Heather M. Johnston

The expanding phenotype of laminin alpha2 chain (merosin) abnormalities: case series and review.

Initial reports of patients with laminin α2 chain (merosin) deficiency had a relatively homogeneous phenotype, with classical congenital muscular dystrophy (CMD) characterised by severe muscle weakness, inability to achieve independent ambulation, markedly raised creatine kinase, and characteristic white matter hypodensity on cerebral magnetic resonance imaging. We report a series of five patients with laminin α2 deficiency, only one of whom has this severe classical CMD phenotype, and review published reports to characterise the expanded phenotype of laminin α2 deficiency, as illustrated by this case series. While classical congenital muscular dystrophy with white matter abnormality is the commonest phenotype associated with laminin α2 deficiency, 12% of reported cases have later onset, slowly progressive weakness more accurately designated limb-girdle muscular dystrophy. In addition, the following clinical features are reported with increased frequency: mental retardation (∼6%), seizures (∼8%), subclinical cardiac involvement (3-35%), and neuronal migration defects (4%). At least 25% of patients achieve independent ambulation. Notably, three patients with laminin α2 deficiency were asymptomatic, 10 patients had normal MRI (four withLAMA2 mutations reported), and between 10-20% of cases had maximum recorded creatine kinase of less than 1000 U/l. LAMA2 mutations have been identified in 25% of cases. Sixty eight percent of these have the classical congenital muscular dystrophy, but this figure is likely to be affected by ascertainment bias. We conclude that all dystrophic muscle biopsies, regardless of clinical phenotype, should be studied with antibodies to laminin α2. In addition, the use of multiple antibodies to different regions of laminin α2 may increase the diagnostic yield and provide some correlation with severity of clinical phenotype.

Dystrophin gene mutation location and the risk of cognitive impairment in Duchenne muscular dystrophy.

Background A significant component of the variation in cognitive disability that is observed in Duchenne muscular dystrophy (DMD) is known to be under genetic regulation. In this study we report correlations between standardised measures of intelligence and mutational class, mutation size, mutation location and the involvement of dystrophin isoforms. Methods and Results Sixty two male subjects were recruited as part of a study of the cognitive spectrum in boys with DMD conducted at the Sydney Childrens Hospital (SCH). All 62 children received neuropsychological testing from a single clinical psychologist and had a defined dystrophin gene (DMD) mutation; including DMD gene deletions, duplications and DNA point mutations. Full Scale Intelligence Quotients (FSIQ) in unrelated subjects with the same mutation were found to be highly correlated (r = 0.83, p = 0.0008), in contrast to results in previous publications. In 58 cases (94%) it was possible to definitively assign a mutation as affecting one or more dystrophin isoforms. A strong association between the risk of cognitive disability and the involvement of groups of DMD isoforms was found. In particular, improvements in the correlation of FSIQ with mutation location were identified when a new classification system for mutations affecting the Dp140 isoform was implemented. Significance These data represent one of the largest studies of FSIQ and mutational data in DMD patients and is among the first to report on a DMD cohort which has had both comprehensive mutational analysis and FSIQ testing through a single referral centre. The correlation between FSIQ results with the location of the dystrophin gene mutation suggests that the risk of cognitive deficit is a result of the cumulative loss of central nervous system (CNS) expressed dystrophin isoforms, and that correct classification of isoform involvement results in improved estimates of risk.

Postoperative Chemotherapy in Children Less Than 4 Years of Age with Malignant Brain Tumors: Promising Initial Response to a Vetopec-based Regimen A Study of the Australian and New Zealand Children's Cancer Study Group (anzccsg)

Purpose: Postoperative chemotherapy with indefinite postponement of radiation therapy in children <4 years old with brain tumors was investigated in a multi-institutional study. Patients and Methods: From 1991 to 1995. 42 patients aged 3 to 47 months (median 20) with brain tumors were enrolled in a 2-phase chemotherapy protocol: 16 patients had medulloblastoma (MB); 8 had supratentorial primitive neuroectodermal tumor (PNET); 14 had ependymoma; and 4 had other tumors. The initial phase was comprised of 4 courses of the 3-drug regimen: vineristine (VCR), etoposide (VP-16). and intensive cyclophosphamide (CPA) in a previously reported schedule (VFTOPEC). The continuation phase was comprised of 2-drug courses: A. CPA + VCR: B. cisplatin + VP-16; and C. carbopfatin + VP-16, for a total duration of 64 weeks. Results: Response to VETOPFC was evaluable in 28 patients with postresection residual (25) and/or metastatic (1 M2, 6 M3) tumor. There were 9 complete responses (CR) and 9 partial responses (PR) with a combined CR + PR of 64% (95% confidence interval [CI] 44 to 81). In 12 evaluable patients with MB, CR + PR was 82% (48 to 98); in 6 patients with PNET. 50% (12 to 88); and, in 8 patients with ependymoma. 86% (42 to 99). Of 40 patients eligible for further analysis, 6 remain progressionfree at a median of 30 months, 14 are alive at a median of 38 months. 29 have progressed at a median of 7 months (range. 2 to 37 months), and 26 have died. The progression-free and overall survival rates at 36 months are estimated to be 11% (95% CI 1 to 22) and 34% (18 to 50). respectively. Conclusions: The initial response to the VETOPEC regimen is encouraging and warrants study of further dose escalation. Survival remains poor with current strategies in this high-risk population.

Pathophysiological insights derived by natural history and motor function of spinal muscular atrophy.

OBJECTIVE To examine the natural history of spinal muscular atrophy (SMA) to gain further insight into the clinical course and pathogenesis. STUDY DESIGN Survival pattern, age of onset, and ambulatory status were retrospectively analyzed in 70 patients with SMA with deletions of the survival motor neuron 1 genes that presented to a specialized neuromuscular clinic. The Kaplan-Meier method was used to obtain survival curves. Hammersmith Functional Motor Scale-Expanded and abductor pollicis brevis compound muscle action potential amplitudes were assessed in 25 of the surviving cohort and correlated with survival motor neuron 2 copy number. RESULTS Survival probabilities at ages 1, 2, 4, 10, 20, and 40 years were 40%, 25%, 6%, and 0%, respectively, for patients with SMA type 1; 100%, 100%, 97%, 93%, 93%, and 52% for patients with SMA type 2 and all patients with SMA type 3 were alive (age range 7-33 years). There were significant associations between age of onset and long-term outcome, specifically survival in SMA type 1 (P < .01) and Hammersmith Functional Motor Scale-Expanded (P < .0001), and compound muscle action potential (P = .001) in SMA types 2 and 3. Motor function in patients with long-standing SMA reduced over prolonged periods or remained stable. Survival motor neuron 2 copy number related to continuing changes in motor function with age. CONCLUSION The natural history of SMA suggests considerable early loss of motor neurons, with severity related to differences in the number of remaining motor neurons. As the ensuing chronic course in milder phenotypes suggests relative stability of remaining motor neurons, the maximal therapeutic window presents early.

Postoperative chemotherapy without radiation in young children with malignant non-astrocytic brain tumours. A report from the Australia and New Zealand Childhood Cancer Study Group (ANZCCSG).

Young children with malignant brain tumours have particularly poor survival and manifest severe sequelae of radiation therapy. A multi-institutional pilot study of post-operative primary chemotherapy for children under 3 years with primitive neuroectodermal tumours (PNET) or ependymoma was initiated in 1987. The chemotherapy protocol comprised earboplatin, vincristine and the “eight drugs in 1 day” regimen. Radiation was recommended only if tumour progression or recurrence was documented. A total of 14 patients between 5 and 36 months of age were enrolled. Seven had supratentorial tumours (PNET, pinealoblastoma, intracranial retinoblastoma) with multiple predictors of adverse outcome. Four of these responded to initial chemotherapy but subsequently progressed and all had died by 16 months from diagnosis. The seven patients with infratentorial tumours (three medulloblastomas, four ependymomas) had more favourable predictors of outcome: no meningeal dissemination and gross macroscopic resection in six of the seven cases. One patient progressed rapidly and died within 5 months. The other six are alive at 37–57 months from diagnosis. Four are in continuous complete remission at 57, 51, 41 and 37 months, respectively from the time of their tumour resection. One is described as having stable disease with a persistent radiographic lesion at 41 months from diagnosis. One has relapsed on two occasions and is the only surviving patient to have been irradiated. Intelligence scores for the six long-term survivors have thus for remained within the normal range. It is suggested that some infants with standard-risk ependymoma and, possibly, medulloblastoma may be cured without radiation therapy.

Intracranial Tumors in Infants

The prognosis in infants with brain tumors has historically been very poor. This study reviews 16 infants under the age of 12 months with brain tumors who presented to our institution between 1988 and 1999. The aim was to describe the clinical presentation, diagnosis, and management of these patients and to establish if newer diagnostic and treatment modalities have improved prognosis in terms of survival and neurocognitive outcome. Charts were reviewed retrospectively for age at diagnosis, time to diagnosis, presenting features, location, histology, surgical and adjuvant treatment, survival, and neurocognitive outcome. Survival has improved. Three quarters of the patients remain alive. The 5-year survival rate was 81%. The 5-year progression-free survival rate was 51%, with a median follow-up time of 70 months. The 5-year survival rate for benign tumors was 100%. None of the children with malignant tumors survived. Morbidity remains high: 8 of 13 survivors had focal neurologic deficits, 7 of 13 had epilepsy, and 7 of 12 had significant cognitive disability. Future treatment protocols should include formal analysis of neurocognitive morbidity, functional outcome, and quality of life measures to provide accurate prognostic information and to prepare families for early intervention programs. (J Child Neurol 2004; 19:424-430).

Measurement of the clinical utility of a combined mutation detection protocol in carriers of Duchenne and Becker muscular dystrophy

Background: Recent methodological advances have improved the detection rate for dystrophin mutations, but there are no published studies that have measured the clinical utility of these protocols for carrier detection compared with conventional carrier testing protocols that use pedigree, serum creatine kinase levels and linkage analysis. Methods and subjects: The clinical utility of a combined mutation detection protocol was measured. It involved quantitative PCR procedures followed by DNA sequence analysis for the identification of dystrophin mutation carriers in 2101 women at risk of being carriers from 348 mutation-known Duchenne or Becker muscular dystrophy pedigrees. Results: The combined mutation detection protocol identified a mutation in 96% and 82% of index cases of Duchenne muscular dystrophy and Becker muscular dystrophy, respectively. An additional 692 (33%) potential carriers were correctly classified by the combined mutation detection protocol compared with pedigree, serum creatine kinase levels and linkage analysis. Significantly lower mutation carrier rates were identified in the mothers of isolated cases with deletion mutations than predicted from theoretical considerations, but these findings were not confirmed for duplication and DNA sequence mutations. Conclusions: There are significant clinical benefits to be gained from a combined mutation detection protocol for carrier detection. It is recommended that mutation-specific carrier frequencies for the different classes of dystrophin mutations should be taken into account in genetic counselling practice.

Importance and challenge of making an early diagnosis in LMNA-related muscular dystrophy

Objective: To identify the most useful clinical and histologic markers that facilitate early diagnosis in LMNA-related muscular dystrophy and to assess the usefulness of Western blotting (WB) for lamin A/C. Methods: We analyzed the clinical and histologic features and WB results of all patients with laminopathies diagnosed in a research-based diagnostic service over 8 years. Results: Although patients with congenital muscular dystrophy (MDCL) (n = 5) and Emery-Dreifuss muscular dystrophy (EDMD) (n = 5) had distinctive early clinical features, the lack of a suggestive clinical phenotype significantly delayed diagnosis in 2 of 3 patients with limb-girdle muscular dystrophy (LGMD) (n = 3). In addition, 6 of 20 muscle biopsy samples were considered nondystrophic, which contributed to delays in diagnosis in some patients. Neck extensor involvement (weakness or contractures) was the most consistent clinical sign, present in all patients. Reduced lamin A/C levels on WB were seen in 5 of 9 patients with laminopathies. Conclusion: Clinical features provide the best clues for diagnosing MDCL and EDMD early in the disease, and we urge clinicians to become familiar with those phenotypes. WB for lamin A/C may contribute to diagnosis but requires technical expertise, and results are normal in many individuals with LMNA mutations. Because of the survival benefit of early diagnosis and treatment, we recommend that LMNA gene sequencing be performed in all patients with undiagnosed congenital muscular dystrophy and neck extensor weakness, all patients with genetically undiagnosed LGMD, and those with suggestive clinical signs and nonspecific histologic abnormalities.

Dysfunction of axonal membrane conductances in adolescents and young adults with spinal muscular atrophy

Spinal muscular atrophy is distinct among neurodegenerative conditions of the motor neuron, with onset in developing and maturing patients. Furthermore, the rate of degeneration appears to slow over time, at least in the milder forms. To investigate disease pathophysiology and potential adaptations, the present study utilized axonal excitability studies to provide insights into axonal biophysical properties and explored correlation with clinical severity. Multiple excitability indices (stimulus–response curve, strength–duration time constant, threshold electrotonus, current–threshold relationship and recovery cycle) were investigated in 25 genetically characterized adolescent and adult patients with spinal muscular atrophy, stimulating the median motor nerve at the wrist. Results were compared with 50 age-matched controls. The Medical Research Council sum score and Spinal Muscular Atrophy Functional Rating Scale were used to define the strength and motor functional status of patients with spinal muscular atrophy. In patients with spinal muscular atrophy, there were reductions in compound muscle action potential amplitude (P < 0.0005) associated with reduction in stimulus response slope (P < 0.0005), confirming significant axonal loss. In the patients with mild or ambulatory spinal muscular atrophy, there was reduction of peak amplitude without alteration in axonal excitability; in contrast, in the non-ambulatory or severe spinal muscular atrophy cohort prominent changes in axonal function were apparent. Specifically, there were steep changes in the early phase of hyperpolarization in threshold electrotonus (P < 0.0005) that correlated with clinical severity. Additionally, there were greater changes in depolarizing threshold electrotonus (P < 0.0005) and prolongation of the strength-duration time constant (P = 0.001). Mathematical modelling of the excitability changes obtained in patients with severe spinal muscular atrophy supported a mixed pathology comprising features of axonal degeneration and regeneration. The present study has provided novel insight into the pathophysiology of spinal muscular atrophy, with identification of functional abnormalities involving axonal K+ and Na+ conductances and alterations in passive membrane properties, the latter linked to the process of neurodegeneration.

Spinal Muscular Atrophy: Molecular Mechanisms

Spinal muscular atrophy (SMA) is a relatively common autosomal recessive neuromuscular disorder characterised by muscle weakness and atrophy due to degeneration of motor neurons of the spinal cord and cranial motor nuclei. The clinical phenotype incorporates a wide spectrum. No effective treatment is currently available and patients may experience severe physical disability which is often life limiting. The most common type of SMA is caused by homozygous disruption of the survival motor neuron 1 (SMN1) gene by deletion, conversion or mutation and results in insufficient levels of survival motor neuron (SMN) protein in motor neurons. While diagnosis is usually achieved by genetic testing, an illustrative clinical case is described that highlights the molecular and diagnostic complexities. While there is an emerging picture concerning the function of the SMN protein and the molecular pathophysiological mechanisms underpinning the disease, a number of substantial issues remain unresolved. The selective vulnerability of the motor neuron and the site and timing of the primary pathogenesis are not yet determined. Utilising the organisation of the SMN genomic region, recent advances have identified a number of potential therapeutic targets. As such, this review incorporates discussion of the clinical manifestations, molecular genetics, diagnosis, mechanisms of disease pathogenesis and development of novel treatment strategies.