Terminal 2q deletion--a recognizable syndrome

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.

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.