Infantile fibre type disproportion, myofibrillar lysis and cardiomyopathy: a disorder in three unrelated Dutch families

Neuromuscular Disorders 8 (1998) 296–304

Infantile fibre type disproportion, myofibrillar lysis and cardiomyopathy: a disorder in three unrelated Dutch families Peter G. Barth a ,*, Ronald J.A. Wanders b, Wim Ruitenbeek c, Charles Roe d, Hans R. Scholte e, Hans van der Harten f, Joan van Moorsel g, Marinus Duran h, Koert P. Dingemans i a

Departments of Pediatrics and Neurology, Emma Children’s Hospital/AMC, University of Amsterdam, PO Box 22700, 1100 DE Amsterdam, The Netherlands b Department of Pediatrics, Laboratory of Genetic-Metabolic Disease, Emma Children’s Hospital/AMC, University of Amsterdam, Amsterdam, The Netherlands c Department of Pediatrics, University Hospital St. Radboud, Nijmegen, The Netherlands d Institute for Metabolic Disease. Baylor University Medical Center, 3812 Elm Street, Dallas, TX 75226, USA e Department of Biochemistry, Erasmus University, Rotterdam, The Netherlands f Institute of Pathology, Free University Hospital, Amsterdam, The Netherlands g Department of Pediatrics, Laboratory for Metabolic Disease, Free University Hospital, Amsterdam, The Netherlands h University Children’s Hospital, ‘Wilhelm ina Kinderziekenhuis’, Nieuwe Gracht 137, Utrecht, The Netherlands i Department of Pathology (Electronmicroscopy), Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands Received 22 December 1997; revised version received 25 February 1998; accepted 4 March 1998

Abstract An apparently new cardioskeletal myopathy is reported in three unrelated families. Five infants were affected by rapidly progressive generalized muscle weakness, with onset shortly after birth, and dilated cardiomyopathy. All had generalized tremor (clonus) starting in the first week of life. The disease was lethal in all cases between 4 and 6 months. Muscle biopsy, performed in four of the five patients, showed a light microscopic pattern of small type I and normal-sized type II fibres. By electron microscopy small fibres were affected by myofibrillar disruption and swelling of organelles. Findings in blood and urine suggested a disturbance in energy metabolism but an extensive search for respiratory chain disorders and disorders of mitochondrial fatty acid oxidation in frozen muscle and cultured fibroblasts was negative. The findings support a new progressive autosomal recessive infantile cardioskeletal myopathy in which type I muscle fibres are preferentially affected.  1998 Elsevier Science B.V. All rights reserved Keywords: Infantile fibre type disproportion; Myofibrillar lysis; Cardiomyopathy

1. Introduction Selective hypotrophy of type I muscle fibres is found in congenital fibre type disproportion [1] defined as a distinct, relatively benign congenital myopathy. Other infantile neuromuscular disorders were subsequently shown to display this histologic feature, including congenital myotonic dystrophy [2], infantile Krabbe’s disease [3,4], infantile Pompe’s disease [3] and nemaline myopathy [5]. It has also become associated with congenital cerebral disorders including Lowe syndrome [6] and Marden–Walker syn* Corresponding author. Tel.: +31 20 5662851; fax: +31 20 6917735; e-mail: [email protected]

0960-8966/98/$19.00  1998 Elsevier Science B.V. All rights reserved PII S0960-8966 (98 )0 0028-5

drome [7]. Selective muscle fibre type I hypotrophy was found in association with tubular aggregates, cardiomyopathy and myasthenic features in one family [8]. An important and growing number of genetic cardioskeletal myopathies result from impaired energy metabolism, including glycogen storage disorders, mitochondrial b-oxidation defects and respiratory chain disorders (for recent reviews see Refs. [9,10]). Morphological findings in these disorders do not include selective involvement of type I fibres, except for a report on infantile lactic acidosis with CNS involvement, an absence of cardiac involvement and a benign course [11] subsequently associated with pyruvate dehydrogenase complex dysfunction [12] and selective type I atrophy in carnitine palmitoyltransferase deficiency with atypical pre-

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2. Materials and methods

Fig. 1. Pedigrees of the three affected families.

sentation in an adult [13]. We were unable to find previous reports on a disease pattern of dilated cardiomyopathy and morphological changes preferentially affecting type I fibres. We studied five children from three families who were born in the period between 1980 and 1990 with an apparently identical syndrome of early onset progressive neuromuscular disorder with the morphometric features of fibre type disproportion, degenerative changes in small type I skeletal muscle fibres and dilated cardiomyopathy.

Patients included in this study met the following criteria: (1) a positive family history for similarly affected siblings of either sex; (2) early postnatal onset of generalized tremor; (3) progressive dilated cardiomyopathy; (4) progressive neuromuscular weakness; (5) death from cardiac failure between 4 and 6 months after birth; (6) a pattern of fibre type disproportion and myofibrillar lysis in type I muscle fibres in biopsied muscle. Pedigrees of the three affected families are shown in Fig. 1. Table 1 lists the five patients according to admission number (first row) and pedigree numeral (second row). Clinical evaluation and follow-up was performed by one of the authors (P.G.B.). Data from patient 4 were made available through hospital records. This patient was not biopsied, but clinical and laboratory data were included because of a striking resemblance to her affected sister (patient 5). Blood samples for determination of lactic acid were either arterial samples or venous samples drawn from an indwelling catheter. A full autopsy was performed in patient 1. Muscle biopsies were taken from the quadriceps muscle and frozen sections were prepared according to standard techniques in patients 1, 2, 3 and 5. Fibre diameter histograms were prepared according to methods previously described [14] from sections stained for routine ATPase at pH 9.4. This ATPase was chosen because it afforded the best comparison between individual biopsies which came from different laboratories. A single area was sampled from

Table 1 The clinical profile and biochemical findings in body fluids Patient

1a

2a

3

4b

5b

Pedigree/sibling number Sex Birth weight (kg) General tremor/clonus Progressive generalized paresis Dilated cardiomyopathy Age at death (months) Terminal multiorgan failure Biochemistry Ketonuriac Dicarboxylic acids in urinec Routine During terminal crisis Total ketone bodies (mmol/l serum) following overnight fast Creatine kinase (U/l) (normal ,100) Hypoglycaemia following ≥8 h fastc Blood glucose during terminal crisis (mmol/l)

A/1 Male 2.7 + + + 6 −

A/2 Female 2.5 + + + 6 −

B/10 Female 3.9 + + + 5 −

C/1 Female 3.5 + + + 4 +

C/2 Female 3.6 + + + 5 +

0/1 1/1 C6,C8,C10 ND ND 50 0/1 1.8

2/6 3/6 C6,C8,C10 ND 2.15 (12 h) 26 0/8 ND

0/1 0/1 – ND 2.73 (16 h) 134 0/2 7.4

1/1 1/1 ND C6,C8,C10 0.44; 0.92 12400d ND 1.3

Lactic acidaemia (>2.2 mmol/l serum) after overnight fastc Observation range (mmol/l)

0/1 1.92

6/8 1.45–3.30

1/2 1.70–3.92

2/2 5.00–9.30

1/2 1/2 – C6 ND 1733d ND Normal during i.v. glucose ND ND

ND, not done. Affected siblings. c Times present/times examined. d During metabolic crisis. a,b

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each biopsy containing at least 100 fibres of either type. Sections stained for myosine ATPase preincubated at pH 4.3 and 4.6 were reviewed for subclassification of type II fibres. Additional frozen sections were routinely stained for NADH–oxidoreductase, succinate dehydrogenase, PAS, PAS after diastase digestion, oil red O, haematoxylin and eosin and Gomori trichrome. Suitable blocks were prepared for electron microscopic examination. A muscle biopsy of patient 5 was frozen in liquid nitrogen and activities of mitochondrial complexes and PDHC complex were measured as previously described [15,16]. Activities of mitochondrial respiratory chain complexes were measured in cultured skin fibroblasts as described previously [17]. Acyl-CoA dehydrogenase activities were measured [18] using the ferricenium method. Hydratase, 3hydroxyacyl-CoA dehydrogenase and 3-oxoacyl-CoA thiolase activities were measured [19] using substrates of different chain length. Carnitine palmitoyltransferase 1 and 2 were measured essentially as described previously [20]. Acylcarnitine profiling was used to determine overall boxidation activities in growing fibroblasts as previously described [21]. Immunoblot analysis for electron transfer flavoprotein (ETF) was performed in fibroblast material of patient 5 as previously described [22].

3. Results 3.1. Clinical profile The pedigrees of the three families (A–C) are depicted in Fig. 1. Clinical findings and clinical biochemistry are shown in Table 1. All patients were born with a normal body length and birth weight. Vital signs (Apgar scores) were normal. In all patients the first symptom was generalized coarse tremor or clonus, not associated with hypoglycaemia or hypocalcaemia, present in the first week of life and gradually becoming less pronounced. Generalized muscular hypotonia and weakness developed in all patients soon after birth, resulting in progressive head lag and failure of antigravity responses. Facial weakness with tented upper lip was seen in patients 1–3. Ptosis developed in patients 1 and 2. Muscle tendon reflexes were initially retained and hyperactive but were lost subsequently. Patients 4 and 5 were not seen by a paediatric neurologist before a terminal stage was reached, but their records mention early onset of generalized and progressive weakness. Progressive cardiac failure was present in all patients investigated and was due to dilated cardiomyopathy, with unilateral (right- or left-sided) or bilateral atrial dilatation. Echocardiographic examinations in patients 2, 3 and 5 showed signs of myocardial hypoactivity, diminished shortening fraction and dilatation of one or both ventricles. Cardiac hypertrophy was absent. Electrocardiographic signs of myocardial strain were present in all patients. All patients died from cardiac decompensation and shock following progressive cardiac dilatation. While signs

Fig. 2. Diameter histograms of muscle fibres of patients 1, 2, 3 and 5 based on myosine ATPase (pH 9.4).

of cardiac strain were present early in the course of the disease, decompensation only appeared during the last month of life in all patients. In patients 4 and 5 the terminal course was influenced and possibly prolonged by intensive care treatment. These two patients developed multiorgan failure following cardiac decompensation and shock, accompanied by metabolic acidosis, generalized seizures, coagulation disturbances, generalized liver failure with hyperammonemia and massive elevation of creatine kinase. The history of the second child of pedigree B, as related by the parents, strongly suggests the same disease with neonatal onset of tremor, progressive generalized neuromuscular

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P.G. Barth et al. / Neuromuscular Disorders 8 (1998) 296–304 Table 2 Diameters of type I and type II fibres, fibre type disparity and variability coefficient Patient

1

2

3

5

Type I (m1 ± SD) Type II (m2 ± SD) 100(m2 − m1)/m2 (%)a Variability coefficient SD/m × 1000b Relative frequency of type I (%)

6.0 ± 3.3 17.8 ± 3.6 66 I:550 II:202 70

4.9 ± 3.3 13.0 ± 1.6 62 I:673 II:123 69

10.2 ± 4.3 17.1 ± 6.4 40 I:421 II:374 48

7.6 ± 3.5 14.0 ± 2.8 46 I:466 II:200 79

Diameters are given in mm. m1, m2, means of diameters of type I and type II fibres, respectively. Measure of diameter disparity between fibre types, with m1 and m2 representing types I and II, respectively; normal value ,12%, see Ref. [23]. b Normal value >250 for both types. a

weakness and death at the age of 5 months. However, cardiac evaluation and muscle biopsy were not performed. A full autopsy was performed on patient 1. 3.2. Neuromuscular pathology The main abnormality on light microscopy in each case was a discrepancy in size between small-sized type I fibres and normal-sized type II fibres, histographically illustrated in Fig. 2. Means and standard deviations for type I and type II fibres (Table 2) prove the large difference in size between these two populations. The equation 100(m2 − m1)/m2 indicates the size disparity, where m1 and m2 represent the mean diameter of the respective types. The result should be less than 12% as a measure of the difference between the fibre types [23]. The findings in the present patients vary between 40 and 66%. Variability in the diameter is given by the variability coefficient SD/m × 1000. This variable exceeds the value of 250 for type I fibres in all biopsies, while the type II fibres are below this value in three of four biopsies. A predominance of type I fibres was also present in patients 1, 2 and 5, but absent in patient 3. Findings meet the morphometric criteria for congenital fibre type disproportion as proposed by Brooke [1] completely in three and partially in one of the four biopsies, the exception being patient 3 with increased variability present also in type II fibres. Control data for the neonatal period by Colling-Saltin [24] are as follows: type I, 14.7 ± 3.1 mm; type IIA, 16.8 ± 3.2 mm; type IIB, 17.0 ± 3.1 mm. Type I fibres in the present patients (Table 2) are too small when compared to these neonatal values, while biopsies were taken between the ages of 0.2 and 0.5 years. Type II fibres are close to the neonatal range, but also fit the normative data provided by Brooke and Engel [23] for the postnatal period. Fig. 3A illustrates the findings on myosin ATPase staining after preincubation at pH 4.3 in patient 3. Comparison of the three myosin ATPase stains used showed that a small proportion (less than 5%) belonged to type IIC. In all biopsies the proportion of type IIB versus type IIA was diminished, but the proportions differed per fascicle and were therefore difficult to quantify. Some increased NADH-oxidoreductase activity in the smallest type I fibres present was obvious in all biopsies, as

shown in Fig. 3B. An increased number of neutral fat droplets, mainly in type I fibres, was seen in all biopsies (Fig. 4A), except for patient 3, where both fibre types displayed a mild increase of lipid droplets. A complete absence of stainable glycogen was found in the biopsies of patients 1 and 5, who were in the final stage of their disease (Fig. 4B). This finding may reflect an increased dependence on anaerobic glycolysis at the time of the biopsy. Electron microscopy of

Fig. 3. Patient 3. Quadriceps femoris muscle at age 0.2 years. Frozen sections (×230). (a) Myosine ATPase preincubated at pH 4.3. Note the small size and increased variability of type I fibres. (b) NADH-oxidoreductase. Smallest type I fibres show disproportionate high activity, probably due to degeneration.

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was a loss of myocardial myofibrillar structure without signs of storage or inflammation. Post-mortem electron microscopy showed numerous mitochondria without clear structural defects, except for signs of autolysis. The kidneys were smaller than normal; the weight of both kidneys was 39.5 g (normal 66 ± 14 g). Histology showed no abnormalities. The liver showed acute congestion. The brain weight was 850 g (normal 773 ± 95 g). It showed a minimal dilatation of the lateral ventricles. Myelination appeared appropriate for the age of the patient. The cerebral cortex, thalamus, basal ganglia and brainstem and cerebellum were normally developed. Anterior horn cells in the spinal cord at various levels appeared to be of normal size and

Fig. 4. Patient 5. Quadriceps femoris muscle at age 0.5 years, shortly before death. Frozen sections (×330). (a) Oil red O stain. Accumulation of neutral lipid droplets in small type I fibres. (b) PAS stain shows complete glycogen depletion in all muscle fibres.

all the biopsies was similar. Severely affected small fibres showed variable Z-band streaming and myofibrillar lysis, loss of triads and swollen mitochondria, while neighbouring larger fibres were normal or minimally affected (Figs. 5 and 6). Incidental Z-band thickenings were encountered but did not reach the size of a sarcomere and on higher magnification did not show the lattice structure which is characteristic for rods in patients with nemaline myopathy [25]. In addition, rods were not found in myonuclei on extensive screening. A sural nerve biopsy taken from patient 4 was embedded in epon. Transverse 1 mm sections stained with Toluidine Blue showed a normal picture that was appropriate for the age of the patient. 3.3. Autopsy findings (patient 1) The heart weighed 54.7 g (normal 44 ± 8 g). It showed bilateral dilatation with normal anatomy and slight hypertrophy. Histology showed vacuolization of the heart muscle cells and subendocardial foci of fibrinoid necrosis. There

Fig. 5. Electron microscopy of muscle (quadriceps) of patient 3. The transverse and slightly oblique section shows a population of normalsized and small-sized fibres. No abnormalities are seen in the normalsized fibres while the small fibres show sarcomeric disorganization (×2100).

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Fig. 6. Electron microscopy of muscle (quadriceps) of patient 5. The longitudinal section shows three muscle fibres and a longitudinally sectioned capillary. The fibre in the left upper quadrant shows the normal aspect of sarcomeres, sarcoplasma, mitochondria and triads. The fibre in the right lower quadrant shows a normal sarcomere structure, some swollen mitochondria and lipid droplets. The small-sized muscle fibre in the centre of the photograph shows severe myofibrillar loss, lipid droplets and swollen mitochondria (×7900).

numbers. Clarke’s column appeared hypertrophic relative to the anterior horns. Otherwise there were no abnormal findings in the central nervous system. Detailed examination of one eye did not reveal abnormalities. 3.4. Biochemistry Findings in body fluids are shown in Table 1. A mild and variable lactic acidaemia was observed in patients 2 and 3 in periods of relative well-being that was not influenced by cardiac failure. Fasting provoked normal ketogenesis with normoglycaemia. In patients 2 and 4 increased ketonuria and increased excretion of dicarboxylic acids was observed during the same sampling periods, indicating that stimulation of Q-oxidation does not signify impairment in the mitochondrial b-oxidation pathway. Free serum/plasma lcarnitine was normal in all patients. Quantitative amino acid excretion patterns were normal in all patients. Quantitative organic acid pattern analysis by gas chromatography/

mass spectrometry showed mild elevations of 2-oxoglutaric acid and citric acid in patients 1 and 2. Table 3 Mitochondrial respiratory chain, PDH-complex and carnitine in muscle (patient 5) Enzyme activity

Patient

Control range

NADH: Q1 oxidoreductase Succinate: cyt c oxidoreductase Cytochrome c oxidase Citrate synthase Pyruvate DH complex (PDHC) E1 component of PDHC E3 component of PDHC Total carnitine Free carnitine

12 12 134 166 1.6 0.09 126 2.7 2.3

4.7–19 4.2–16 73–284 48–146 2.8–6.2 0.10–0.25 65–199 2.7–4.6 2.2–4.2

Activities are expressed in mU/mg protein, E3 is expressed in mU/mg protein and carnitine is expressed as mmol/g wet weight.

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Table 4

Table 6

Pyruvate dehydrogenase complex and respiratory chain in fibroblasts

Mitochondrial fatty acid oxidation in muscle (patient 5)

Patient

Enzyme activity

PDH complex Pyruvate DH complex basala Pyruvate DH complex totala Respiratory chain and SDH NADH: Q1 oxidoreductaseb Succinate dehydrogenaseb Succinate: cyt c oxidoreductaseb Decylubiquinol: cyt c oxidoreductaseb Cyt c oxidasec Citrate synthasec a

2

3

49 79

5

49 60

Controls

64 81

0.18

0.14

0.16 0.30

0.14 0.35

0.14 0.067–0.18 0.31 0.21–0.44

1.78

2.06

1.34

181 276

159 230

209 276

Carnitine palmitoyltransferase 1 Carnitine palmitoyltransferase 2 Acyl-CoA dehydrogenase, C16 Enoyl-CoA hydratase C4 C12 Ratio C12/C4 3-Hydroxy-acyl-CoA dehydrogenase C4 C16 Ratio C16/C4 Thiolase C4, − K C4, + K Ratio + K/ − K C16 Glutamate dehydrogenase

21–87 22–139

0.16

0.10–0.26

1.25–2.62 147–252 144–257

nmol/h per mg protein. mU/mU cytochrome c oxidase. mU/mg protein (enriched mitochondrial fraction).

b c

Patient

Results of respiratory chain studies in muscle and fibroblasts are given in Tables 3 and 4, respectively. Results of mitochondrial b-oxidation in fibroblasts and muscle are given in Tables 5 and 6, respectively. Activities of respiratory chain complexes I–IV and pyruvate dehydrogenase in muscle of patient 5 (Table 3) do not indicate abnormalities. Similarly normal results were obtained in fibroblasts from patients 2, 3 and 5 (Table 4). Mitochondrial b-oxidation enzyme studies performed in muscle from patient 5 (Table 6) exclude the deficiency of one muscle specific isoenzyme subserving mitochondrial boxidation in muscle. Mitochondrial b-oxidation was studied in fibroblasts of patients 2, 3 and 5 by carnitine profiling as shown in Table 5. No gross excess of any intermediate was shown, ruling out deficiencies of carnitine/acylcarnitine translocase, carnitine palmitoyltransferase I and II, very long chain acyl-CoA dehydrogenase, long chain acyl-CoA dehydrogenase, medium chain acyl-CoA dehydrogenase, short chain acyl-CoA dehydrogenase and severe deficiency of electron transfer (ETF) dehydrogenase. The latter possibility was more specifically ruled out in fibroblast assays of oxidation of [9,10-3H]palmitate and [9,10-3H]myristate and by the presence of ETF cross reactive material in fibroblasts of patient 3 (Table 5).

Controls

0.29 14.2 28.9

0.24; 0.13 4.06; 3.47 15.2; 16.7 (n = 4) 481 ± 236 94 ± 35 0.21 ± 0.07 (n = 4) 353 ± 145 102 ± 31 0.31 ± 0.07 (n = 4) 9.8 ± 4.3 55 ± 32 5.3 ± 1.8 14 ± 8 15.0; 20.5

533 159 0.30 401 162 0.40 15.4 55.1 3.6 12.5 74.0

All activities are expressed in nmol/min per mg protein.

4. Discussion Three families are described, each with two affected children. No similar disease is present in the parents and both sexes are affected. Therefore, the disease is most probably an autosomal recessive disorder. The disorder is progressive in all cases that were seen by us and affects cardiac and skeletal muscle. Central nervous system involvement is suggested by the characteristic tremor, resembling the wellknown clonus or jitteriness of neonates with hypoglycaemia or hypocalcaemia, excluded in all the patients. Besides terminal stage involvement there were no other pointers to central nervous system involvement. Patients were alert during the major part of their lives. Brain imaging, electroencephalography and evoked responses were normal in three patients seen by one of the authors during the early course of their disease. Two patients developed multiorgan failure as a terminal manifestation. It is not clear whether this complication was the single result of cardiogenic shock, or if it should be ascribed to direct involvement of other organs outside the neuromuscular and cardiac systems by

Table 5 Mitochondrial b-oxidation in fibroblasts Patient

2

3

5

Controls

Acylcarnitine profiling in growing fibroblasts

Slight decrease of acetylcarnitine

Slight decrease of acetylcarnitine 3.57 7.27 Normal CRMb

Normal

Normala

Oxidation of [9,10-3H]palmitate without carnitine (nmol/h per mg) Oxidation of [9,10-3H]myristate with carnitine (nmol/h per mg) ETF Western blot a

Ref. [21]. Cross-reacting material.

b

3.76–6.24 5.91–13.91

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the unknown basic defect. However, a similar complication may ensue in known disorders of mitochondrial b-oxidation, often provoked by intercurrent infection. Muscle morphology in the present disease is unique in combining the histologic characteristics, well-known in so-called congenital fibre type disproportion with signs of myofibrillar lysis, almost exclusively in the small type I fibres. Previous descriptions of muscular ultrastructure in cases diagnosed as congenital fibre type disproportion allude to a normal structure [3], or small foci of myofibrillar disarray (case 1 in Ref. [26]; [27,28]). Because of the dynamic character of the present disease it is uncertain whether the findings would be similar to congenital fibre type disproportion at all stages, including the perinatal period. Therefore, we prefer to call it infantile fibre type disproportion, emphasizing the stage of the disease at which biopsies were taken. Energy requirements of cardiac muscle mostly reflect those of type I fibres, with a strong dependence on mitochondrial energy conservation. It is indeed remarkable to find a combined involvement of cardiac muscle and skeletal muscle with predominant affection of type I fibres in the present disease. This combination warrants a search for deficiencies in mitochondrial b-oxidation and the respiratory chain. Some of our findings indeed strongly support the involvement of energy metabolism, i.e. (1) intermittent mild lactic acidosis, not explained by cardiac failure, (2) histochemical evidence of glycogen depletion in skeletal muscle in the terminal phase of the disease and (3) multiorgan failure and highly increased plasma creatine kinase activities in patients 4 and 5. However, an extensive search for mitochondrial respiratory chain dysfunction and mitochondrial b-oxidation dysfunction undertaken in skeletal muscle and cultured skin fibroblasts gave normal results. Inherited disorders of mitochondrial b-oxidation include deficiencies of carnitine palmitoyl-transferase II [29,30], very long chain acyl-CoA dehydrogenase [31], trifunctional enzyme [32], long chain 3-hydroxyacyl-coenzyme A dehydrogenase [33] and short chain l-3hydroxyacyl-CoA dehydrogenase [34]. Generally, defects of energy conservation may lead to impaired ability to maintain a transmembrane Ca-gradient, causing Ca-influx with resulting muscle necrosis. This mechanism has not been ruled out by the present investigations. Therefore, despite the normal biochemical findings pertaining to mitochondrial respiratory chain and mitochondrial b-oxidation in muscle and fibroblasts, a defect in energy metabolism cannot be definitely ruled out at this stage. A unique and unexplained finding is the preference of the myofibrillar lysis of type I fibres. The destruction of type I fibres may offer an explanation for the small size of type I fibres in this disorder. It may be hypothesized that these fibres become involved by destruction soon after their differentiation from type IIC fibres and before attaining their age-appropriate size. An increased turnover of type I fibres relative to type II fibres might result in increasingly severe disproportion between the two types.

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Acknowledgements The authors acknowledge the expert help of Professor F.A. Jennekens, Neuromuscular Laboratory of the University of Utrecht, for nerve biopsy studies in patient 5, Professor H.F.M. Busch, Neuromuscular Laboratory of the University of Rotterdam, for sharing his results in patient 3, Dr. B. Garavaglia, Instituto Neurologico C. Besta, Milan, for the assays of ETF and ETF-DH in patient 5 and Dr. L. IJlst, Department of Pediatrics, Emma Children’s Hospital, Amsterdam, for the assay of b-oxidation enzymes in muscle. The contributions and fruitful discussions provided by Dr. G.D. Vos, intensive care paediatrician, and by Dr. R.J. Moene, Dr. L.J. Lubbers and Dr. J. Lam, paediatric cardiologists, are gratefully acknowledged. References [1] Brooke MH. Congenital fiber type disproportion. In: Kakulas BA, ed. Clinical Studies in Mycology. Proceedings of the Second International Congress on Muscle Diseases. Amsterdam: Excerpta Medica, 1973:147–159. [2] Karpati G, Carpenter S, Watters GV, Eisen AA, Andermann F. Infantile myotonic dystrophy. Histochemical and electron microscopic features in skeletal muscle. Neurology 1973;23:1066–1077. [3] Martin JJ, Clara R, Ceuterick C, Joris C. Is congenital fibre type disproportion a true myopathy? Acta Neurol Belg 1975;76:335–344. [4] Dekharghani F, Sarnat HB, Brewster MA, Roth SI. Congenital muscle fiber-type disproportion in Krabbe’s leukodystrophy. Arch Neurol 1981;38:585–587. [5] Schmalbruch H, Kamieniecka Z, Arroe M. Early fatal nemaline myopathy: case report and review. Dev Med Child Neurol 1987;29:784–804. [6] Kohyama J, Niimura F, Kawashima K, Iwakawa Y, Nonaka I. Congenital fiber type disproportion myopathy in Lowe syndrome. Pediatr Neurol 1989;5:373–376. [7] Garcia-Alix A, Blanco D, Caban˜as F, Sanchez PG, Pellicer A, Quero J. Early neurological manifestations and brain anomalies in Marden– Walker syndrome. Am J Med Genet 1992;44:41–55. [8] Dobkin BH, Verity MA. Familial neuromuscular disease with type I fiber hypoplasia, tubular aggregates, cardiomyopathy, and myasthenic features. Neurology 1978;28:1135–1140. [9] Kelly DP, Strauss AW. Inherited cardiomyopathies (review article). N Engl J Med 1994;330:913–919. [10] Schwartz ML, Cox GF, Lin AE, et al. Clinical approach to genetic cardiomyopathy in children. Circulation 1996;94:2021–2038. [11] Iso A, Murakami N, Yoneyama H, Hanaoka S, Kurokawa T, Nonaka I. Idiopathic lactic acidemia with developmental delay and type I muscle fiber atrophy: report of two patients. Brain Dev 1993;15:384–386. [12] Murakami N, Iso A, Naito E, Kuroda Y, Nonaka I. Thiamine responsive congenital lactic acidemia and type 1 muscle fiber atrophy (letter). Brain Dev 1995;17:78. [13] Shintani S, Shiigai T, Sugiyama N. Atypical presentation of carnitine palmitoyltransferase (CPT) deficiency as status epilepticus. J Neurol Sci 1995;129:69–73. [14] Dubowitz V. Definition of pathological changes seen in muscle biopsies. In: Dubowitz V, ed. Muscle Biopsy. A Practical Approach, 2nd edn. London: Baillie`re Tindall, 1985:82–128. [15] Fischer JC, Ruitenbeek W, Gabree¨ls FJM, et al. A mitochondrial encephalopathy: the first case with an established defect at the level of coenzyme Q. Eur J Pediatr 1986;144:441–444. [16] Sperl W, Trijbels JMF, Ruitenbeek W, et al. Measurement of totally

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