Chromosome 14 deletions, rings, and epilepsy genes: A riddle wrapped in a mystery inside an enigma

The ring 14 syndrome is a rare condition caused by the rearrangement of one chromosome 14 into a ring-like structure. The formation of the ring requires two breakpoints and loss of material from the short and long arms of the chromosome. Like many other chromosome syndromes, it is characterized by multiple congenital anomalies and developmental delays. Typical of the condition are retinal anomalies and drug-resistant epilepsy. These latter manifestations are not found in individuals who are carriers of comparable 14q deletions without formation of a ring (linear deletions). To find an explanation for this apparent discrepancy and gain insight into the mechanisms leading to seizures, we reviewed and compared literature cases of both ring and linear deletion syndrome with respect to both their clinical manifestations and the role and function of potentially epileptogenic genes. Knowledge of the epilepsy-related genes in chromosome 14 is an important premise for the search of new and effective drugs to combat seizures. Current clinical and molecular evidence is not sufficient to explain the known discrepancies between ring and linear deletions.

A novel 14q13.1-21.1 deletion identified by CNV-Seq in a patient with brain-lung-thyroid syndrome, tooth agenesis and immunodeficiency

Background

Chromosome 14q11-q22 deletion syndrome (OMIM 613457) is a rare genomic disorder. The phenotype heterogeneity depends on the deletion size, breakpoints and genes deleted. Critical genes like FOXG1, NKX2–1, PAX9 were identified.

Case presentation

We performed whole exome sequencing (WES) and copy number variation sequencing (CNV-seq) for a patient with mild speech and motor developmental delay, short stature, recurrent pulmonary infections, tooth agenesis and triad of brain-lung-thyroid syndrome. By using CNV-seq, we identified a 3.1 Mb de novo interstitial deletion of the 14q13.2q21.1 region encompassing 17 OMIM genes including NKX2–1, PAX9 and NFKBIA. Our patient’s phenotype is consistent with other published 14q13 deletion patients.

Conclusion

Our results showed the combination of WES and CNV-seq is an effective diagnostic strategy for patients with genetic or genomic disorders. After reviewing published patients, we also proposed a new critical region for 14q13 deletion syndrome with is a more benign disorder compared to 14q11-q22 deletion syndrome.

Child Neurology: Siblings with infantile epilepsy and developmental delay

Objective

Chromosome 14q11-q22 deletion syndrome (OMIM 613457) is a rare genomic disorder with a variable phenotype.

Methods

We report 2 full siblings, a brother and sister, with a unique familial 2.4 Mb microdeletion at 14q13.1–14q13.3 by microarray (first identified in the brother, Mayo Clinical Laboratories, 2010).

Results

Both children presented with infantile spasms that evolved to intractable epilepsy and profound developmental delay. They share distinctive dysmorphic features: long expressionless facies, full cheeks, flattened midface, full lips, and generalized hypotonia. Only the sister has hemophagocytic lymphohistiocytosis (HLH). Testing in the brother revealed 3 variants of unknown significance (VUS) (Greenwood Genetics, epilepsy/seizure panel, 145 genes, 2015). The sister had normal results with a different gene panel (GeneDx, infantile epilepsy panel, 75 genes, 2016) but it did not include the 3 genes in which VUS were identified in her brother. Whole exome sequencing in the mother, father, and both siblings was negative without VUS (GeneDx, XomeDx, 2016). There were no variants within the deleted interval in the intact allele for both children. Parental fluorescent in situ hybridization studies for 14q13.1–14q13.3, done in 2017, were normal. Haplotype analysis of the intact chromosome 14 in the sister supported paternal origin for the deletion and likely germline mosaicism in the father. Haploinsufficiency of genes in the deleted region has not been associated with an abnormal phenotype.

Conclusions

These children have a specific, recognizable neurodevelopmental phenotype and 14q13 microdeletion. This report highlights the challenges of coordinating and interpreting genetic testing in syndromic epilepsy.

A Rare Chromosomal Disorder – 14q Interstitial Deletion Syndrome

Introduction: Interstitial deletions of the long arm of chromosome 14q (OMIM 613457) are very rare conditions.

Case presentation: We present a 3-month-old male patient with dysmorphic features and congenital heart defect associated with a small interstitial deletion of chromosome 14q, identified by cytogenetic analysis as 46,XY,del(14)(q11q12). Dysmorphic features included microcephaly, broad nasal bridge, micrognathia, large and poorly folded auricular lobes and long digits. He also present rectus abdominis diastasis and umbilical hernia. The cranial computer tomography showed partial agenesis of the corpus callosum and ventriculomegaly.

Conclusions: Cytogenetic analysis or molecular techniques are necessary to establish the correct diagnosis in patients with multiple congenital anomalies in association with proximal or distal interstitial 14q deletion.

Neurological features of 14q24-q32 interstitial deletion: report of a new case

Background

Interstitial deletions of the long arm of chromosome 14 involving the 14q24-q32 region have been reported in less than 20 patients. Previous studies mainly attempted to delineate recognizable facial dysmorphisms; conversely, descriptions on neurological features are limited to the presence of cognitive and motor delay, but no better characterization exists.

Case presentation

In this paper we report on a patient with a de novo interstitial deletion of 5.5 Mb at 14q24.3-q31.1. The deletion encompasses 84 genes, including fourteen Mendelian genes. He presented with dysmorphic face, developmental delay, paroxysmal non-epileptic events and, subsequently, epilepsy.

Conclusions

The clinical and molecular evaluation of this patient and the review of the literature expand the phenotype of 14q23-q32 deletion syndrome to include paroxysmal non-epileptic events and infantile-onset focal seizures.

Morphometric variability of neuroimaging features in children with agenesis of the corpus callosum

Background

Agenesis of the corpus callosum (ACC) is a developmental brain malformation associated with a wide spectrum of structural brain abnormalities and genetic loci. To characterize the diverse callosal morphologies and malformations of brain development associated with ACC, we report on the neuroimaging findings of 201 individuals diagnosed with corpus callosal abnormalities.

Methods

We searched through medical records of individuals seen at New York Presbyterian Hospital between 2002 and 2013 and thought to have ACC. We confirmed 201 individuals meeting criteria and used magnetic resonance imaging to characterize morphological variants of the corpus callosum and associated brain malformations.

Results

The majority of individuals displayed hypoplasia or dysplasia of the corpus callosum (N = 160, 80 %). Forty-one (20 %) displayed complete agenesis of the corpus callosum with other abnormalities, while only 18 (9 %) displayed complete agenesis without associated brain abnormalities. White matter abnormalities were more frequent in hypoplasia or dysplasia group than complete agenesis (28.2 % vs 9.8 %, p < 0.05). In contrast, hippocampal abnormalities, colpocephaly, and Probst bundles were significantly more frequent in complete agenesis compared to hypoplasia or dysplasia group.

Conclusions

Collectively, our results underscore the broad diversity of morphological variants of the corpus callosum and associated brain abnormalities in individuals with ACC.

Platelet defects in congenital variant of Rett syndrome patients with FOXG1 mutations or reduced expression due to a position effect at 14q12

The Forkhead box G1 (FOXG1) gene encodes a transcriptional repressor essential for early development of the telencephalon. Intragenic mutations and gene deletions leading to haploinsufficiency cause the congenital variant of Rett syndrome. We here describe Rett syndrome-like patients, three of them carrying a balanced translocation with breakpoint in the chromosome 14q12 region, and one patient having a 14q12 microdeletion excluding the FOXG1 gene. The hypothesis of long-range FOXG1-regulatory elements in this region was supported by our finding of reduced FOXG1 mRNA and protein levels in platelets and skin fibroblasts from these cases. Given that FOXG1 is not only expressed in brain but also in platelets, we have studied platelet morphology in these patients and two additional patients with FOXG1 mutations. Electron microscopy of their platelets showed some enlarged, rounder platelets with often abnormal alpha, and fewer dense granules. Platelet function studies were possible in one 14q12 translocation patient with a prolonged Ivy bleeding time and a patient with a heterozygous FOXG1 c.1248C>G mutation (p.Tyr416X). Both have a prolonged PFA-100 occlusion time with collagen and epinephrine and reduced aggregation responses to low dose of ADP and epinephrine. Dense granule ATP secretion was normal for strong agonists but absent for epinephrine. In conclusion, our study shows that by using platelets functional evidence of cis-regulatory elements in the 14q12 region result in reduced FOXG1 levels in patients' platelets having translocations or deletions in that region. These platelet functional abnormalities deserve further investigation regarding a non-transcriptional regulatory role for FOXG1 in these anucleated cells.