Small terminal deletions of the long arm of chromosome 2: two new cases

Genotype and phenotype correlation in 103 individuals with 2q37 deletion syndrome reveals incomplete penetrance and supports HDAC4 as the primary genetic contributor

The 2q37 deletion syndrome, also described in the literature as brachydactyly-mental retardation syndrome (MIM 600430), is caused by deletion or haploinsufficiency of the HDAC4 gene, which encodes the histone deacetylase 4 protein. Although the most commonly described hallmark features of the 2q37 deletion syndrome include brachydactyly type E, developmental delay, obesity, autistic features, and craniofacial or skeletal dysmorphism, a literature review of 101 published cases plus two newly reported individuals indicates that there is a high degree of variability in the presence of some of the features that are considered the most characteristic of the syndrome: overweight and obesity (34%), cognitive-behavioral issues (79%), dysmorphic craniofacial features (86%), and type E brachydactyly (48%). These features overlap with other neurodevelopmental conditions, including Smith-Magenis syndrome (SMS), and may be incompletely penetrant or demonstrate variable expressivity, depending on the specific chromosomal anomaly. With the advent of fluorescence in situ hybridization (FISH), array-based comparative genomic hybridization, and next-generation DNA sequencing, more detailed molecular diagnoses are possible than in years past, enabling refined characterization of the genotype-phenotype correlation for subjects with 2q37 deletions. In addition, investigations into molecular and gene expression networks are expanding in neurodevelopmental conditions, and we surveyed HDAC4 downstream gene expression by quantitative real-time polymerase chain reaction, further implicating HDAC4 in its role in the regulation of RAI1. Correlation of clinical data defining the impact on downstream gene expression and the potential clinical associations across neurodevelopment will improve our understanding of these complex conditions and potentially lead to common therapeutic approaches.

35-Year Follow-Up of a Case of Ring Chromosome 2: Array-CGH Analysis and Literature Review of the Ring Syndrome

Côté et al. [1981] suggested that ring chromosomes with or without deletions share a common pattern of phenotypic anomalies, regardless of which chromosome is involved. The phenotype of this 'general ring syndrome' consists of growth failure without malformations, few or no minor anomalies, and mild to moderate mental retardation. We reconsidered the ring chromosome 2 case previously published by Côté et al. [1981], and we characterized it by array CGH, polymorphic markers as well as subtelomere MLPA and FISH analysis. A terminal deletion (q37.3qter) of maternal origin of the long arm of the ring chromosome 2 was detected and confirmed by all the above-mentioned methods. Ring chromosome 2 cases are exceedingly rare. Only 18 cases, including the present one, have been published so far, and our patient is the longest reported survivor, with a 35-year follow-up, and the third case characterized by array-CGH analysis.

Brief report: peculiar evolution of autistic behaviors in two unrelated children with brachidactyly-mental retardation syndrome

Brachidactyly-Mental Retardation (BDMR) Syndrome (MIM 600430) is associated with terminal deletions at chromosome 2q37 and a limited number of studies also reported an association between 2q37 → qter deletion and autism. Herein we describe two cases of autism in unrelated children with BDMR Syndrome, showing physical, cognitive, behavioral, and disease natural history homologies, with a very prominent social impairment in the first 4 years of life. At follow-up evaluations, spanning a 5-years period, both children experienced a progressive reduction of the autistic symptoms, besides retaining compromised cognitive ability. This report supports the hypothesis that genes in the 2q37 region may contribute to the etiology of autism, leading, however, to a peculiar evolution of the disease, with symptoms severity decreasing over time.

Deletion 2q37: an identifiable clinical syndrome with mental retardation and autism

Terminal deletion of the long arm of chromosome 2 is a rare chromosomal disorder characterized by low birth weight, delayed somatic and mental development, craniofacial defects, short neck, heart and lung congenital defects, and autistic features. We report on a girl with 46,XX.ish del(2)(q37.1) de novo karyotype, mental retardation, dysmorphic features, gastrointestinal anomalies, and autistic traits and compare her clinical manifestations with patients with the same deletion previously described in literature.

Chromosome 2q37 deletion: clinical and molecular aspects

Terminal deletions of chromosome 2 with breakpoints at or within band 2q37, ranging from visible abnormalities to cryptic, subtelomeric deletions, have been recognized with increasing frequency among children with mild-moderate mental retardation, characteristic facial appearance, and behavioral manifestations which often place them on the autism spectrum. The stereotypic facial characteristics include prominent forehead, thin, highly arched eyebrows, depressed nasal bridge, full cheeks, deficient nasal alae and prominent columella, thin upper lip, and various minor anomalies of the pinnae. Abnormal nipples, including inverted nipples, have been reported in a number of cases. CNS, ocular, cardiac, gastrointestinal, renal, and other GU anomalies have been noted in nearly one-third of patients. Of note, coarctation or hypoplasia of the aorta has been described in several affected children. Wilms tumor, renal dysplasia, and tracheomalacia have been reported only with the most proximal breakpoint at band 2q37.1 while a range of GI anomalies, pyloric stenosis, and diaphragmatic defects have been reported with breakpoints throughout the region. A subset of patients with the most distal deletion present phenotypic features which mimic Albright hereditary osteodystrophy (AHO). In addition to the AHO-like phenotype, later onset findings include seizures and cystic kidneys. Timely diagnosis of this recognizable syndrome provides a basis for genetic counseling, appropriate surveillance, and intervention, and avoids unnecessary and expensive diagnostic testing.

Disruption of diacylglycerol kinase delta (DGKD) associated with seizures in humans and mice

We report a female patient with a de novo balanced translocation, 46,X,t(X;2)(p11.2;q37)dn, who exhibits seizures, capillary abnormality, developmental delay, infantile hypotonia, and obesity. The 2q37 breakpoint observed in association with the seizure phenotype is of particular interest, because it lies near loci implicated in epilepsy in humans and mice. Fluorescence in situ hybridization mapping of the translocation breakpoints showed that no known genes are disrupted at Xp11.2, whereas diacylglycerol kinase delta (DGKD) is disrupted at 2q37. Expression studies in Drosophila and mouse suggest that DGKD is involved in central nervous system development and function. Electroencephalographic assessment of Dgkd mutant mice revealed abnormal epileptic discharges and electrographic seizures in three of six homozygotes. These findings implicate DGKD disruption by the t(X;2)(p11.2;q37)dn in the observed phenotype and support a more general role for DGKD in the etiology of seizures.

Molecular delineation of deletions on 2q37.3 in three cases with an Albright hereditary osteodystrophy-like phenotype

A minority of the reported cases of terminal 2q37 deletion clinically resemble Albright hereditary osteodystrophy (AHO)/pseudopseudohypoparathyroidism and have only mild-to-moderate mental retardation. Our molecular and cytogenetic fluorescence in situ hybridization (FISH) findings on an additional three patients further reduce the size of the minimal critical region deleted in this syndrome to about 3 Mb. This region includes the G-protein-coupled receptor 35 (GPR35), glypican 1 (GPC1), and serine/threonine protein kinase 25 (STK25) genes on 2q37.3. We have further defined several polymorphic variants within the coding region and flanking regions of GPR35 gene, which could potentially be useful for rapid detection of GPR35 gene deletion. We postulate that the absence of GPR35 may, at least partly, account for the phenotypic resemblance to the AHO. We also believe that the deletion of GPR35 could be responsible for the entity brachydactyly mental retardation syndrome (OMIM #600430), which was coined based on the above minority of patients with terminal 2q37 deletion. We recommend that every patient with AHO phenotype should undergo 2q subtelomeric FISH screen and subsequently a molecular study on the GPR35 gene. GPC1 and/or STK25 haploinsufficiency may also contribute to the AHO-like phenotype.

Molecular cytogenetic analysis of five 2q37 deletions: refining the brachydactyly candidate region

Deletions of the 2q37 region are associated with a recognizable pattern of MCA/MR so-called the AHO-like syndrome. Brachydactyly is a variable but characteristic feature of this clinical entity. Here we report on five cases of cytogenetically visible de novo deletions of this 2q37 chromosome region. Using FISH, we characterized at the molecular level the breakpoints of these deletions using a set of 15 BACs, PACs and YACs. In four patients, terminal deletions of variable size ranged between 6.2 and 10 Mb. The fifth patient had an interstitial deletion with an AHO-like phenotype including brachydactyly. These findings when compared to previous observations allowed us to narrow down the brachydactyly critical region between BACs RP11-585E12 and RP11-351E10. It contains HDAC4 and STK25 candidate genes loci.

Evaluation of the chromosome 2q37.3 gene CENTG2 as an autism susceptibility gene

Autism is a highly heritable neurodevelopmental syndrome with a complex genetic etiology for which no disease genes have yet been definitively identified. We ascertained three subjects with autism spectrum disorders and chromosome 2q37.3 terminal deletions, and refined the deletion breakpoint regions using polymorphism mapping and fluorescence in situ hybridization (FISH) probes. We then genotyped polymorphic markers downstream from the breakpoint region in a sample of autism affected sibling pair families. Both the chromosomal breakpoints and linkage analyses focused our attention on the gene centaurin gamma-2 (CENTG2), an attractive candidate gene based also on its function and pattern of expression. We therefore assessed CENTG2 for its involvement in autism by (1) screening its exons for variants in 199 autistic and 160 non-autistic individuals, and (2) genotyping and assessing intra-genic polymorphisms for linkage and linkage disequilibrium (LD). The exon screen revealed a Ser --> Gly substitution in one proband, an Arg --> Gly substitution in another, and a number of additional variants unique to the autism families. No unique variants were found in the control subjects. The genotyping produced strong evidence for linkage from two intronic polymorphisms, with a maximum two-point HLOD value of 3.96 and a posterior probability of linkage (PPL) of 51%. These results were contradicted, however, by substantially weaker evidence for linkage from multi-point analyses and by no evidence of LD. We conclude, therefore, that 2q37.3 continues to be a region of interest for autism susceptibility, and that CENTG2 is an intriguing candidate gene that merits further scrutiny for its role in autism.

Chromosome 2q terminal deletion: report of 6 new patients and review of phenotype-breakpoint correlations in 66 individuals

We report a new patient with terminal deletion of chromosome 2 with breakpoint at 2q36 and five additional new patients with 2q terminal deletion with breakpoint at 2q37. Hemidiaphragmatic hernia is a novel finding in one patient with a breakpoint at 2q37.1. In comparing these patients to 60 previously reported individuals with 2q terminal deletions, certain physical abnormalities are loosely associated with positions of breakpoint. For example, facial features (e.g., prominent forehead, depressed nasal bridge, and dysmorphic ears and nose), short stature, and short hands and feet were frequent in patients with breakpoints at or proximal to 2q37.3. Reports of horseshoe kidney and Wilms tumor were limited to patients with a breakpoint at 2q37.1, and structural brain anomalies and tracheal anomalies were reported only in patients with breakpoints at or proximal to 2q37.1. Cleft palate was reported only in patients with the most proximal breakpoints (2q36 or 2q35). Neurological effects including developmental delay, mental retardation, autistic-like behavior, and hypotonia were typical in this patient population but did not stratify in severity according to breakpoint. Terminal deletion of the long arm of chromosome 2 should be considered in the infant with marked hypotonia, poor feeding, gastroesophageal reflux, and growth delay, and the older child with developmental delay, autistic behavior, and the characteristic facial and integumentary features described herein. Assignment of clinical features to specific breakpoints and refinement of predictive value may be useful in counseling.

Molecular characterization of a cryptic 2q37 deletion in a patient with Albright hereditary osteodystrophy-like phenotype

The Albright hereditary osteodystrophy-like (AHO-like) syndrome was recently defined as a rare dysmorphic syndrome including brachymetaphalangism and mental retardation. This phenotype occurs in Albright hereditary osteodystrophy (AHO) but unlike it, the level of the Gs alpha protein activity is not reduced. To date 59 patients with these clinical and biochemical features have been reported, and for the majority of them (57/59) a cytogenetically visible 2q37 deletion has been observed. We report a new case of typical AHO-like syndrome with normal karyotype. Using the polymorphic marker D2S125 we found a loss of heterozygosity suggestive of a de novo 2q37 deletion of maternal origin. This hypothesis was confirmed by FISH analysis with a subtelomeric 2q probe containing the D2S90 marker. Genotypic analysis allowed us to map the proximal breakpoint of the subtelomeric deletion within an interval delimited by D2S2338 (present) and D2S2253 (deleted). This 2q subtelomeric deletion as small as 4 Mb is to date the smallest one observed in association with a typical AHO-like phenotype, and allows us to move the centromeric boundary of the AHO-like critical region by 750 kb towards the 2q telomere.

Familial cryptic translocation (2;17) ascertained through recurrent spontaneous abortions

We report a young woman who presented with a reproductive history of three recurrent spontaneous abortions (RSA) and two neonatal deaths. Comparative genomic hybridization (CGH) was used to determine the chromosomal composition of the patient's last miscarriage. It showed the presence of monosomy for the distal end of chromosome 2 long arm (segment 2q37.2 to qter) and trisomy for the distal end of chromosome 17 long arm (segment 17q25 to qter). The mother was found to be a carrier for a cryptic translocation between chromosomes 2 and 17 long arms by fluorescence in situ hybridization using a subtelomeric probe for 17q. Retrospective CGH analysis on one baby who died neonatally showed that he had inherited the maternal translocation in the same unbalanced state as the last pregnancy loss. His detailed postmortem examination is reported.

Recombinants of intrachromosomal transposition of subtelomeres in chromosomes 1 and 2: a cause of minute terminal chromosomal imbalances

Two cases of submicroscopic recombinants of intrachromosomal transposition of telomeres, one each from chromosome 1 and 2 are described. Meiotic crossing-over would generate the recombinants from these reciprocal rearrangements. In both cases, which were detected by FISH with subtelomeric probes, there is a minute deletion of the qter region and a second presence of the pter subtelomeric region on the respective qter, i.e., a duplication of 1pter or 2pter respectively. The deletion on 2qter (case 2) was confirmed by microsatellite inheritance and was of paternal origin, but in case 1 there was no detectable 1q deletion other than of the subtelomeric probe, and parental origin could not be determined. The present case 2 with del(2qter)/dup(2pter) shares many features with reported cases of simple deletion (2qter) but did not have features of Albright hereditary osteodystrophy, which are seen in half of such deletion patients. The clinical features present in case 1 were similar to those of the previously reported case of a submicroscopic 1qter deletion but also to cases with microscopically visible 1qter deletions, presumably because of gene enrichment in subtelomeric regions. Recombinants of such intrachromosomal subtelomere transpositions detected by subtelomeric probes may comprise up to 10% of submicroscopic pter or qter deletion cases. Other cases of this unusual mechanism may be detected with more common use of subtelomeric probes. It is suggested the bouquet associations of telomeres in early meiosis may facilitate such unusual rearrangements.

Ring 2 chromosome: ten-year follow-up report

Côté et al. [1981: Ann Genet 24:231-235] suggested that ring chromosomes without a preceding deletion share a common pattern of phenotypic anomalies, independent of what chromosome is involved. The phenotype of such a "general ring syndrome" consists of growth failure without malformations, few or no minor anomalies, and mild-to-moderate mental retardation. We report on a patient with a ring 2 chromosome with features suggestive of Silver-Russell syndrome at birth and striking postnatal growth retardation with minor intellectual involvement supporting Côté's suggestion. This would be the ninth case of ring 2 chromosome published; the patient is the longest reported survivor, with a 10-year follow-up.

Microdeletion of chromosome sub-band 2q37.3 in two patients with abnormal situs viscerum

We report on two cases of microdeletion of chromosome sub-band 2q37.3 with abnormal situs viscerum. The first patient had dextrocardia, duodenal and jejunal atresia, and an abdominal hernia. The liver was in the left upper quadrant, stomach in the right upper quadrant. In contrast anema the ascending colon was in the left, and descending colon on the right, with an area of atresia in the mid-jejunum. The second patient had malrotation and malposition of large and small bowel, with most of the bowels positioned above the liver and spleen. There was incomplete rotation of the cecum. The right kidney was malrotated and mal-positioned. The finding of 2q37.3 deletion in both patients implies that a locus or loci involved in the development of normal body situs lies within this chromosome region. Molecular cytogenetic evaluation for a possible 2q37.3 deletion should be considered in patients with abnormal situs viscerum.

RDCI, the vasoactive intestinal peptide receptor: a candidate gene for the features of Albright hereditary osteodystrophy associated with deletion of 2q37

Albright hereditary osteodystrophy (AHO) is an autosomal dominant disorder characterised by the presence of brachymetaphalangism, short stature, obesity, and mental retardation. Variable biochemical changes many represent either pseudohypoparathyroidism (PHP) owing to resistance to parathormone (PTH) or pseudopseudohypoparathyroidism (PPHP) with no hormone resistance. In most cases of AHO, reduced levels of Gs alpha have been found and a number of deactivating mutations in the gene for Gs alpha located on chromosome 20q13 have been described. Recently a number of people with an AHO-like phenotype have been reported in whom a deletion of chromosomal region 2q37 has been found in the absence of biochemical abnormalities or a reduction in Gs alpha activity. We present a further female patient with a cytogenetically visible deletion of 2q37, an AHO-like phenotype, and unusual biochemistry suggesting moderate PTH resistance. The vasoactive intestinal peptide receptor (RDCI) has recently been mapped to 2q37 and we propose that this is a candidate gene, hemizygosity of which affects signal transduction and leads to the AHO-like phenotype found in patients with 2q37 deletions.

Small interstitial deletion of the long arm of chromosome 2 (2q24.3): further delineation of 2q medial monosomy syndrome

We report on a female infant with an interstitial deletion involving 2q24.3. She had multiple congenital anomalies similar to those in patients with del(2)(q31q33) except for an occipital encephalocele. As a result of comparison of clinical findings among interstitial 2q deletions, a distinct 2q medial monosomy syndrome may be delineable in association with a deletion of 2q31.

Deletion or triplication of the alpha 3 (VI) collagen gene in three patients with 2q37 chromosome aberrations and symptoms of collagen-related disorders

Two new cases of del(2)(q37.1) and one case of partial trp(2)(q37) are studied by FISH with cosmid probes from the COL6A3 and PAX3 genes mapped in 2q37.3 and 2q36, respectively. While the PAX3 gene dosage appeared unaffected, the COL6A3 gene was found to be deleted and triplicated, respectively. This finding could explain features of connective tissue disorders such as joint laxity and hypotonia or joint stiffness and epiphyseal dysplasia, particularly documented by congenital dislocation of the radial head. Karyotype-phenotype correlations with reference to published cases are discussed.

Albright hereditary osteodystrophy and del(2) (q37.3) in four unrelated individuals

Albright hereditary osteodystrophy (AHO) is a condition with characteristic physical findings (short stature, obesity, round face, brachydactyly) but variable biochemical changes (pseudohypoparathyroidism, pseudopseudohypoparathyroidism). Most patients with AHO have decreased activity of the guanine nucleotide-binding protein (GS protein) that stimulates adenylyl cyclase. The gene encoding the alpha subunit of the GS protein (GNAS1) has been mapped to the long arm of chromosome 20. We describe 4 unrelated individuals with apparent AHO, associated with small terminal deletions of chromosome 2. All 4 patients had normal serum calcium levels consistent with pseudopseudohypoparathyroidism. Del(2) (q37) is the first consistent karyotypic abnormality that has been documented in AHO [Phelan et al., 1993: Am J Hum Genet 53:484]. The finding of the same small terminal deletion in 4 unrelated individuals with a similar phenotype suggests that a gene locus in the 2q37 region is important in the pathogenesis of Albright syndrome. The association of Albright syndrome and the GNAS1 locus on chromosome 20 is well documented. The observation of a second potential disease locus on chromosome 2 may help explain the heterogeneity observed in this disorder.