Novel truncating variant in KMT2E associated with cerebellar hypoplasia and velopharyngeal dysfunction

KMT2E‐related neurodevelopmental disorder is a recently described intellectual disability syndrome often with speech difficulties. Here, we describe an individual with a heterozygous frameshift variant in KMT2E (NM_182931.2:c.2334_2337delTTAC, p.[Tyr779AlafsTer41]), intellectual disability, cerebellar hypoplasia, and velopharyngeal dysfunction. This case suggests potential mechanisms of speech disturbance in the disorder, requiring further investigation.

Longitudinal MRI brain volume changes over one year in children with mucopolysaccharidosis types IIIA and IIIB

OBJECTIVE

To quantify changes in segmented brain volumes over 12 months in children with mucopolysaccharidosis types IIIA and IIIB (MPS IIIA and IIIB).

METHODS

In order to establish suitable outcome measures for clinical trials, twenty-five children greater than 2 years of age were enrolled in a prospective natural history study of MPS IIIA and IIIB at Nationwide Children's Hospital. Data from sedated non-contrast brain 3 T MRIs and neuropsychological measures were reviewed from the baseline visit and at 12-month follow-up. No intervention beyond standard clinical care was provided. Age- and sex-matched controls were gathered from the National Institute of Mental Health Data Archive. Automated brain volume segmentation with longitudinal processing was performed using FreeSurfer.

RESULTS

Of the 25 subjects enrolled with MPS III, 17 children (4 females, 13 males) completed at least one MRI with interpretable volumetric data. The ages ranged from 2.8 to 13.7 years old (average 7.2 years old) at enrollment, including 8 with MPS IIIA and 9 with MPS IIIB. At baseline, individuals with MPS III demonstrated reduced cerebral white matter and corpus callosum volumes, but greater volumes of the lateral ventricles, cerebellar cortex, and cerebellar white matter compared to controls. Among the 13 individuals with MPS III with two interpretable MRIs, there were annualized losses or plateaus in supratentorial brain tissue volumes (cerebral cortex -42.10 ± 18.52 cm³/year [mean ± SD], cerebral white matter -4.37 ± 11.82 cm³/year, subcortical gray matter -6.54 ± 3.63 cm³/year, corpus callosum -0.18 ± 0.62 cm³/yr) and in cerebellar cortex (-0.49 ± 12.57 cm³/year), with a compensatory increase in lateral ventricular volume (7.17 ± 6.79 cm³/year). Reductions in the cerebral cortex and subcortical gray matter were more striking in individuals younger than 8 years of age. Greater cerebral cortex volume was associated with higher fine and gross motor functioning on the Mullen Scales of Early Learning, while greater subcortical gray matter volume was associated with higher nonverbal functioning on the Leiter International Performance Scale. Larger cerebellar cortex was associated with higher receptive language performance on the Mullen, but greater cerebellar white matter correlated with worse adaptive functioning on the Vineland Adaptive Behavioral Scales and visual problem-solving on the Mullen.

CONCLUSIONS

Loss or plateauing of supratentorial brain tissue volumes may serve as longitudinal biomarkers of MPS III age-related disease progression compared to age-related growth in typically developing controls. Abnormally increased cerebellar white matter in MPS III, and its association with worse performance on neuropsychological measures, suggest the possibility of pathophysiological mechanisms distinct from neurodegeneration-associated atrophy that warrant further investigation.

Moyamoya syndrome in a child with Legius syndrome: Introducing a cerebral vasculopathy to the SPRED1 phenotype?

Legius syndrome is a disorder of the RAS and mitogen-activated protein kinase (MAPK) pathway first described in 2007 by Eric Legius, et al., that has been considered a milder phenotype than reported in the RASopathy neurofibromatosis type 1 (NF1). However, with approximately 200 cases reported in the literature, the Legius syndrome phenotype remains to be fully characterized. We report a child who presented with moyamoya syndrome and who has Legius syndrome due to a pathogenic variant in SPRED1. Vascular complications such as moyamoya syndrome have been reported in NF1. However, this association has not been reported in Legius syndrome. This child's case may represent an expansion of the clinical phenotype of Legius syndrome, and further study is needed. We emphasize the importance of obtaining neuroimaging studies in patients with Legius syndrome who present with new neurologic deficits.

Expanding the spectrum of CEP55-associated disease to viable phenotypes

Homozygosity for nonsense variants in CEP55 has been associated with a lethal condition characterized by multinucleated neurons, anhydramnios, renal dysplasia, cerebellar hypoplasia, and hydranencephaly (MARCH syndrome) also known as Meckel-like syndrome. Missense variants in CEP55 have not previously been reported in association with disease. Here we describe seven living individuals from five families with biallelic CEP55 variants. Four unrelated individuals with microcephaly, speech delays, and bilateral toe syndactyly all have a common CEP55 variant c.70G>A p.(Glu24Lys) in trans with nonsense variants. Three siblings are homozygous for a consensus splice site variant near the end of the gene. These affected girls all have severely delayed development, microcephaly, and varying degrees of lissencephaly/pachygyria. Here we compare our seven patients with three previously reported families with a prenatal lethal phenotype (MARCH syndrome/Meckel-like syndrome) due to homozygous CEP55 nonsense variants. Our series suggests that individuals with compound heterozygosity for nonsense and missense variants in CEP55 have a different viable phenotype. We show that homozygosity for a splice variant near the end of the CEP55 gene is also compatible with life.

Evaluation of biomarkers for Sanfilippo syndrome

Sanfilippo syndrome or mucopolysaccharidosis type III (MPS III) is a childhood metabolic disorder marked by neuropathology arising due to impaired heparan sulphate (HS) catabolism. Consequently, partially degraded HS accumulates in the lysosomes of affected cells and is excreted in the urine. The measurement of HS in urine has long been considered a biomarker of Sanfilippo syndrome although it is largely non-specific. Using blood, urine and CSF collected from a cohort of Sanfilippo patients we investigated the utility of primary and secondary biomarkers to inform on disease activity. These included enzyme activity, specific oligosaccharides with non-reducing end residues reflective of the enzyme deficiency, and gangliosides. The diagnostic oligosaccharides - a HS disaccharide and tetrasaccharide - were elevated in the urine, plasma and CSF of all MPS IIIA and IIIB patients, respectively. There was no correlation between the concentrations in any of the matrices suggesting they reflect specific tissues and not overall disease burden. Enzyme activity did not inform on disease severity, with no measurable activity in CSF and activity approaching normal in MPS IIIA plasma. The concentration of gangliosides, G_M2 and G_M3, were significantly higher in the CSF of all MPS III subjects when compared to controls and correlated with the age of onset of first symptoms. Given that these gangliosides reflect delayed brain development they may be useful measures of disease burden, within the limitations of the clinical surrogates. Observation of these biochemical measurements in MPS III patients enrolled in clinical trials may determine whether they represent true pharmacodynamics biomarkers.

Natural history of echocardiographic abnormalities in mucopolysaccharidosis III

BACKGROUND

Mucopolysaccharidosis (MPS) type III, Sanfilippo Syndrome, is an autosomal recessive lysosomal storage disorder. MPS I and II patients often develop cardiac involvement leading to early mortality, however there are limited data in MPS III. The objective of this study is to describe cardiac abnormalities in a large group of MPS III patients followed in a longitudinal natural history study designed to determine outcome measures for gene transfer trials.

METHODS

A single center study of MPS III patients who were enrolled in the Nationwide Children's Hospital natural history study in 2014. Two cardiologists reviewed all patient echocardiograms for anatomic, valvular, and functional abnormalities. Valve abnormalities were defined as abnormal morphology, trivial mitral regurgitation (MR) with abnormal morphology or at least mild MR, and any aortic regurgitation (AR). Abnormal left ventricular (LV) function was defined as ejection fraction < 50%. Group comparisons were assessed using two-sample t-tests or Wilcoxon rank sum tests for continuous variables and chi-square or Fisher's exact tests for categorical variables.

RESULTS

Twenty-five patients, 15 Type A and 10 Type B MPS III, underwent 45 echocardiograms. Fifteen patients (60%) demonstrated an abnormal echocardiographic finding with age at first abnormal echocardiogram within the study being 6.8 ± 2.8 years. Left-sided valve abnormalities were common over time: 7 mitral valve thickening, 2 mitral valve prolapse, 16 MR (8 mild, 8 trivial), 3 aortic valve thickening, and 9 AR (7 mild, 2 trivial). Two patients had asymmetric LV septal hypertrophy. No valvular stenosis or ventricular function abnormalities were noted. Incidental findings included: mild aortic root dilation (2), bicommissural aortic valve (1), and mild tricuspid regurgitation (3).

CONCLUSIONS

Individuals with Sanfilippo A and B demonstrate a natural history of cardiac involvement with valvular abnormalities most common. In short-term follow up, patients demonstrated only mild progression of abnormalities, none requiring intervention. Valvular disease prevalence is similar to MPS I and II, but appears less severe. These findings raise no specific concerns for gene transfer trials in patients in this age range.

Differential Prevalence of Antibodies Against Adeno-Associated Virus in Healthy Children and Patients with Mucopolysaccharidosis III: Perspective for AAV-Mediated Gene Therapy

Recombinant adeno-associated virus (AAV) vectors are promising gene therapy tools. However, pre-existing antibodies (Abs) to many useful AAV serotypes pose a critical challenge for the translation of gene therapies. As part of AAV gene therapy program for treating mucopolysaccharidosis (MPS) III patients, the seroprevalence profiles of AAV1-9 and rh74 were investigated in MPS IIIA/IIIB patients and in healthy children. Using enzyme-linked immunosorbent assay for αAAV-IgG, significantly higher seroprevalence was observed for AAV1 and AAVrh74 in 2- to 7-year-old MPS III patients than in healthy controls. Seroprevalence for the majority of tested AAV serotypes appears to peak before 8 years of age in MPS III subjects, with the exception of increases in αAAV8 and αAAV9 Abs in 8- to 19-year-old MPS IIIA patients. In contrast, significant increases in seroprevalence were observed for virtually all tested AAV serotypes in 8- to 15-year-old healthy children compared to 2- to 7-year-olds. Co-prevalence and Ab level correlation results followed the previously established divergence-based clade positions of AAV1-9. Interestingly, the individuals positive for αAAVrh74-Abs showed the lowest co-prevalence with Abs for AAV1-9 (22-40%). However, all or nearly all (77-100%) of subjects who were seropositive for any of serotypes 1-9 were also positive for αAAVrh74-IgG. Notably, the majority (78%) of αAAV seropositive individuals were also Ab-positive for one to five of the tested AAV serotypes, mostly with low levels of αAAV-Abs (1:50-100), while a minority (22%) were seropositive for six or more AAV serotypes, mostly with high levels of αAAV-IgG for multiple serotypes. In general, the highest IgG levels were reactive to AAV2, AAV3, and AAVrh74. The data illustrate the complex seroprevalence profiles of AAV1-9 and rh74 in MPS patients and healthy children, indicating the potential association of AAV seroprevalence with age and disease conditions. The broad co-prevalence of Abs for different AAV serotypes reinforces the challenge of pre-existing αAAV-Abs for translating AAV gene therapy to clinical applications, regardless of the vector serotype.

General anesthesia with a native airway for patients with mucopolysaccharidosis type III

BACKGROUND

Mucopolysaccharidosis type III is a progressive disease with worsening airway, pulmonary, and cardiac involvement that may complicate anesthetic care.

AIM

To prospectively evaluate the incidence of airway issues and complications during magnetic resonance imaging (MRI) and lumbar puncture (LP) during general anesthesia with a native airway for patients with mucopolysaccharidosis type III.

METHOD

The study was a part of the natural history study. Anesthesia was induced with sevoflurane, which was discontinued after intravenous access was obtained. General anesthesia with a native airway was provided by dexmedetomidine and propofol. Dexmedetomidine (0.5 μg·kg^-1 ) was administered over 5 min followed by a continuous infusion at 0.5 μg·kg^-1 ·h^-1 . A continuous infusion of propofol was started at 150 μg·kg^-1 ·min^-1 . A bolus dose of propofol (1 mg·kg^-1 ) was administered and the propofol infusion was increased as needed. Airway management and vital signs were recorded for the entire procedure until discharge.

RESULTS

Twenty-five patients (6.9 ± 3.1 years) received total of 43 MRI and LP procedures in the cohort. No patient failed sedation. Although mask induction with sevoflurane was not clinically problematic, upper airway obstruction was noted during 14 procedures (33%). This required the application of continuous positive airway pressure, temporary oral airway placement, jaw thrust, or shoulder roll. Airway dynamics improved once the anesthesia was transitioned to intravenous anesthetic agents. Although a small shoulder roll was needed to improve airway patency for 11 cases (26%), a large shoulder roll tended to make the upper airway obstruction worse. Oxygen desaturation (≤90%) was noted during MRI in three cases (7%).

CONCLUSION

A combination of dexmedetomidine and propofol provided effective general anesthesia with a native airway during the procedures. Although upper airway obstruction was noted, it resolved with simple airway maneuvers without further airway intervention.

A prospective one-year natural history study of mucopolysaccharidosis types IIIA and IIIB: Implications for clinical trial design

Mucopolysaccharidosis type III is a group of four autosomal recessive enzyme deficiencies leading to tissue accumulation of heparan sulfate. Central nervous system disease is prominent, with initial normal development followed by neurocognitive decline leading to death. In order to define outcome measures suitable for gene transfer trials, we prospectively assessed disease progression in MPS IIIA and IIIB subjects >2years old at three time points over one year (baseline, 6 and 12months). Fifteen IIIA (9 male, 6 female; age 5.0±1.9years) and ten IIIB subjects (8 male, 2 female; age 8.6±3years) were enrolled, and twenty subjects completed assessments at all time points. Cognitive function as assessed by Mullen Scales maximized at the 2.5 to 3year old developmental level, and showed a significant age-related decline over a 6month interval in three of five subdomains. Leiter nonverbal IQ (NVIQ) standard scores declined toward the test floor in the cohort by 6 to 8years of age, but showed significant mean declines over a 6month interval in those <7years old (p=0.0029) and in those with NVIQ score≥45 (p=0.0313). Parental report of adaptive behavior as assessed by the Vineland-II composite score inversely correlated with age and showed a significant mean decline over 6month intervals (p=0.0004). Abdominal MRI demonstrated increased volumes in liver (mean 2.2 times normal) and spleen (mean 1.9 times normal) without significant change over one year; brain MRI showed ventriculomegaly and loss of cortical volume in all subjects. Biochemical measures included urine glycosaminoglycan (GAG) levels, which although elevated showed a decline correlating with age (p<0.0001) and approached normal values in older subjects. CSF protein levels were elevated in 32% at enrollment, and elevations of AST and ALT were frequent. CSF enzyme activity levels for either SGSH (in MPS IIIA subjects) or NAGLU (in MPS IIIB) significantly differed from normal controls. Several other behavioral or functional measures were found to be uninformative in this population, including timed functional motor tests. Our results suggest that cognitive development as assessed by the Mullen and Leiter-R and adaptive behavior assessment by the Vineland parent interview are suitable functional outcomes for interventional trials in MPS IIIA or IIIB, and that CSF enzyme assay may be a useful biomarker to assess central nervous system transgene expression in gene transfer trials.