Exploring the utility of whole‐exome sequencing as a diagnostic tool in a child with atypical episodic muscle weakness

The advent of whole‐exome next‐generation sequencing (WES) has been pivotal for the molecular characterization of Mendelian disease; however, the clinical applicability of WES has remained relatively unexplored. We describe our exploration of WES as a diagnostic tool in a 3½‐year old female patient with a 2‐year history of episodic muscle weakness and paroxysmal dystonia who presented following a previous extensive but unrevealing diagnostic work‐up. WES was performed on the proband and her two parents. Parental exome data was used to filter potential de novo genomic events in the proband and suspected variants were confirmed using di‐deoxy sequencing. WES revealed a de novo non‐synonymous mutation in exon 21 of the calcium channel gene CACNA1S that has been previously reported in a single patient as a rare cause of atypical hypokalemic periodic paralysis. This was unexpected, as the proband's original differential diagnosis had included hypokalemic periodic paralysis, but clinical and laboratory features were equivocal, and standard clinical molecular testing for hypokalemic periodic paralysis and related disorders was negative. This report highlights the potential diagnostic utility of WES in clinical practice, with implications for the approach to similar diagnostic dilemmas in the future.     

Development of Doxycycline MIC and Disk Diffusion Interpretive Breakpoints and Revision of Tetracycline Breakpoints for Streptococcus pneumoniae

A study was performed to derive susceptibility testing interpretive breakpoints for doxycycline with Streptococcus pneumoniae and to reassess breakpoints for tetracycline using the requirements defined in Clinical and Laboratory Standards Institute (CLSI) document M23-A3. Tetracycline and doxycycline MICs and disk diffusion zone sizes were determined on 189 isolates selected from the 2009-2010 CDC Active Bacterial Core surveillance strain collection according to the testing methods described in CLSI documents M07-A8 and M02-A10. Tetracycline and doxycycline MICs and zones were compared to each other directly, and the reproducibility of MICs and zone diameters for both drugs was determined. Scattergrams of tetracycline MICs versus corresponding zone diameters and doxycycline MICs versus zones were prepared, and analysis indicated that the present CLSI tetracycline MIC and disk breakpoints did not fit the susceptibility data for doxycycline. Doxycycline was 1 to 3 dilutions more potent than tetracycline, especially in strains harboring the tetM resistance determinant. tetM was detected in ≥90% of isolates having tetracycline MICs of ≥4 μg/ml and in ≥90% with doxycycline MICs of ≥1. Limited pharmacokinetic/pharmacodynamic (PK/PD) data coupled with application of the error-rate bounded method of analysis suggested doxycycline-susceptible breakpoints of either ≤0.25 μg/ml or ≤0.5 μg/ml, with intermediate and resistant breakpoints 1 and 2 dilutions higher, respectively. The disk diffusion zone diameter correlates were susceptible at ≥28 mm, intermediate at 25 to 27 mm, and resistant at ≤24 mm. Revised lower tetracycline MIC breakpoints were suggested as susceptible at ≤1 μg/ml, intermediate at 2 μg/ml, and resistant at ≥4 μg/ml. Suggested tetracycline disk diffusion zones were identical to those of doxycycline.     

Expression of CXCR3 and its ligands CXCL9, ‐10 and ‐11 in paediatric opsoclonus–myoclonus syndrome

Opsoclonus–myoclonus syndrome (OMS) is a neuroinflammatory disorder associated with remote cancer. To understand more clearly the role of inflammatory mediators, the concentration of CXCR3 ligands CXCL10, CXCL9 and CXCL11 was measured in 245 children with OMS and 81 paediatric controls using enzyme‐linked immunosorbent assay (ELISA), and CXCR3 expression on CD4⁺ T cells was measured by flow cytometry. Mean cerebrospinal fluid (CSF) CXCL10 was 2·7‐fold higher in untreated OMS than controls. Intrathecal production was demonstrated by significantly different CXCL10 CSF : serum ratios. The dichotomized ‘high’ CSF CXCL10 group had higher CSF leucocyte count (P = 0·0007) and B cell activating factor (BAFF) and CXCL13 concentrations (P < 0·0001). CSF CXCL10 did not correlate with clinical severity or relapse using grouped data, although it did in some patients. Among seven types of immunotherapy, including rituximab or chemotherapy, only adrenocorticotrophic hormone (ACTH) monotherapy showed reduced CSF CXCL10, but prospective longitudinal studies of ACTH combination therapies indicated no reduction in CXCL10 despite clinical improvement (P < 0·0001). CXCL10 concentrations were 11‐fold higher in CSF and twofold higher in serum by multiplexed fluorescent bead‐based immunoassay than enzyme‐linked immunosorbent assay, but the two correlated (r = 0·7 and 0·83). In serum, no group differences for CXCL9 or CXCL11 were found. CXCR3 expression on CD4⁺ T cells was fivefold higher in those from CSF than blood, but was not increased in OMS or altered by conventional immunotherapy. These data suggest alternative roles for CXCL10 in OMS. Over‐expression of CXCL10 was not reduced by clinical immunotherapies as a whole, indicating the need for better therapeutic approaches.     

Early inhibition of the renin‐angiotensin system improves the long‐term graft survival of single pediatric donor kidneys transplanted in adult recipients

Transplanting single pediatric donor kidneys into adult recipients has an increased risk of hyperfiltration injury and graft loss. It is unknown if renin‐angiotensin system (RAS) blockers are beneficial in this setting. We retrospectively analyzed 94 adults who received single kidneys from donors <10 years old during 1996–2009. The recipients were divided into group 1 with RAS blockers (n = 40) and group 2 without RAS blockers (n = 54) in the first year of transplant. There was no significant difference in any donor/recipient demographic between the two groups. Graft function, incidence of delayed graft function, acute rejection, and persistent proteinuria were not statistically different either. Kaplan–Meier estimated death‐censored graft survivals were significantly better in group 1 than in group 2: 95 vs. 81.2%, 82.4 vs. 61.2%, 72.6 vs. 58.5%, and 68.5 vs. 47.2% at 1, 3, 5, and 7 years, respectively (log rank P = 0.043). Multivariable analysis found persistent proteinuria was a risk factor for graft loss (OR 2.70, 95% CI 1.33–5.49, P = 0.006), while RAS blockers reduced the risk of graft loss (OR 0.38, 95% CI 0.18–0.79, P = 0.009). Early RAS blockade therapy in the first year of transplant is associated with superior long‐term graft survival among adults transplanted with single pediatric donor kidneys.     

Metachronous T‐Lymphoblastic Lymphoma and Burkitt Lymphoma in a Child With Constitutional Mismatch Repair Deficiency Syndrome

Constitutional mismatch repair deficiency (CMMRD) is a cancer predisposition syndrome associated with a high risk of developing early‐onset malignancies of the blood, brain, and intestinal tract. We present the case of a patient with T‐lymphoblastic lymphoma at the age of 3 years, followed by Burkitt lymphoma 10 years later. This patient also exhibited numerous nonmalignant findings including café au lait spots, lipomas, bilateral renal nodules, a nonossifying fibroma, multiple colonic adenomas, and a rapidly enlarging pilomatrixoma. The spectrum of malignant and nonmalignant neoplasms in this patient highlights the remarkable diversity, and early onset, of lesions seen in children with CMMRD.