De novo interstitial deletion 2q14.1q22.1: is there a recognizable phenotype?

In this report we describe a male patient with a rare de novo interstitial deletion of chromosome 2q14.1-q22.1. His karyotype was reported as 46,XY,del(2)(q13q21) but subsequent array comparative genomic hybridization (array CGH) analysis redefined the deletion breakpoints as 2q14.1 and 2q22.1. Eight patients have been reported with deletions either within or spanning the region 2q13 or 2q14 to 2q22.1. In five patients the diagnosis was made by karyotype analysis alone and in three reported patients and the proband array CGH analysis was also performed. When the proband was compared with the eight previously reported patients it was apparent that they shared many clinical findings suggesting that patients with a de novo interstitial deletion involving 2q13 or 2q14 to 2q21 or 2q22 may have a recognizable phenotype. There are 14 known disease-associated genes in the deleted region of 2q14.1-q22.1 and their possible phenotypic effects on the proband and the eight previously reported patients are discussed.

Perspective on the technical challenges involved in the implementation of array-CGH in prenatal diagnostic testing.

Our aim was to construct a streamlined technical workflow to facilitate a prospective, multi-centre evaluation of array comparative genomic hybridisation (array-CGH) in the prenatal diagnostic context. A collection of commercially available DNA extraction and quantification techniques were evaluated and compared using minimal quantities of amniotic fluid, chorionic villi and cultured cells. When prenatal DNA of suitable quality and quantity was obtained, array-CGH was performed using Oxford Gene Technology's (OGT, Oxford, UK) CytoSure™ ISCA 8 × 60 K oligo array platform. With starting quantities of 2-4 ml amniotic fluid, 2-5 mg chorionic villi or under 150,000 cultured cells the following optimised technical workflow was identified: DNA extraction using the iGENatal™ kit (igenbiotech, Madrid, Spain) and quantification by the Qubit® 2.0 Fluorometer with the Qubit® dsDNA BR assay kit (Invitrogen™, Eugene, OR, USA). In addition, it was elucidated that array-CGH can be successfully performed with as little as 125 ng DNA in the experiment using the OGT CytoSure™ ISCA 8 × 60 K oligo array platform. Amidst an on-going debate on whether array-CGH should be applied in the prenatal diagnostic setting, by following the technical recommendations described here genetics laboratories can now gain exposure to prenatal array-CGH testing without compromising the conventional karyotype result.

The clinical utility of microarray technologies applied to prenatal cytogenetics in the presence of a normal conventional karyotype: a review of the literature.

The clinical utility of microarray technologies when used in the context of prenatal diagnosis lies in the technology's ability to detect submicroscopic copy number changes that are associated with clinically significant outcomes. We have carried out a systematic review of the literature to calculate the utility of prenatal microarrays in the presence of a normal conventional karyotype. Amongst 12,362 cases in studies that recruited cases from all prenatal ascertainment groups, 295/12,362 (2.4%) overall were reported to have copy number changes with associated clinical significance (pCNC), 201/3090 (6.5%) when ascertained with an abnormal ultrasound, 50/5108 (1.0%) when ascertained because of increased maternal age and 44/4164 (1.1%) for all other ascertainment groups (e.g. parental anxiety and abnormal serum screening result). When additional prenatal microarray studies are included in which ascertainment was restricted to fetuses with abnormal ultrasound scans, 262/3730 (7.0%) were reported to have pCNCs.

Duplication of 17q11.2 and Features of Albright Hereditary Osteodystrophy Secondary to Methylation Defects within the GNAS Cluster: Coincidence or Causal?

We report a case of Albright hereditary osteodystrophy (AHO) in a three-year-old girl with a microduplication at 17q11.2. The child developed obesity within the first 6 months of life. A diagnosis of Albright was made at age 2 years when biochemical evidence of parathyroid resistance was found. No mutations were identified in guanine nucleotide-binding protein G (s) subunit alpha (GNAS1). Subsequent investigations revealed methylation disturbance at GNAS1A, neuroendocrine secretory protein antisense (NESPAS) and neuroendocrine secretory protein 55 (NESP55) confirming a diagnosis of pseudohypothyroidism type 1B. A deletion of NESP55 and uniparental disomy chromosome 20 were excluded which suggested that the features of AHO arose through a purely epigenetic mechanism. Further investigation revealed a de novo microduplication at 17q11.2 encompassing the neurofibromatosis type 1 (NF1) gene. The combination of two rare de novo events in the same child raises the possibility that duplication of a gene within the 17q11.2 region may have triggered abnormal methylation in the GNAS cluster region on chromosome 20.

8p23.1 duplication syndrome; common, confirmed, and novel features in six further patients.

The 8p23.1 duplication syndrome is a relatively rare genomic condition that has been confirmed with molecular cytogenetic methods in only 11 probands and five family members. Here, we describe another prenatal and five postnatal patients with de novo 8p23.1 duplications analyzed with oligonucleotide array comparative genomic hybridization (oaCGH). Of the common features, mild or moderate developmental delays and/or learning difficulties have been found in 11/12 postnatal probands, a variable degree of mild dysmorphism in 8/12 and congenital heart disease (CHD) in 4/5 prenatal and 3/12 postnatal probands. Behavioral problems, cleft lip and/or palate, macrocephaly, and seizures were confirmed as additional features among the new patients, and novel features included neonatal respiratory distress, attention deficit hyperactivity disorder (ADHD), ocular anomalies, balance problems, hypotonia, and hydrocele. The core duplication of 3.68 Mb contains 31 genes and microRNAs of which only GATA4, TNKS, SOX7, and XKR6 are likely to be dosage sensitive genes and MIR124-1 and MIR598 have been implicated in neurocognitive phenotypes. A combination of the duplication of GATA4, SOX7, and related genes may account for the variable penetrance of CHD. Two of the duplications were maternal and intrachromosomal in origin with maternal heterozygosity for the common inversion between the repeats in 8p23.1. These additional patients and the absence of the 8p23.1 duplications in published controls, indicate that the 8p23.1 duplication syndrome may now be considered a pathogenic copy number variation (pCNV) with an estimated population prevalence of 1 in 58,000.

Evaluation of a novel assay for detection of the fetal marker RASSF1A: facilitating improved diagnostic reliability of noninvasive prenatal diagnosis.

BACKGROUND: Analysis of cell free fetal (cff) DNA in maternal plasma is used routinely for non invasive prenatal diagnosis (NIPD) of fetal sex determination, fetal rhesus D status and some single gene disorders. True positive results rely on detection of the fetal target being analysed. No amplification of the target may be interpreted either as a true negative result or a false negative result due to the absence or very low levels of cffDNA. The hypermethylated RASSF1A promoter has been reported as a universal fetal marker to confirm the presence of cffDNA. Using methylation-sensitive restriction enzymes hypomethylated maternal sequences are digested leaving hypermethylated fetal sequences detectable. Complete digestion of maternal sequences is required to eliminate false positive results. METHODS: cfDNA was extracted from maternal plasma (n = 90) and digested with methylation-sensitive and insensitive restriction enzymes. Analysis of RASSF1A, SRY and DYS14 was performed by real-time PCR. RESULTS: Hypermethylated RASSF1A was amplified for 79 samples (88%) indicating the presence of cffDNA. SRY real time PCR results and fetal sex at delivery were 100% accurate. Eleven samples (12%) had no detectable hypermethylated RASSF1A and 10 of these (91%) had gestational ages less than 7 weeks 2 days. Six of these samples were male at delivery, five had inconclusive results for SRY analysis and one sample had no amplifiable SRY. CONCLUSION: Use of this assay for the detection of hypermethylated RASSF1A as a universal fetal marker has the potential to improve the diagnostic reliability of NIPD for fetal sex determination and single gene disorders.

The use of mouth brushings for screening girls who present with inguinal hernia for complete androgen insensitivity syndrome.

INTRODUCTION: Published guidance recommends that all girls with inguinal hernia should be screened for complete androgen insensitivity syndrome (CAIS). We report a novel, noninvasive screening technique. METHODS: Retrospective review of all girls undergoing inguinal herniotomy from April 2009 to October 2010. Those screened using the novel technique of extraction of Y chromosome specific DNA from a buccal mucosal sample obtained by mouth brushing are reported. RESULTS: A total of 29 girls were screened by mouth brushing at median age 2.9 years (range 29 days to 9.3 years). Of the 29 samples, 25 were adequate for DNA extraction; 4 were inadequate and screening was repeated (3 repeat mouth brushing, 1 perioperative blood test). Mouth brushing was well tolerated by children and acceptable to parents. A preoperative blood test was avoided in all girls who had a mouth brushing. None of the girls in this study had CAIS. Turn-around time for mouth brushing was mean 4.9 days compared with a minimum of 10 days for a karyotype. This technique is cheaper than a karyotype (£ 87 vs. £ 205). CONCLUSION: Extraction of Y chromosome specific DNA from a mouth brushing sample is effective for screening girls with inguinal hernia for CAIS. It is acceptable, cheaper, and quicker than alternatives.

Parental insertional balanced translocations are an important cause of apparently de novo CNVs in patients with developmental anomalies.

In several laboratories, genome-wide array analysis has been implemented as the first tier diagnostic test for the identification of copy number changes in patients with mental retardation and/or congenital anomalies. The identification of a pathogenic copy number variant (CNV) is not only important to make a proper diagnosis but also to enable the accurate estimation of the recurrence risk to family members. Upon the identification of a de novo interstitial loss or gain, the risk recurrence is considered very low. However, this risk is 50% if one of the parents is carrier of a balanced insertional translocation (IT). The apparently de novo imbalance in a patient is then the consequence of the unbalanced transmission of a derivative chromosome involved in an IT. To determine the frequency with which insertional balanced translocations would be the origin of submicroscopic imbalances, we investigated the potential presence of an IT in a consecutive series of 477 interstitial CNVs, in which the parental origin has been tested by FISH, among 14,293 patients with developmental abnormalities referred for array. We demonstrate that ITs underlie ~2.1% of the apparently de novo, interstitial CNVs, indicating that submicroscopic ITs are at least sixfold more frequent than cytogenetically visible ITs. This risk estimate should be taken into account during counseling, and warrant parental and proband FISH testing wherever possible in patients with an apparently de novo, interstitial aberration.

De novo deletions and duplications detected by array CGH: a study of parental origin in relation to mechanisms of formation and size of imbalance.

We report a large series of 173 patients with physical and/or neurological abnormalities and a de novo imbalance identified by array CGH. Breakpoint intervals were screened for the presence of low copy repeats (LCRs) to distinguish between rearrangements formed by non-allelic homologous recombination (NAHR) and rearrangements formed by other mechanisms. We identified significant differences in size and parental origin between the LCR-mediated and non-LCR groups. Non-LCR imbalances were evenly distributed among the four size intervals we defined, whereas LCR-mediated rearrangements had a narrow size distribution, predominantly between 1 and 5 Mb (P = 0.001). Among the LCR-mediated rearrangements there were equal numbers of maternally and paternally derived cases. In contrast, for the non-LCR rearrangements there was a significant excess of paternal cases (P = 0.024) over a wide size range including below 1 Mb. Our results provide novel evidence that unbalanced chromosome rearrangements are not only more frequent in males, but may also arise through different mechanisms than those seen in females. Although the paternal imbalances identified in our study are evenly distributed throughout the four size groups, there are very few maternal imbalances either <1 Mb or >10 Mb. Furthermore, a lower proportion of paternal imbalances are LCR mediated (13/71) compared with the maternal imbalances (12/30). We hypothesise that imbalances of maternal origin arise predominantly through NAHR during meiosis, while the majority of imbalances of paternal origin arise through male-specific mechanisms other than NAHR. Our data suggest that mitotic mechanisms could be important for the formation of chromosome imbalances; however, we found no association with increased paternal age.

An evidence-based approach to establish the functional and clinical significance of copy number variants in intellectual and developmental disabilities.

PURPOSE: Copy number variants have emerged as a major cause of human disease such as autism and intellectual disabilities. Because copy number variants are common in normal individuals, determining the functional and clinical significance of rare copy number variants in patients remains challenging. The adoption of whole-genome chromosomal microarray analysis as a first-tier diagnostic test for individuals with unexplained developmental disabilities provides a unique opportunity to obtain large copy number variant datasets generated through routine patient care. METHODS: A consortium of diagnostic laboratories was established (the International Standards for Cytogenomic Arrays consortium) to share copy number variant and phenotypic data in a central, public database. We present the largest copy number variant case-control study to date comprising 15,749 International Standards for Cytogenomic Arrays cases and 10,118 published controls, focusing our initial analysis on recurrent deletions and duplications involving 14 copy number variant regions. RESULTS: Compared with controls, 14 deletions and seven duplications were significantly overrepresented in cases, providing a clinical diagnosis as pathogenic. CONCLUSION: Given the rapid expansion of clinical chromosomal microarray analysis testing, very large datasets will be available to determine the functional significance of increasingly rare copy number variants. This data will provide an evidence-based guide to clinicians across many disciplines involved in the diagnosis, management, and care of these patients and their families.

Phenotypic variability of distal 22q11.2 copy number abnormalities.

The availability of microarray technology has led to the recent recognition of copy number abnormalities of distal chromosome 22q11.2 that are distinct from the better-characterized deletions and duplications of the proximal region. This report describes five unrelated individuals with copy number abnormalities affecting distal chromosome 22q11.2. We report on novel phenotypic features including diaphragmatic hernia and uterine didelphys associated with the distal microdeletion syndrome; and frontomedial polymicrogyria and callosal agenesis associated with the distal microduplication syndrome. We describe the third distal chromosome 22q11.2 microdeletion patient with Goldenhar syndrome. Patients with distal chromosome 22q11.2 copy number abnormalities exhibit inter- and intra-familial phenotypic variability, and challenge our ability to draw meaningful genotype-phenotype correlations.

The 12q14 microdeletion syndrome: six new cases confirming the role of HMGA2 in growth.

We report six patients with array deletions encompassing 12q14. Out of a total of 2538 array investigations carried out on children with developmental delay and dysmorphism in three diagnostic testing centres, six positive cases yielded a frequency of 1 in 423 for this deletion syndrome. The deleted region in each of the six cases overlaps significantly with previously reported cases with microdeletions of this region. The chromosomal range of the deletions extends from 12q13.3q15. In the current study, we report overlapping deletions of variable extent and size but primarily comprising chromosomal bands 12q13.3q14.1. Four of the six deletions were confirmed as de novo events. Two cases had deletions that included HMGA2, and both children had significant short stature. Neither case had osteopoikilosis despite both being deleted for LEMD3. Four cases had deletions that ended proximal to HMGA2 and all of these had much better growth. Five cases had congenital heart defects, including two with atrial septal defects, one each with pulmonary stenosis, sub-aortic stenosis and a patent ductus. Four cases had moderate delay, two had severe developmental delay and a further two had a diagnosis of autism. All six cases had significant speech delay with subtle facial dysmorphism.

Large de novo deletion of 7p15.1 to 7p12.1 involving the imprinted gene GRB10 associated with a complex phenotype including features of Beckwith Wiedemann syndrome.

We present an infant with a de novo cytogenetically visible interstitial deletion of approximately 21.9Mb involving chromosome bands 7p15.1-7p12.1, with the loss of 119 genes confirmed by array CGH. The infant had a ventricular septal defect, hand and skull anomalies, and hyperglycaemia compatible with haploinsufficiency of TBX20, GLI3, and GCK genes, respectively. In addition, the infant had some features reminiscent of Beckwith Wiedemann syndrome including macroglossia, umbilical hernia, and a relatively large birth weight and we speculate that this is due to the deletion of GRB10, an imprinted gene on chromosome 7. This report illustrates how knowledge of genes within a deleted interval facilitates optimal medical management, can explain observed phenotypes, and stimulates research questions.

Symmetrical enchondromatosis is associated with duplication of 12p11.23 to 12p11.22 including PTHLH.

We describe a patient with striking generalized symmetrical enchondromatosis of the tubular bones and a de novo duplication of chromosome 12p11.23 to 12p11.22. The PTHLH gene within this region encodes a ligand for PTHR1: mutations in the gene encoding this receptor are associated with some cases of Ollier disease, several skeletal dysplasias including Blomstrand, Eiken, and Jansen and down-regulation of PTHLH expression in brachydactyly type E. Our findings suggest that abnormal PTHLH-PTHR1 signaling may underly this unusual form of enchondromatosis and indicate that unlike most cases of Ollier disease it is dominantly inherited.

Deletion 17q12 is a recurrent copy number variant that confers high risk of autism and schizophrenia.

Autism spectrum disorders (ASD) and schizophrenia are neurodevelopmental disorders for which recent evidence indicates an important etiologic role for rare copy number variants (CNVs) and suggests common genetic mechanisms. We performed cytogenomic array analysis in a discovery sample of patients with neurodevelopmental disorders referred for clinical testing. We detected a recurrent 1.4 Mb deletion at 17q12, which harbors HNF1B, the gene responsible for renal cysts and diabetes syndrome (RCAD), in 18/15,749 patients, including several with ASD, but 0/4,519 controls. We identified additional shared phenotypic features among nine patients available for clinical assessment, including macrocephaly, characteristic facial features, renal anomalies, and neurocognitive impairments. In a large follow-up sample, the same deletion was identified in 2/1,182 ASD/neurocognitive impairment and in 4/6,340 schizophrenia patients, but in 0/47,929 controls (corrected p = 7.37 × 10⁻5). These data demonstrate that deletion 17q12 is a recurrent, pathogenic CNV that confers a very high risk for ASD and schizophrenia and show that one or more of the 15 genes in the deleted interval is dosage sensitive and essential for normal brain development and function. In addition, the phenotypic features of patients with this CNV are consistent with a contiguous gene syndrome that extends beyond RCAD, which is caused by HNF1B mutations only.

Refinement of causative genes in monosomy 1p36 through clinical and molecular cytogenetic characterization of small interstitial deletions.

Monosomy 1p36 is the most common terminal deletion syndrome seen in humans, occurring in approximately 1 in 5,000 live births. Common features include mental retardation, characteristic dysmorphic features, hypotonia, seizures, hearing loss, heart defects, cardiomyopathy, and behavior abnormalities. Similar phenotypes are seen among patients with a variety of deletion sizes, including terminal and interstitial deletions, complex rearrangements, and unbalanced translocations. Consequently, critical regions harboring causative genes for each of these features have been difficult to identify. Here we report on five individuals with 200-823 kb overlapping deletions of proximal 1p36.33, four of which are apparently de novo. They present with features of monosomy 1p36, including developmental delay and mental retardation, dysmorphic features, hypotonia, behavioral abnormalities including hyperphagia, and seizures. The smallest region of deletion overlap is 174 kb and contains five genes; these genes are likely candidates for some of the phenotypic features in monosomy 1p36. Other genes deleted in a subset of the patients likely play a contributory role in the phenotypes, including GABRD and seizures, PRKCZ and neurologic features, and SKI and dysmorphic and neurologic features. Characterization of small deletions is important for narrowing critical intervals and for the identification of causative or candidate genes for features of monosomy 1p36 syndrome.