A French multicenter study of over 700 patients with 22q11 deletions diagnosed using FISH or aCGH.

Although 22q11.2 deletion syndrome (22q11.2DS) is the most recurrent human microdeletion syndrome associated with a highly variable phenotype, little is known about the condition's true incidence and the phenotype at diagnosis. We performed a multicenter, retrospective analysis of postnatally diagnosed patients recruited by members of the Association des Cytogénéticiens de Langue Française (the French-Speaking Cytogeneticists Association). Clinical and cytogenetic data on 749 cases diagnosed between 1995 and 2013 were collected by 31 French cytogenetics laboratories. The most frequent reasons for referral of postnatally diagnosed cases were a congenital heart defect (CHD, 48.6%), facial dysmorphism (49.7%) and developmental delay (40.7%). Since 2007 (the year in which array comparative genomic hybridization (aCGH) was introduced for the routine screening of patients with intellectual disability), almost all cases have been diagnosed using FISH (96.1%). Only 15 cases (all with an atypical phenotype) were diagnosed with aCGH; the deletion size ranged from 745 to 2904 kb. The deletion was inherited in 15.0% of cases and was of maternal origin in 85.5% of the latter. This is the largest yet documented cohort of patients with 22q11.2DS (the most commonly diagnosed microdeletion) from the same population. French cytogenetics laboratories diagnosed at least 108 affected patients (including fetuses) per year from among a national population of ∼66 million. As observed for prenatal diagnoses, CHDs were the most frequently detected malformation in postnatal diagnoses. The most common CHD in postnatal diagnoses was an isolated septal defect.

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.

Phenotype-genotype correlations in 17 new patients with an Xp11.23p11.22 microduplication and review of the literature.

Array comparative genomic hybridization (array CGH) has proven its utility in uncovering cryptic rearrangements in patients with X-linked intellectual disability. In 2009, Giorda et al. identified inherited and de novo recurrent Xp11.23p11.22 microduplications in two males and six females from a wide cohort of patients presenting with syndromic intellectual disability. To date, 14 females and 5 males with an overlapping microduplication have been reported in the literature. To further characterize this emerging syndrome, we collected clinical and microarray data from 17 new patients, 10 females, and 7 males. The Xp11.23p11.2 microduplications detected by array CGH ranged in size from 331 Kb to 8.9 Mb. Five patients harbored 4.5 Mb recurrent duplications mediated by non-allelic homologous recombination between segmental duplications and 12 harbored atypical duplications. The chromosomal rearrangement occurred de novo in eight patients and was inherited in six affected males from three families. Patients shared several common major characteristics including moderate to severe intellectual disability, early onset of puberty, language impairment, and age related epileptic syndromes such as West syndrome and focal epilepsy with activation during sleep evolving in some patients to continuous spikes-and-waves during slow sleep. Atypical microduplications allowed us to identify minimal critical regions that might be responsible for specific clinical findings of the syndrome and to suggest possible candidate genes: FTSJ1 and SHROOM4 for intellectual disability along with PQBP1 and SLC35A2 for epilepsy. Xp11.23p11.22 microduplication is a recently-recognized syndrome associated with intellectual disability, epilepsy, and early onset of puberty in females. In this study, we propose several genes that could contribute to the phenotype.

17q21.31 microdeletion: brain anomalies leading to prenatal diagnosis.

Ultrasound examination performed on a 36-year-old woman at 33 weeks of gestation showed the presence of isolated and bilateral ventriculomegaly in the fetus. Array-based comparative genomic hybridization (array-CGH) performed on uncultured amniocytes at 35 weeks of gestation revealed a 17q21.31 microdeletion. After genetic counseling, the pregnancy was terminated at 37 weeks of gestation. At autopsy, the fetus displayed facial dysmorphic features and triventricular ventriculomegaly. To our knowledge, this is the first case of a 17q21.31 microdeletion detected prenatally. Our report suggests that array-CGH should be performed when severe ventriculomegaly is observed in prenatal ultrasound examination.

Identification of the IRXB gene cluster as candidate genes in severe dysgenesis of the ocular anterior segment.

PURPOSE: Anterior segment ocular dysgenesis (ASOD) is a broad heterogeneous group of diseases detectable at the clinical and molecular level. In a patient with bilateral congenital ASOD including aniridia and aphakia, a complex chromosomal rearrangement, inv(2)(p22.3q12.1)t(2;16)(q12.1;q12.2), was characterized at the molecular level, to identify candidate genes implicated in ASOD. METHODS: After negative sequencing of the PAX6, FOXC1, and PITX2 genes, we used fluorescence in situ hybridization (FISH) and Southern blot analysis to characterize the chromosomal breakpoints. Candidate genes were selected, and in situ tissue expression analysis was performed on human fetuses and embryos. RESULTS: Molecular analyses showed that the 16q12.2 breakpoint in this rearrangement occurs in a 625-bp region centromeric to the IRX3 gene, which belongs to the IRXB cluster. In situ hybridization expression studies showed that during early human embryonic development, the IRX3 gene is expressed in the anterior segment of the eye. Of interest, it has been shown previously that a highly conserved noncoding region (HCNCR) is located 300 kb centromeric to the IRX3 gene and induces, in a murine transgenic assay, an expression pattern fitting that of the IRX3 gene. CONCLUSIONS: The authors propose that the 16q12.2 breakpoint of this complex translocation is causally related to the ocular anterior segment dysgenesis observed in this patient. This translocation is assumed to separate the HCNCR from the IRXB cluster genes, thus deregulating the IRXB cluster and leading to the ASOD observed by a positional effect.

Neurobehavioral profile and brain imaging study of the 22q13.3 deletion syndrome in childhood.

OBJECTIVE: The 22q13.3 deletion syndrome (Online Mendelian Inheritance in Man No. 606232) is a neurodevelopmental disorder that includes hypotonia, severely impaired development of speech and language, autistic-like behavior, and minor dysmorphic features. Although the number of reported cases is increasing, the 22q13.3 deletion remains underdiagnosed because of failure in recognizing the clinical phenotype and detecting the 22qter deletion by routine chromosome analyses. Our goal is to contribute to the description of the neurobehavioral phenotype and brain abnormalities of this microdeletional syndrome. METHODS: We assessed neuromotor, sensory, language, communication, and social development and performed cerebral MRI and study of regional cerebral blood flow measured by positron emission tomography in 8 children carrying the 22q13.3 deletion. RESULTS: Despite variability in expression and severity, the children shared a common developmental profile characterized by hypotonia, sleep disorders, and poor response to their environment in early infancy; expressive language deficit contrasting with emergence of social reciprocity from ages approximately 3 to 5 years; sensory processing dysfunction; and neuromotor disorders. Brain MRI findings were normal or showed a thin or morphologically atypical corpus callosum. Positron emission tomography study detected a localized dysfunction of the left temporal polar lobe and amygdala hypoperfusion. CONCLUSIONS: The developmental course of the 22q13.3 deletion syndrome belongs to pervasive developmental disorders but is distinct from autism. An improved description of the natural history of this syndrome should help in recognizing this largely underdiagnosed condition.

Microphthalmia with linear skin defects (MLS) syndrome: clinical, cytogenetic, and molecular characterization of 11 cases.

The microphthalmia with linear skin defects (MLS) syndrome (MIM 309801) is a severe and rare developmental disorder, which is inherited as an X-linked dominant trait with male lethality. In the vast majority of patients, this syndrome is associated with terminal deletion of the Xp22.3 region. Thirty-five cases have been described to date in the literature since the first description of the syndrome in the early 1990s. We now report on the clinical, cytogenetic, and molecular characterization of 11 patients, 7 of whom have not been described previously. Seven of these patients have chromosomal abnormalities of the short arm of the X-chromosome, which were characterized and defined by fluorescence in situ hybridization (FISH) analysis. Intriguingly, one of the patients displays an interstitial Xp22.3 deletion, which to the best of our knowledge is the first reported for this condition. Finally we report on the identification and molecular characterization of four cases with clinical features of MLS but apparently normal karyotypes, verified by FISH analysis using genomic clones spanning the MLS minimal critical region, and with genome-wide analysis using a 1 Mb resolution BAC microarray. These patients made it possible to undertake mutation screening of candidate genes and may prove critical for the identification of the gene responsible for this challenging and intriguing genetic disease.

Functional disomy of the Xq28 chromosome region.

We report on two patients, a boy and a girl, with an additional Xq28 chromosome segment translocated onto the long arm of an autosome. The karyotypes were 46,XY,der(10)t(X;10)(q28;qter) and 46,XX,der(4)t(X;4)(q28;q34), respectively. In both cases, the de novo cryptic unbalanced X-autosome translocation resulted in a Xq28 chromosome functional disomy. To our knowledge, at least 17 patients with a distal Xq chromosome functional disomy have been described in the literature. This is the third report of a girl with an unbalanced translocation yielding such a disomy. When the clinical features of both patients are compared to those observed in patients reported in the literature, a distinct phenotype emerges including severe mental retardation, facial dysmorphic features with a wide face, a small mouth and a thin pointed nose, major axial hypotonia, severe feeding problems and proneness to infections. A clinically oriented FISH study using subtelomeric probes is necessary to detect such a cryptic rearrangement.

Failure to detect an 8p22-8p23.1 duplication in patients with Kabuki (Niikawa-Kuroki) syndrome.

Kabuki syndrome (KS) is a rare MCA/MR syndrome with an estimated frequency of 1/32 000 in Japan. This syndrome is characterized by postnatal growth retardation, distinctive facial features, dermatoglyphic anomalies, skeletal dysplasia, and mental retardation. The molecular basis of KS remains unknown. Recently, Milunsky and Huang reported on six unrelated patients with a clinical diagnosis of KS and an 8p22-8p23.1 duplication using comparative genomic hybridization and BAC-FISH studies. Also, they suggested that a paracentric inversion may contribute to the occurrence of KS. In the present study, 24 patients with a clinical diagnosis of KS based on Niikawa-Kuroki criteria have been collected. They were tested for the presence of an 8p duplication using the same clones as described by Milunsky and Huang. Our results do not confirm the previously described association between KS and an 8p22-8p23.1 duplication.

Werner mesomelic dysplasia with Hirschsprung disease.

Mesomelic dysplasia type Werner is defined by absence of tibiae and preaxial polysyndactyly of hands and feet. Occasional findings are triphalangeal thumbs, absence of patella(e), and dislocated fibula(e). The molecular basis is unknown and autosomal dominant inheritance with variable expressivity is currently postulated. Hirschsprung disease was reported previously in one case. We report here on a new case of mesomelic dysplasia Werner type associated with Hirschsprung disease and bilateral cryptorchidism. We discuss the overlap with the triphalangeal thumb polysyndactyly syndrome located in chromosome 7q36.

Overgrowth and trisomy 15q26.1-qter including the IGF1 receptor gene: report of two families and review of the literature.

Overgrowth is rarely associated with chromosomal imbalances. Here we report on four children from two unrelated families presenting with overgrowth and a terminal duplication of the long arm of chromosome 15 diagnosed using cytogenetic and FISH studies. In both cases, chromosome analysis of the parents showed a balanced translocation involving 15q26.1-qter. Molecular and cytogenetic studies showed three copies of the insulin-like growth factor 1 receptor (IGF1R) gene. This finding suggests that overgrowth observed in our patients might be causally related to a dosage effect of the IGF1R gene, in contrast to severe growth retardation observed in patients with terminal deletion of 15q. The present observation emphasises the importance of chromosome analysis in patients with overgrowth and mental retardation. Moreover, it further delineates a specific phenotype related to trisomy 15q26.1-qter with macrosomia at birth, overgrowth, macrocephaly and mild developmental delay being the major clinical features.