Genetics of laminin alpha 2 chain (or merosin) deficient congenital muscular dystrophy: from identification of mutations to prenatal diagnosis

Congenital muscular dystrophies (CMD) are a clinically and genetically heterogeneous group of muscle disorders, with autosomal recessive inheritance. Absence of the laminin alpha 2 chain in the skeletal muscle of patients with classical CMD has permitted the identification of a subgroup, referred to as 'merosin-deficient CMD or laminin alpha 2 chain deficient CMD'. We first identified a nonsense and a splice site mutation in laminin alpha 2 gene (LAMA2) (Glu1241 stop, 4573-2A-->T). We report here new mutations: nonsense mutations (Glu210stop, Trp2316stop) and 1- and 2-bp deletions (2418 delta C, 6968 delta TA), which result in truncation of the protein either in the short arm domains or in the C terminal globular domain and complete merosin deficiency. Another subgroup, referred to as 'partially-deficient in laminin alpha 2 chain' has been identified recently, and a LAMA2 missense mutation (Cys996Arg) has been shown to cause this partial deficiency. The laminin alpha 2 chain, together with the beta 1 or beta 2 and gamma 1 chains forms either laminin-2 (alpha 2-beta 1-gamma 1) or laminin-4 (alpha 2-beta 2-gamma 1). The LAMA2 mutations induce the formation of abnormal laminins which probably dramatically disturb the assembly and stability of the laminin network, one of the major components of the extracellular matrix in skeletal muscle. We report also the first prenatal diagnosis performed by direct mutation analysis.

Thoracoabdominal pattern of breathing in neuromuscular disorders

STUDY OBJECTIVE

To assess abnormalities in thoracoabdominal pattern of breathing (TAPB) in neuromuscular disorders during spontaneous breathing, intermittent positive pressure ventilation (IPPV) with and without abdominal (AB) binder, and immediately after IPPV.

DESIGN

Repeated measures design: Pre-IPPV spontaneous breathing, IPPV, IPPV with AB binder, and post-IPPV spontaneous breathing. In protocol 1, ventilator pressure was held constant at the individual value habitually adopted in sessions of IPPV. In protocol 2, it was increased stepwise from 5 to 30 cm H2O.

SETTING

University hospital, Department of Pediatrics, Intensive Care, and Neuro-Ventilatory Rehabilitation.

PATIENTS

Thirty-one patients with spinal muscular atrophy (SMA) and 19 patients with myopathy, mean age (+/- SD) 9.7 +/- 3 years.

MEASUREMENTS

Tidal volume (VT), percent thoracic contribution to VT (%RC), the phase angle between the thoracic and the AB volume changes and the labored breathing index, which is an index of asynchrony taking into account both the phase relationships and relative volumes of rib cage and AB compartments.

RESULTS

We observed marked abnormalities in TAPB during spontaneous breathing, especially in the SMA group. %RC, labored breathing index, and phase angle displayed nearly normal values during IPPV. IPPV pressures of 25 to 30 cm H2O were necessary to increase %RC above 80%. AB binding decreased VT, but led to larger thoracic volumes, especially in patients with SMA. Thoracic contribution to VT and thoracic volume after IPPV were higher than baseline levels.

CONCLUSIONS

The quantitative assessment of TAPB enhances the ability to estimate pulmonary function in neuromuscular disorders, and the efficiency of mechanical ventilation.

[Congenital muscular dystrophy with merosin deficiency: clinical, histopathological, immunocytochemical and genetic analysis]

A selective deficiency of a specific laminin isovariant, merosin made of M, B1 and B2 chains, was found in a series of 17 patients affected with congenital muscular dystrophy (CMD). The merosin deficiency was complete in 15 cases, and almost complete in two cases. An overexpression of the laminin A chain was seen in these biopsies, while B1 and B2 chains were normally expressed. Comparison of the clinical data with a series of 18 "merosin-non deficient" cases showed that the "merosin-deficient" cases were forming a more homogenous group than the "non-deficient" one. Hypotonia, contractures, motor development delay were generally more severe in the "merosin-deficient" series of cases. Moreover, white matter alterations were seen in most cases explored by MRI or scan imaging. A genetic linkage with a 6q2 locus, corresponding to the M chain gene localization, was found in a panel of informative families from French and Turkish origin with "merosin deficient" CMD. "Merosin non-deficient" families did not map on this locus. So, the "merosin-deficient" CMD can be considered as a peculiar entity within the group of Congenital Muscular Dystrophies.

Autopsies of sudden infant death syndrome--classification and epidemiology

An enquiry into sudden infant death syndrome (SIDS) in 1987 furnished us with detailed epidemiological data for 281 cases that underwent a thorough post-mortem examination. This analysis uses these data to evaluate the role the autopsy plays in explaining sudden death. The cases were classified into three diagnostic groups: explained causes of death (group 1), unexplained deaths with anomalies (group 2), and no anomaly (group 3). These 281 cases show the three essential features that characterize SIDS: over-representation of males, increased deaths during the second and third months of life, and increased deaths during winter. The autopsy examination revealed that many of these deaths had a medical explanation. Almost half were assigned to group 1. At the time of autopsy, no precise pathology could be diagnosed for 147 deaths; of these, 140 showed histological anomalies. There were only seven sudden deaths for which no abnormal sign was evident at the autopsy. These results are compared with those of similar studies and discussed in connection with three factors: the initial selection of cases, the nature and degree of the investigations, and the possible interpretations of the symptoms uncovered.

Readjusting the localization of merosin (laminin alpha 2-chain) deficient congenital muscular dystrophy locus on chromosome 6q2

The laminin alpha 2-chain gene mutations (LAMA2) are responsible for about 50% of the cases of classical congenital muscular dystrophy. These patients form a clinically homogenous group presenting merosin (laminin alpha 2-chain) deficiency in muscle biopsies. The LAMA2 gene has been previously localized on 6q22-23 and the disease locus mapped in a 16 cM interval in 6q2 by homozygosity mapping. In the present report we establish, by haplotyping additional microsatellites markers in 18 consanguineous families, that LAMA2 gene is more centromeric than previously thought: between the flanking markers, D6S407 and D6S1705, distant of 3 cM. In this interval the microsatellite D6S1620 is homozygous for all the patients. The localization of LAMA2 gene was confirmed by radiation hybrid mapping. The 3 new highly informative markers can be very useful for prenatal diagnosis.

Diaphragmatic paralysis in children: a review of 11 cases

We reviewed 11 pediatric cases of diaphragmatic paralysis related to nonspinal-cord injury which were managed in our Intensive Care Unit over the past 10 years. Three cases were secondary to birth trauma, 7 followed surgical procedures for congenital heart disease, and 1 occurred in association with injuries sustained in a motor vehicle accident. The paralysis was bilateral in 8 children. The diagnosis was initially suspected on clinical grounds because of respiratory distress, impossibility of weaning from the ventilator, and paradoxical abdominal respiratory movements. Confirmatory investigations included chest radiography, which revealed elevation of the affected hemidiaphragm, fluoroscopy and ultrasound, both of which demonstrated diminished diaphragmatic movement. Electromyography exhibited a failure of diaphragmatic response to phrenic nerve stimulation in 8 patients. All patients were mechanically ventilated; tracheostomy was required in 5 patients. Physiotherapy was considered a beneficial adjuvant measure. Diaphragmatic plication was attempted without success in 3 children. Seven children recovered without sequelae: Partial respiratory autonomy was achieved after an average of 2.6 months, complete autonomy after an average of 5.4 months. Two patients developed chronic lung disease; one of them remains unresponsive, and one child died following accidental extubation. We conclude that the diagnosis of diaphragmatic paralysis is predominantly clinical, and that the outcome of patients treated by adequate endotracheal mechanical ventilation is usually favorable.

Congenital muscular dystrophy with merosin deficiency

Congenital muscular dystrophy is one of the most frequent and severe childhood muscular dystrophies. Several forms of this disease have been described. The form associated with marked central nervous system disturbances, frequent in Japan, is known as Fukuyama congenital muscular dystrophy and was recently linked to chromosome 9. The most frequent form observed in occidental countries appears to be clinically characterized by exclusive involvement of skeletal muscle, and has been identified by clinico-pathological features which are often fallacious. A predominant histopathological feature is the marked increase in endomysial collagen tissue. We investigate whether laminin, a major component of the extracellular matrix, which is linked to the subsarcolemmal cytoskeleton by a large oligomeric complex of dystrophin-associated glycoproteins, could be involved in this form. We observed a specific absence of merosin, the laminin M chain, in 13 patients affected by classical non-Japanese form of congenital muscular dystrophy. This result allows the precise identification of a particular form of congenital muscular dystrophy and gives a clue to understanding its molecular pathogenesis.

Ondine's curse: a discussion of five cases

Five cases of central congenital hypoventilation, Ondine's curse, were studied. The diagnostic criteria were: lack of respiratory autonomy during sleep, abnormal CO2 test results and abnormal respiratory monitoring results during sleep. This hypoventilation induced chronic complications, such as a pulmonary arterial hypertension and psychomotor and/or growth retardation. The other conditions frequently associated with Ondine's curse were: brainstem disturbances, Hirschsprung disease and neuroblastoma. Since other brainstem dysfunctions are sometimes associated with hypoventilation and because complications can arise, these children routinely underwent complementary investigations. Treatment was symptomatic. Assisted mechanical ventilation was initiated as soon as possible and carefully monitored. The prognosis for these children has greatly improved and some of them lead a normal life with nightly assisted ventilation at home.

[Acute quinine poisoning treated with high dose of diazepam]

BACKGROUND

High concentrations of quinine, the drug of choice for severe malaria, are toxic to the cardiovascular system, producing hypotension and abnormal myocardial conduction.

CASE REPORT

An 8 year-old girl was admitted for fever, headache and arthralgias. Examination of a thick film of blood showed Plasmodium falciparum (parasitemia: 2%). She was given quinine intravenously. Ventricular tachycardia (150/min) and status epilepticus were seen 48 hours later, necessitating ventilatory support, plasma volume expander and IV sodium thiopental. On admission to an intensive care unit, the patient had hypothermia, was comatose (stage IV) with a reactive mydriasis and bradycardia (30/min). ECG confirmed bradycardia and showed a widened QRS complex. There was also a bilateral retinal edema. The blood level of quinine was 61 mumol/liter (therapeutic levels: 6-15). Retrospective inquiry revealed that the quinine initially administered had been incorrectly diluted. The child was treated with furosemide and adrenaline, followed by dobutamine and albumin infusion. She was then given diazepam (initial dose: 2 mg/kg then 6 mg/kg/day divided into 4 doses) intravenously, plus lidocaine, methylprednisolone and glycerol. The sinusal rhythm became normal 1 hour after the first bolus of diazepam. Consciousness gradually improved over the 10 days after admission while treatment was progressively discontinued. There were no sequelae, except for a transitory bilateral blindness.

CONCLUSION

The cardiovascular side-effects of quinine poisoning can be reversed with diazepam, as has previously been reported in cases of chloroquine poisoning.

[Respiratory form mof myasthenia gravis]

BACKGROUND

Extraocular, facial, bulbar and intercostal muscles are frequently affected in juvenile myasthenia gravis, especially during exacerbations. Acetylcholine receptor antibodies are often present in the blood in this type of myasthenic syndrome.

CASE REPORT

A girl presented with an exertional dyspnea at the age of 13 years, that improved after rest. All investigations were negative, except for lung function tests that showed a restrictive pattern. The diagnosis of juvenile myasthenia gravis was finally made at the age of 15 years because of the recurrence of sudden exertional dyspnea and a history of subtle weakness on repetitive movement leading to poor suckling, together with vocal and occasional swallowing difficulties. Dyspnea immediately improved after intravenous injection of 1 mg neostigmine, but the response was transient. No acetylcholine receptor antibody was found and a search for thymoma proved negative. Ambenonium chloride (Mytelase) was effective on clinical exacerbations, but the only improved test after 9 months of treatment was the functional residual capacity.

CONCLUSION

Anticholinesterase drugs must be tried in patients who present exertional dyspnea without bronchopulmonary or cardiac disease on the presumption of myasthenia gravis even when ocular or bulbar manifestations are absent.

[Whooping cough with Bordetella parapertussis isolation in an HIV positive child]

The authors report a case of whooping cough revealed by a pneumothorax in a 4 year-old boy with human immunodeficiency virus infection. Systemic signs of whooping cough were present. Bordetella parapertussis was isolated. Worsening of the HIV infection occurred simultaneously.

Gene for chronic proximal spinal muscular atrophies maps to chromosome 5q

Proximal spinal muscular atrophies represent the second most common fatal, autosomal recessive disorder after cystic fibrosis. The childhood form is classically subdivided into three groups: acute Werdnig-Hoffmann (type I), intermediate Werdnig-Hoffmann disease (type II) and Kugelberg-Welander disease (type III). These different clinical forms have previously been attributed to either genetic heterogeneity or variable expression of different mutations at the same locus. Research has been hindered because the underlying biochemical defect is unknown, and there are insufficient large pedigrees with the most common and severe form (type I) available for study. Therefore, we have undertaken a genetic linkage analysis of the chronic forms of the disease (types II and III) as an initial step towards the ultimate goal of characterizing the gene(s) responsible for all three types. We report here the assignment of the locus for the chronic forms to the long arm of chromosome 5 (5q12-q14), with the anonymous DNA marker D5S39, in 24 multiplex families of distinct ethnic origin. Furthermore, no evidence for genetic heterogeneity was found for types II and III in our study, suggesting that these two forms are allelic disorders.

[Oxygen therapy and assisted ventilation in children at home]

Home oxygen therapy is indicated in children with chronic obstructive lung disease when the oxygen content of arterial blood is decreased (oxygen partial pressure less than or equal to 50 mmHg). Three systems are available: compressed gas, bulk liquid, and oxygen concentrator. Oxygen may be administered via nasal cannulae, masks, hoods or endotracheal tubes 15 hours per day. FIO2 and SaO2 are periodically measured. Since 1972, when the experience of mechanical ventilation at home began with poliomyelitis teenagers, many children with neuromuscular diseases have been discharged from hospital with a ventilator. More recently, younger children with chronic lung diseases have also managed at home using intermittent positive pressure ventilation. Oral mechanical ventilation using pressure preset ventilators has been used in neuromuscular diseases; early and daily ventilation of children with paralytic respiratory muscles provides better development of the thoracic cage and of the lungs. Artificial ventilation can be performed by external means; we consider this type of ventilation as contraindicated as it causes thoracic deformities in young children.

[Diffusion of vancomycin in the cerebrospinal fluid, in the dog, in the absence of meningeal inflammation]

The diffusion of vancomycin into the cerebro-spinal fluid was studied in 5 healthy dogs. Its appears that vancomycin does diffuse across the blood-brain barrier. Though the concentrations reached in the CSF are low, they are of the same order of magnitude as the minimal inhibitory concentrations of this antibiotic towards the germs usually treated. The usual pharmacokinetic parameters were determined.

[Endocarditis of the ventricular septum. Echocardiographic diagnosis]

A 5 year-old child presented with prolonged fever, severe impairment of general condition and a pleuro-pericardium effusion. Echocardiography revealed a "bell-clapper-like tumor" in each ventricle, developed from the ventricular septum. Presence of a staphylococcal sepsis and early disappearance of the echocardiographic signs after antibiotic treatment allowed for diagnosis of bacterial endocarditis with abscess of the ventricular septum. Sinusitis and IgA deficiency were later found to be also present.

[Ventricular staphylococcal infections. Treatment with vancomycin by continuous venous infusion]

Thirteen cases of meningeal and/or ventricular infection and 1 case of septicaemia, all caused by staphylococci, were treated with continuous intravenous infusions of vancomycin. Repeated measurements of vancomycin plasma and CSF levels by microbiological assay or by high performance liquid chromatography showed that the antibiotic entered the CSF after 48 hours of treatment and that its concentrations in CSF remained stable at 1 to 4 micrograms/ml (mean: 2 micrograms/ml) throughout the 3 weeks' treatment period. After treatment was discontinued, vancomycin became undetectable in CSF within less than 24 hours. All the children were cured.