Bettina Wabbels

Human TUBB3 Mutations Perturb Microtubule Dynamics, Kinesin Interactions, and Axon Guidance

We report that eight heterozygous missense mutations in TUBB3, encoding the neuron-specific beta-tubulin isotype III, result in a spectrum of human nervous system disorders that we now call the TUBB3 syndromes. Each mutation causes the ocular motility disorder CFEOM3, whereas some also result in intellectual and behavioral impairments, facial paralysis, and/or later-onset axonal sensorimotor polyneuropathy. Neuroimaging reveals a spectrum of abnormalities including hypoplasia of oculomotor nerves and dysgenesis of the corpus callosum, anterior commissure, and corticospinal tracts. A knock-in disease mouse model reveals axon guidance defects without evidence of cortical cell migration abnormalities. We show that the disease-associated mutations can impair tubulin heterodimer formation in vitro, although folded mutant heterodimers can still polymerize into microtubules. Modeling each mutation in yeast tubulin demonstrates that all alter dynamic instability whereas a subset disrupts the interaction of microtubules with kinesin motors. These findings demonstrate that normal TUBB3 is required for axon guidance and maintenance in mammals.

Genotype-phenotype correlation and longitudinal course in ten families with Best vitelliform macular dystrophy

AimLongitudinal course and genotype-phenotype correlation in patients and carriers with heterozygous mutations in hBEST1 (bestrophin).MethodsThirteen patients and seven possible carriers were characterised by mutation analysis with SSCPA and direct sequencing, clinical examination and fundus autofluorescence (AF). Electrophysiology (EOG and mfERG) and optical coherence tomography (OCT) were additionally performed whenever possible.ResultsWe identified seven different heterozygous mutations in ten unrelated families with Best disease. I296del was the most frequent mutation. Five of nine individuals with I295del and two of three with N99K were asymptomatic carriers. One patient with I295del mutation had funduscopically unilateral Best disease. In three children (all with I295del), EOG initially showed a clearly present light peak that deteriorated during 5 years of follow-up in two of them. Increased AF corresponded well to funduscopically visible lesions. During 3–6 years of follow-up, the lesion area did not change significantly, but there were obvious changes in the inner structure of the lesion.ConclusionIn the present series I295del, the most frequent mutation in our study, and N99K showed reduced penetrance. EOG was normal in young patients even if prime signs were visible. The lesion area did not depend on the mutation and did not correlate with VA. Lower VA was associated with a more irregular AF pattern due to scarring or haemorrhage. Our results indicate a disease causing effect that is cumulative over time.

Difficulties with differentiating botulinum toxin treatment effects in essential blepharospasm.

Blepharospasm is a focal dystonia in which the extraocular muscles contract repetitively, leading to excessive blinking and forced eyelid closure. Botulinum toxin type A (BoNTA) is the primary symptomatic treatment for blepharospasm and its effects have been evaluated using numerous rating scales. The main scales in use today were initially used to determine whether BoNTA treatment was superior to placebo, and most controlled trials have confirmed this. More recently, these scales have been used to determine whether there are efficacy differences between different BoNTs in blepharospasm. However, although the scales used in these trials are able to differentiate the effects of BoNT from placebo, they may not be sensitive enough to differentiate between BoNTs. Most of the scales include only four possible points for each item, which would necessitate a 25% greater improvement in one group than the other to detect any differences. Current scales are also relatively insensitive to patients with mild disability who may experience mainly psychosocial problems related to their blepharospasm. Clinical trials comparing BoNTs that include substantial numbers of mildly affected patients may be unlikely to find differences because the scales do not adequately measure mild symptoms. Additional challenges with evaluating blepharospasm include the lack of precision and objectivity of current measures, symptom variability, the need to evaluate aspects of the disorder that are most important to patients, and the different types of blepharospasm. Although no single scale may be able to capture all relevant aspects of blepharospasm, more sensitive and patient-centered scales are needed.

Botulinum toxin in hemifacial spasm: the challenge to assess the effect of treatment

Hemifacial spasm is characterized by intermittent tonic or clonic contractions of the muscles supplied by the facial nerve. Although vision is less impaired than in patients with blepharospasm, the disease can impose significant psychosocial burden on patient’s life. Botulinum toxin (BoNT) is the well-established pharmacotherapy of choice, but evidence from controlled clinical trials is sparse. There is a broad variety of rating scales used in clinical studies with BoNT and obviously no consensus has been reached how to assess treatment outcome in hemifacial spasm. Clinical rating scales focusing on objective function were used in a couple of controlled studies with BoNT and were appropriate to discriminate between BoNTA and placebo. But it has not been shown that they would be sensitive enough to detect minor differences between several BoNT formulations. Although most of the clinical scales consist of a five-point rating, the descriptors for the ordinal numbers are not necessarily the same so that the results of different clinical studies are not comparable to each other. The main disadvantage of clinical scales is that they do not take into account patient’s perspective of disability and impact on daily life. For this reason some clinical studies applied health-related quality of life (HRQoL) questionnaires to assess efficacy, and one research group worked on the development of disease-specific tools. Although these HRQoL questionnaires have been validated and a good correlation to disease severity could be demonstrated, they are far from having become an established variable for efficacy assessment in hemifacial spasm trials. The challenge remains to establish tools which are appropriate to rate BoNT treatment effects in hemifacial spasm. Currently, it is virtually impossible to identify one rating scale which can cover all relevant aspects of the disorder. In consequence we recommend the implementation of a combination of different rating scales which address functional impairment as well as those issues which are most important to patients. Further research is needed to standardize and validate rating scales for hemifacial spasm in clinical studies.

Depression in blepharospasm: a question of facial feedback?

Depression is the most important nonmotor symptom in blepharospasm (BL). As facial expression influences emotional perception, summarized as the facial feedback hypothesis, we investigated if patients report fewer depressive symptoms if injections of botulinum neurotoxin (BoNT) include the “grief muscles” of the glabellar region, compared to treatment of orbicularis oculi muscles alone. Ninety BL patients were included, half of whom had BoNT treatment including the frown lines. While treatment pattern did not predict depressive symptoms overall, subgroup analysis revealed that in male BL patients, BoNT injections into the frown lines were associated with remarkably less depressive symptoms. We hypothesize that in BL patients presenting with dystonia of the eyebrow region, BoNT therapy should include frown line application whenever justified, to optimize nonmotor effects of BoNT denervation.

Botulinum Toxin Therapy in Congenital Blepharospasm

Botulinum toxin injections are the treatment of choice for the management of essential blepharospasm in adults. No cases of congenital blepharospasm have been described in the literature so far, and no cases of botulinum toxin injection in an infant have been reported. A 4-week-old girl was referred to our department with absent eye opening and spasmodically closed eyes. Pregnancy and delivery had been normal. A neuropediatric examination did not reveal useful findings. A periorbital injection of botulinum toxin was performed at the age of 2 months to prevent deprivation amblyopia. Four days later, clearly visible bilateral eye opening and commencement of eye contact were observed. At the age of 3 years, her eyelids remain open and no side effects of botulinum toxin therapy have occurred.