Epilepsy panels in clinical practice: Yield, variants of uncertain significance, and treatment implications

OBJECTIVE

There has been increasing utilization of genetic testing for pediatric epilepsy in recent years. Little systematic data is available examining how practice changes have impacted testing yields, diagnostic pace, incidence of variants of uncertain significance (VUSs), or therapeutic management.

METHODS

A retrospective chart review was performed at Children's Hospital Colorado from February 2016 through February 2020. All patients under 18 years for whom an epilepsy gene panel was sent were included.

RESULTS

A total of 761 epilepsy gene panels were sent over the study period. During the study period, there was a 292% increase in the average number of panels sent per month. The time from seizure onset to panel result decreased over the study period from a median of 2.9 years to 0.7 years. Despite the increase in testing, the percentage of panels yielding a disease-causing result remained stable at 11-13%. A total of 90 disease-causing results were identified, > 75% of which provided guidance in management. Children were more likely to have a disease-causing result if they were < 3 years old at seizure onset (OR 4.4, p < 0.001), had neurodevelopmental concerns (OR 2.2, p = 0.002), or had a developmentally abnormal MRI (OR 3.8, p < 0.001). A total of 1417 VUSs were identified, equating to 15.7 VUSs per disease-causing result. Non-Hispanic white patients had a lower average number of VUSs than patients of all other races/ethnicities (1.7 vs 2.1, p < 0.001).

SIGNIFICANCE

Expansion in the volume of genetic testing corresponded to a decrease in the time from seizure onset to testing result. Diagnostic yield remained stable, resulting in an increase in the absolute number of disease-causing results annually-most of which have implications for management. However, there has also been an increase in total VUSs, which likely resulted in additional clinical time spent on VUS resolution.

HGG-17. Novel Fusion in Congenital Brainstem Diffuse High-Grade Glioma

BACKGROUND: Infant-type hemispheric glioma, previously termed infantile glioblastoma multiforme, is a rare infantile neoplasm with improved survival and distinct molecular features when compared to other pediatric and adult-type high-grade glioma. Infant-type high-grade gliomas are typically located in the cerebral hemispheres and are characterized by ALK, ROS1, MET, and NTRK fusions. Typical brainstem gliomas (diffuse midline glioma, H3 K27-altered or diffuse intrinsic pontine glioma) are comparatively rare in this age group. As a result, the biology of brainstem congenital high-grade gliomas is poorly described. RESULTS: A 3 month old female who initially presented with failure to thrive had an apneic event and was found to have an infiltrative mass in the medulla with expansion into the pons and cervical spine on magnetic resonance imaging. She underwent surgical biopsy with pathology revealing diffuse high-grade glioma, WHO grade 4. Next generation sequencing showed no alterations to H3F3A, IDH, or fusions involving BRAF, ALK, ROS1, MET, or NTRK. Whole-transcriptome sequencing revealed a novel fusion of PDGFRB:APOBEC3C. She received chemotherapy with 2 cycles of carboplatin/etoposide and 2 cycles of carboplatin/etoposide/imatinib before having disease progression. She then underwent palliative radiation (35 Gy in 10 fractions) with near complete regression of her disease. Surprisingly, our patient has not had any progression of disease or new lesions now two years from her last therapy. CONCLUSION: Congenital high-grade glioma is a rare, unique entity that greatly differs from its adult and childhood counterparts. Here, we discuss a previously-unreported fusion of PDGFB:APOBEC3C in a patient with congenital brainstem diffuse high-grade glioma with a favorable clinical course. This highlights the importance of routine molecular characterization, both to better understand the complex biology of this rare disease and to guide prognosis and clinical decision making for individual patients and families.

N-terminus DUX4-immunohistochemistry is a reliable methodology for the diagnosis of DUX4-fused B-lymphoblastic leukemia/lymphoma (N-terminus DUX4 IHC for DUX4-fused B-ALL)

B-lymphoblastic leukemia/lymphoma (B-ALL) is the most common pediatric malignancy and the most commonly diagnosed adult lymphoblastic leukemia. Recent advances have broadened the spectrum of B-ALL, with DUX4 gene fusions implicated in a subclass occurring in adolescents and young adults and harboring a favorable prognosis. DUX4 fusions have been challenging to identify. We aimed to determine whether expression of the DUX4 oncoprotein, as detected by targeted immunohistochemistry, might serve as a surrogate for molecular detection of DUX4 fusions in B-ALL. A cohort of investigational B-ALLs was generated with enrichment for DUX4 fusions by inclusion of cases with characteristic demographic features and immunophenotypic properties. B-ALLs with mutually exclusive cytogenetics were collected. Immunohistochemical staining by a monoclonal antibody raised against the N-terminus of the DUX4 protein was performed. N-DUX4 immunohistochemistry demonstrated strong, crisp nuclear staining in blasts of seven investigational cases, six of which had nucleic acid material available for molecular evaluation. Five of these cases demonstrated RNA-seq DUX4-fusion positivity. One N-DUX4 immunohistochemistry positive case lacked a definitive DUX4-fusion by RNA-seq, though demonstrated a gene expression profile characteristic of DUX4-rearranged B-ALLs, a CD2+ immunophenotype, and a lack of staining by C-terminus DUX4 antibody immunohistochemistry. At least 83.3% [5/6] positive predictive value. N-DUX4 immunohistochemistry was negative in blasts of three RNA-seq DUX4-fusion negative cases (3/3; 100% negative predictive value). B-ALLs with mutually-exclusive cytogenetic profiles were all N-DUX4 negative (0/10, specificity 100%). N-DUX4 immunohistochemistry is reliable for the distinction of DUX4-rearranged B-ALLs from other B-ALLs. We recommend its use for subclassification of B-ALLs in adolescents and young adults and in B-ALLs that remain "not otherwise specified." This article is protected by copyright. All rights reserved.

A new blood group system, RHAG: three antigens resulting from amino acid substitutions in the Rh-associated glycoprotein

BACKGROUND AND OBJECTIVES

Rh-associated glycoprotein (RhAG) is closely associated with the Rh proteins in the red cell membrane. Two high frequency antigens (Duclos and DSLK) and one low frequency antigen (Ol(a)) have serological characteristics suggestive of expression on RhAG.

MATERIALS AND METHODS

RHAG was sequenced from the DNA of one Duclos-negative, one DSLK-negative, and two Ol(a+) individuals. Recombinant protein was expressed in HEK 293 cells. Protein models with RhAG subunits were constructed.

RESULTS

The original Duclos-negative patient was homozygous for RHAG 316C>G, encoding Gln106Glu. HEK 293 cells expressing Gln106Glu mutant RhAG did not react with anti-Duclos. An individual with DSLK-negative red cells was homozygous for 490A>C, encoding Lys164Gln. Two Ol(a+) members of the original Norwegian family were heterozygous for 680C>T, encoding Ser227Leu. A Japanese donor with Rh(mod) phenotype had Ol(a+) red cells and was homozygous for 680C>T.

CONCLUSION

The three red cell antigens encoded by RHAG form the RHAG blood group system: Duclos is RHAG1 (030001); Ol(a) is RHAG2 (030002); and DSLK is provisionally RHAG3 (030003).

Direct optometrist referral of cataract patients into a pilot 'one-stop' cataract surgery facility

OBJECTIVES

To determine the feasibility of a) direct optometrist referral of patients with cataract, and b) combined assessment with same day cataract surgery ('one stop' cataract surgery).

METHODS

Evaluation of 169 patients referred directly by optometrists into a pilot 'one stop' cataract surgery facility.

RESULTS

Of 169 referrals, 160 patients (94.7%) were given confirmed appointments for the 'one stop' cataract service and 9 patients (5.3%) were appointed conventionally. Of 160 patients attending the 'one stop' cataract service, 154 patients (96.3%) underwent cataract surgery at the same visit, in 4 patients (2.5%) cataract surgery was indicated but deferred and in 2 patients (1.3%) cataract surgery was not indicated. The referral was supplemented with information regarding the patient's medical history forwarded by the general practitioner for 3 patients (1.8%). There were no systemic or sight-threatening complications. 151 patients (98.1%) achieved a visual acuity of 6/12 or better at a mean of 31 days post-operatively.

CONCLUSION

Optometrists can accurately predict the need for cataract surgery and refer directly into a pilot 'one stop' cataract surgery facility, without the need for general practitioner involvement. 'One stop' cataract surgery is feasible; benefits to the patient include the abolition of the need to visit the general practitioner for consultation and referral, and the hospital for pre-assessment.

Novel word acquisition in children with Down syndrome: does modality make a difference?

Signing is a commonly used intervention technique for children with cognitive impairments who have expressive language delays. Novel word learning in three conditions (signed only, spoken only, signed and spoken combined) was compared for children with Down syndrome (2;1 to 5;2) and mental-age matched control children (1;4 to 2;6). Spontaneous imitations and responses to production and comprehension probes were examined after 5, 10, and 15 word exposures. No group differences in frequency of imitations or productions were obtained. The frequency of imitations was highest in the combined condition. Probed productions were infrequent, although novel words were produced most often in spoken and combined conditions. For both imitated and probed productions in the combined condition, the spoken portion was almost exclusively produced. Across conditions, children with Down syndrome comprehended fewer words than did control children. The evidence for and explanations of the facilitative effect of signs and the advantage of dual-method presentation are discussed.

Solution structure of the hRPABC14.4 subunit of human RNA polymerases

The protein hRPABC14.4 is an essential subunit of human RNA polymerases I, II, and III and is required for the transcription of all human nuclear genes. The structure of hRPABC14.4 was determined by nuclear magnetic resonance spectroscopy. The protein fold comprises a highly conserved central domain forming two antiparallel alpha-helices flanked by the less conserved N- and C-terminal regions forming a five-stranded beta-sandwich. Amino acids from the two helices participate in the generation of a hydrophobic surface area which is conserved in all eukaryotic and archaeal homologous subunits, and likely constitutes a critical macromolecular interaction interface. The hRPABC14.4 structure accounts for mutagenesis results in Saccharomyces cerevisiae and provides a structural working model for elucidating the role of this subunit in the molecular architecture and function of the human nuclear RNA polymerases.

Characterization and chromosomal localization of PTP-NP-2, a new isoform of protein tyrosine phosphatase-like receptor, expressed on synaptic boutons

Recently, there have been several reports describing the cloning and characterization of the novel family of protein tyrosine phosphatase-like receptor molecules (known as IA-2 and PTP-NP/PTP-IAR/IA-2beta/phogrin), which may act as autoantigens in diabetes. Here, we report the molecular characterization and chromosomal localization of a new isoform of this family in brain termed PTP-NP-2 (for PTP-NP tyrosine phosphatase isoform), and its function in rat primary hippocampal neurons. PTP-NP-2 has 48% identity to IA-2. The principal difference between PTP-NP-2 and PTP-NP is a 17-amino-acid insert near the N-terminus of PTP-NP that is absent in PTP-NP-2. Genomic DNA analysis indicates that the 17-amino-acid insert is coded by a separate exon, suggesting that both IA-2beta and PTP-NP-2 are isoforms arising by alternate splicing of the same gene. Reverse transcriptase-PCR revealed that both isoforms are present in human SH-SY5Y neuroblastoma cells. PTP-NP-2 mRNA expression is highly restricted, with a 5.5-kb specific transcript in human fetal and adult brain and 5.5 and 3. 8 kb in human adult pancreas. SH-SY5Y neuroblastoma and U87-MG glioblastoma cells showed specific transcripts of 5.5 and 3.8<HSP SP = "0.25">kb, respectively, indicating the existence of several isoforms of this molecule in the nervous system. The human gene encoding PTP-NP-2 was assigned to human chromosome 7q22-qter using Southern blot analysis of genomic DNAs from rodent/human somatic hybrid cell lines. Confocal microscopy analyses of rat primary hippocampal neurons revealed that PTP-NP-2 is abundantly expressed on synaptic boutons in primary neurons. Wild-type PTP-NP-2 showed no measurable tyrosine phosphatase activity using an in-vitro pNPP assay. Examination of the PTP-NP-2 catalytic consensus sequence revealed that this sequence differed from the typical tyrosine phosphatase-domain consensus sequence by an alanine to aspartate change (amino acid 930). Mutation of aspartate 930 to alanine produced a catalytically active enzyme, suggesting that native PTP-NP and its isoform PTP-NP-2 are catalytically inactive receptor protein tyrosine phosphatase homologues. Taken together, these results indicate that the tyrosine phosphatase PTP-NP-2 is a new isoform of PTP-NP tyrosine phosphatase, is expressed on synaptic boutons and may participate in the regulation of synaptic bouton endocytosis.

Effect of postoperative mydriatics on the iris

PURPOSE

To assess the role postoperative mydriatics play after extracapsular cataract extraction (ECCE) and posterior chamber intraocular lens (IOL) implantation in causing iris modifications and in controlling inflammation.

SETTING

Outpatients Department, Ninewells Hospital, Dundee, Scotland.

METHODS

The prospective study comprised 136 patients who had standardized ECCE. Half the patients used a mydriatic for 2 weeks postoperatively. Anterior chamber activity, pain, and eye redness were evaluated at 2 weeks postoperatively; pupil shape, peripheral anterior synechias, IOL position, and iris adhesions, at 6 weeks.

RESULTS

Iris-lens adhesions were significantly more common in the group using a mydriatic. There was no difference between the two groups in postoperative inflammation.

CONCLUSION

Mydriatics should not be used routinely after ECCE with posterior chamber IOL implantation.

The three domains of a bacterial sialidase: a beta-propeller, an immunoglobulin module and a galactose-binding jelly-roll

BACKGROUND

Sialidases, or neuraminidases, have been implicated in the pathogenesis of many diseases, but are also produced by many non-pathogenic bacteria. Bacterial sialidases are very variable in size, often possessing domains in addition to the catalytic domain. The sialidase from the non-pathogenic soil bacterium Micromonospora viridifaciens is secreted in two forms with molecular weights of 41 kDa or 68 kDa, depending on the nature of the carbohydrate used to induce expression.

RESULTS

We report here the X-ray crystal structures of the 41 kDa and 68 kDa forms of the sialidase from M. viridifaciens at 1.8 A and 2.5 A resolution respectively. In addition, we report a complex of the 41 kDa form with an inhibitor at 2.0 A resolution, and a complex of the 68 kDa form with galactose at 2.5 A. The 41 kDa form shows the canonical sialidase beta-propeller fold. The 68 kDa form possesses two additional domains, one with an immunoglobulin-like fold that serves as a linker to the second, which is homologous to the galactose-binding domain of a fungal galactose oxidase.

CONCLUSIONS

The presence of the additional carbohydrate-binding domain in the 68 kDa form of the bacterial sialidase reported here is a further example of a combination of carbohydrate binding and cleaving domains which we observed in the sialidase from Vibrio cholerae. This dual function may be common, but only to other bacterial and parasitic sialidases, but also to other secreted glycosidases involved in pathogenesis. The bacterium may have acquired both the immunoglobulin module and the galactose-binding module from eukaryotes, as the enzyme shows a remarkable similarity to a fungal galactose oxidase which possesses similar domains performing different functions and assembled in a different order.

Dark adaptation and falls in the elderly

The human eye is capable of adjusting to wide variations in light intensity by altering the pupil size and the sensitivity of the retina to light. Falls are one of the commonest problems of old age, and the causes are multifactorial. As falls often occur at night, this study was designed to compare dark adaptation in groups of elderly fallers and non-fallers. Twenty-two female patients in a geriatric assessment ward were included in the study and classified as 'fallers' or 'non-fallers'. A full ophthalmic examination was performed on each subject, and dark adaptation measured, in a single-blind fashion, using the Friedmann visual field analyser; following initial bleaching of the retinal photoreceptors, the room was placed in total darkness and retinal sensitivity measured every minute for 20 min. The values, expressed as log filter density, were plotted against duration of time in the dark. The mean values at 5 min were 0.9 in the fallers and 1.4 in the non-fallers (p less than 0.02 unpaired t test) and at 20 min 2.2 and 3.2, respectively (p less than 0.04). These results indicate reduced retinal sensitivity and hence impaired dark adaptation in the falling group. Lighting levels in the homes of many old people have been shown to be inadequate. Impaired dark adaptation may leave an elder person virtually blind for a minute or more on moving from a bright room to a darker area. The provision of night lights in the homes of recurrent fallers may offset the influence of impaired dark adaptation.