies (ODAs) with at least one other birth defect and/or intellectual disability, we performed oligonucleotide comparative genome hybridisation-based microarray analysis (array-CGH; 105A or 180K, Agilent Technologies). In four patients, array-CGH identified clinically relevant deletions encompassing a gene known to be involved in ocular development (FOXC1 or OTX2). In four other patients, we found three pathogenic deletions not classically associated with abnormal ocular morphogenesis, namely, del(17)(p13.3p13.3), del(10)(p14p15.3), and del(16)(p11.2p11.2). We also detected copy number variations of uncertain pathogenicity in two other patients. Rearranged segments ranged in size from 0.04 to 5.68 Mb. These results show that array-CGH provides a high diagnostic yield (15%) in patients with syndromal ODAs and can identify previously unknown chromosomal regions associated with these conditions. In addition to their importance for diagnosis and genetic counselling, these data may help identify genes involved in ocular development.

Autism multiplex family with 16p11.2p12.2 microduplication syndrome in monozygotic twins and distal 16p11.2 deletion in their brother

The pericentromeric region of chromosome 16p is rich in segmental duplications that predispose to rearrangements through non-allelic homologous recombination. Several recurrent copy number variations have been described recently in chromosome 16p. 16p11.2 rearrangements (29.5-30.1 Mb) are associated with autism, intellectual disability (ID) and other neurodevelopmental disorders. Another recognizable but less common microdeletion syndrome in 16p11.2p12.2 (21.4 to 28.5-30.1 Mb) has been described in six individuals with ID, whereas apparently reciprocal duplications, studied by standard cytogenetic and fluorescence in situ hybridization techniques, have been reported in three patients with autism spectrum disorders. Here, we report a multiplex family with three boys affected with autism, including two monozygotic twins carrying a de novo 16p11.2p12.2 duplication of 8.95 Mb (21.28-30.23 Mb) characterized by single-nucleotide polymorphism array, encompassing both the 16p11.2 and 16p11.2p12.2 regions. The twins exhibited autism, severe ID, and dysmorphic features, including a triangular face, deep-set eyes, large and prominent nasal bridge, and tall, slender build. The eldest brother presented with autism, mild ID, early-onset obesity and normal craniofacial features, and carried a smaller, overlapping 16p11.2 microdeletion of 847 kb (28.40-29.25 Mb), inherited from his apparently healthy father. Recurrent deletions in this region encompassing the SH2B1 gene were recently reported in early-onset obesity and in individuals with neurodevelopmental disorders associated with phenotypic variability. We discuss the clinical and genetic implications of two different 16p chromosomal rearrangements in this family, and suggest that the 16p11.2 deletion in the father predisposed to the formation of the duplication in his twin children.

Paracentric inversion of chromosome 2 associated with cryptic duplication of 2q14 and deletion of 2q37 in a patient with autism

We describe a patient with autism and a paracentric inversion of chromosome 2q14.2q37.3, with a concurrent duplication of the proximal breakpoint at 2q14.1q14.2 and a deletion of the distal breakpoint at 2q37.3. The abnormality was derived from his mother with a balanced paracentric inversion. The inversion in the child appeared to be cytogenetically balanced but subtelomere FISH revealed a cryptic deletion at the 2q37.3 breakpoint. High-resolution single nucleotide polymorphism array confirmed the presence of a 3.5 Mb deletion that extended to the telomere, and showed a 4.2 Mb duplication at 2q14.1q14.2. FISH studies using a 2q14.2 probe showed that the duplicated segment was located at the telomeric end of chromosome 2q. This recombinant probably resulted from breakage of a dicentric chromosome. The child had autism, mental retardation, speech and language delay, hyperactivity, growth retardation with growth hormone deficiency, insulin-dependent diabetes, and mild facial dysmorphism. Most of these features have been previously described in individuals with simple terminal deletion of 2q37. Pure duplications of the proximal chromosome 2q are rare and no specific syndrome has been defined yet, so the contribution of the 2q14.1q14.2 duplication to the phenotype of the patient is unknown. These findings underscore the need to explore apparently balanced chromosomal rearrangements inherited from a phenotypically normal parent in subjects with autism and/or developmental delay. In addition, they provide further evidence indicating that chromosome 2q terminal deletions are among the most frequently reported cytogenetic abnormalities in individuals with autism.

Molecular characterization of a de novo 6q24.2q25.3 duplication interrupting UTRN in a patient with arthrogryposis

Chromosome 6q duplications have been documented repeatedly, allowing the delineation of a "6q duplication syndrome," characterized by hypertelorism, downslanting palpebral fissures, tented upper lip, short neck, severe mental and growth retardation, and joint contractures. Most reported cases result from malsegregation of a reciprocal translocation leading to a terminal 6q duplication and partial monosomy of another chromosome. Only 11 cases of de novo pure duplication have been reported so far. The breakpoints do not appear to be recurrent, but in most cases they have not been characterized molecularly, precluding genotype-phenotype correlation. We report on an 8-year-old girl with a phenotype consistent with mild 6q duplication syndrome, including characteristic physical findings, mild mental retardation, and joint contractures. She carries a 13 Mb de novo 6q24.2q25.3 duplication, diagnosed by high-resolution karyotype and confirmed by array-CGH. Molecular characterization of the duplicated segment with quantitative PCR showed that the proximal breakpoint is localized within the UTRN gene, encoding utrophin, the autosomal homologue of dystrophin. We discuss the possible implication of UTRN in arthrogryposis associated with duplications spanning the 6q23q26 region.

Ectodermal dysplasia-like syndrome with mental retardation due to contiguous gene deletion: further clinical and molecular delineation of del(2q32) syndrome

We report on a patient with an interstitial deletion of the long arm of chromosome 2 at 2q31.2q33.2. She had prenatal and postnatal growth retardation, microcephaly, facial dysmorphism, cleft palate, camptodactyly, bilateral talipes equinovarus, severe intellectual disability, and ectodermal anomalies. She showed thin, atrophic skin, sparse, brittle, slowly growing hair, oligodontia with abnormally shaped teeth, normal sweating, and normal fingernails, consistent with a diagnosis of ectodermal dysplasia. Array CGH analysis (Agilent 44K) showed the deletion to span 26 Mb, between cytogenetic bands 2q31.2 and 2q33. The deletion leads to hemizygosity for the HOXD cluster and its regulatory elements, COL3A1/COL5A2, GTF3C3, CASP8, CASP10, and SABT2 could perhaps interfere with long range control of DLX1 and DLX2 expression. This girl confirms the existence of a clinically recognizable 2q32 microdeletion syndrome, as recently delineated by Van Buggenhout et al. and confirms a novel putative locus for ectodermal dysplasia on chromosome 2q31q33. We recommend considering cytogenetic and/or molecular screening for del(2q32) in patients with developmental disability and ectodermal dysplasia-like phenotype, including thin skin, oligodontia, dysplastic teeth, and sparse hair.

Chromosome 22q13.3 deletion syndrome with a de novo interstitial 22q13.3 cryptic deletion disrupting SHANK3

BACKGROUND

The 22q13.3 deletion syndrome (or Phelan-McDermid syndrome, MIM 606232) is characterized by developmental delay, absent or severely delayed speech, neonatal hypotonia, autistic behavior, normal to accelerated growth, and minor dysmorphic facial features. Among the three genes in the minimal critical region (from the centromere to the telomere: SHANK3, ACR and RABL2B), the defect in the SHANK3 gene is considered to be the cause of the neurobehavioral symptoms.

OBJECTIVE

We describe the molecular characterization of a de novo interstitial del(22)(q13.3q13.3) disrupting the SHANK3 gene in a child with a phenotype compatible with the 22q13.3 deletion syndrome.

METHODS

Clinical work-up included clinical histories, physical, neurological, and ophthalmological examinations, and imaging of the brain. Commercially available MLPA for subtelomeric analysis, FISH specific probes and quantitative real-time PCR were used to characterize the rearrangement.

RESULTS

Subtelomere analysis by MLPA showed a discrepancy between P036B and P070 kits (MCR Holland): the P070 MLPA 22q probe (targeting the ARSA gene) showed a deletion but the P036B one (targeting the RABL2B gene) showed a normal result. FISH analysis using LSI TUPLE1/LSI ARSA (Vysis) probes confirmed deletion of ARSA, whereas FISH with N25/N85A3 (Cytocell) probes, targeting the SHANK3 locus was normal. Supplemented FISH analysis using BAC clones allowed us to specify the centromeric breakpoint region of the interstitial deletion between clones RP11-354I12 and RP11-232E17, at less than 2 Mb from the telomere. Quantitative real-time PCR of exon 5, 22 and 24 and intron 9 of SHANK3 showed that the telomeric breakpoint occurred between intron 9 and exon 22.

CONCLUSIONS

These data highlight the difficulty of performing an appropriate test aimed at looking for cryptic 22q13.3 deletion. Furthermore, the molecular characterization of this interstitial 22q13.3 deletion contributes to the clinical and genetic delineation of the 22q13.3 deletion syndrome.

Semilobar holoprosencephaly prenatal diagnosis: an unexpected complex rearrangement in ade novo apparently balanced reciprocal translocation on karyotype

We report a semilobar holoprosencephaly (HPE) in a post-intracytoplasmic-sperm-injection pregnancy. It was suggested by ultrasonography (US), documented on karyotype, identified with magnetic resonance imaging (MRI), established after birth and confirmed on post-mortem autopsy. An amniocentesis revealed a de novo apparently balanced reciprocal translocation 46,XY, t(7;8) (q31.3;q12). Fluorescence in situ hybridization (FISH) identified a deletion in the region of the Sonic Hedgehog gene (SHH) on der(8); nevertheless, the subtelomeric regions for chromosomes 7 and 8 were present. The parents decided to continue the pregnancy; a boy was born and survived for 3 days. The brain autopsy confirmed the semilobar HPE previously noted on US and MRI. Further, band-specific FISH revealed, in addition to SHH deletion, the presence of an inversion in the 7q translocated material on der(8). The parents' karyotypes were normal. An unexpected complex rearrangement was present in a de novo apparently balanced reciprocal translocation in a semilobar HPE.

Prenatal diagnosis and characterization of an analphoid marker chromosome 16

We report on a fetus with intrauterine growth retardation and multiple malformations diagnosed on ultrasound at 32 weeks. Examination of amniotic fluid cells in culture showed a 47,XY, i(16)(q10), +mar karyotype. Chromosome analysis of both parents was normal. Using spectral karyotyping, we identified the marker chromosome as a mitotically stable acentric marker chromosome derived from chromosome 16. Further studies using subtelomeric fluorescent probes confirmed the presence of an isochromosome for the long arm of chromosome 16 and showed that the acentric marker chromosome derived from the short arm of chromosome 16 leading to a trisomy for the long arm of chromosome 16. After genetic counseling, the parents decided to terminate the pregnancy. Fetal autopsy showed a male fetus with ambiguous external genitalia, cardiac malformation, megacystis and limbs anomalies as observed in other cases of trisomy for the long arm of chromosome 16. In addition, fetal brain examination showed vermian and olfactory bulb hypoplasia.