Abstract
Objective and Background: To describe three Gypsy families with Marinesco–Sjögren syndrome (MSS), demyelinating neuropathy, and recurrent episodes of myoglobinuria in five of the six affected subjects. Because these families originated from the same genetically isolated founder population as did patients with congenital cataracts facial dysmorphism neuropathy (CCFDN) syndrome, and because the two syndromes have clinical manifestations in common, we hypothesized that the two related, albeit distinct, syndromes may represent clinical variants of a single genetic disorder.
Methods: Clinical studies were conducted and linkage and haplotype analyses were performed for the three families. A total of 16 individuals, including the 6 with MSS and 10 unaffected relatives, were genotyped for six polymorphic microsatellite markers from the CCFDN region on 18qter.
Results: Linkage analysis of markers in the 18qter region, where we previously had located the CCFDN gene, produced a lod score of 3.55, demonstrating colocalization of the gene responsible for MSS with demyelinating neuropathy and myoglobinuria with the CCFDN gene. Moreover, the patients with MSS shared the conserved marker haplotype found in CCFDN chromosomes.
Conclusions: These data suggest that Marinesco–Sjögren syndrome with peripheral neuropathy and myoglobinuria, and congenital cataracts facial dysmorphism neuropathy syndrome are genetically identical and are caused by a single founder mutation.
Marinesco–Sjögren syndrome (MSS) (MIM 248800) is a rare autosomal-recessive disorder characterized by congenital cataracts, cerebellar ataxia, developmental delay, and mental retardation.1,2⇓ Additional features include short stature, skeletal deformities, hypogonadism, and variable neuromuscular manifestations such as chronic myopathy,3-6⇓⇓⇓ or motor and sensory neuropathy.7-9⇓⇓ The disorder occurs in patients of diverse ethnic backgrounds. The MSS gene’s location is unknown.
Congenital cataracts facial dysmorphism neuropathy (CCFDN) syndrome (MIM 604168) is another rare autosomal-recessive disorder whose cardinal features include congenital cataracts, characteristic facial features, and hypomyelinating motor and sensory neuropathy.10 Other manifestations include developmental delay, mental retardation, short stature, skeletal deformities, and hypogonadism.10 We identified and characterized CCFDN in Bulgarian Gypsy patients.10,11⇓ Previously, we mapped the CCFDN gene to chromosome 18qter.11 Related disease haplotypes in the same region suggested genetic homogeneity and a single founder mutation causing CCFDN.11
Despite considerable overlap between phenotypes, MSS and CCFDN have distinctive features. Cerebellar involvement is mandatory for the diagnosis of MSS but is rare and very mild in CCFDN; myopathy is present in MSS but not in CCFDN patients, whereas the severe hypomyelinating neuropathy and distinctive facial features are characteristic of CCFDN and not of MSS. These differences between the two syndromes have justified their classification as independent disease entities.
In 1998, we described12 four children from two unrelated Gypsy families from Germany who presented with classic symptoms of MSS and an unusual combination of neuromuscular manifestations. These patients had demyelinating peripheral neuropathy, together with dramatic, often recurrent episodes of acute parainfectious muscle weakness with myoglobinuria and creatine kinase (CK) levels as high as 40,000 U/L. This complex phenotype added acute myopathy to the list of possible neuromuscular manifestations of MSS.
This study describes another family with the same phenotype and a follow-up of the Gypsy families from Germany.12 The two newly diagnosed patients belong to an Italian Gypsy kindred. Both have peripheral neuropathy and one had acute parainfectious myoglobinuria. Our observations indicate that parainfectious myoglobinuria is a relatively common and potentially dangerous manifestation in Gypsy patients with MSS.
The families with MSS originate from the same genetically isolated founder population as do the aforementioned Bulgarian families with CCFDN.10,11⇓ This suggested that the two related, albeit distinct, syndromes may represent clinical variants of a single genetic disorder. To test this hypothesis, we conducted linkage and haplotype analyses in the Italian family and in the two families from Germany with MSS.12
Subjects and methods.
Subjects.
The study included three families, each with two patients affected with MSS. The Italian Gypsy patients belong to an extended kindred with complex consanguinity (figure 1). In the two German Gypsy families (see figure 1 in Müller-Felber et al.12), the parents were unrelated and each family had two affected children. Informed consent was obtained from all individuals involved. The study complied with the ethical guidelines of the participating institutions.
Figure 1. Pedigree of consanguineous Italian Gypsy kindred (left) to which Patients 1 and 2 belong. The affected individuals are homozygous for the highly conserved congenital cataracts facial dysmorphism neuropathy alleles for most markers except the most centromeric D18S461. One of the Gypsy families with Marinesco–Sjögren syndrome (right) was reported previously.12 Paternal recombination in Patient 3 is shown in the area shaded with diagonal lines.
Methods.
A total of 16 individuals, including the 6 with MSS and 10 unaffected relatives were genotyped for six polymorphic microsatellite markers from the CCFDN region on 18qter.11 Information on four of these markers, D18S461, D18S1095, D18S1390, and D18S70, is available on public genome databases. The other two markers, 23090ta and 1908ca1, were identified by searching the published sequence of genomic bacterial artificial chromosomes (BAC) clones mapping to the 18qter region. Polymerase chain reaction amplification was performed using fluorescently labeled primers. The products were size-separated on an ABI 377 automated DNA sequencer and analyzed with Genotyper software (PE Biosystems, Foster City, CA). Linkage analysis was performed under an autosomal-recessive model with 100% penetrance and a gene frequency of 0.01, using the GENEHUNTER program.13 Haplotypes on MSS chromosomes were constructed manually and compared with those derived from a study of 86 CCFDN chromosomes.
Results.
Clinical reports. Patients 1 and 2. Patient 1.
This boy was the second child of healthy consanguineous Italian Gypsy parents. The older sister was healthy. He had been delivered at term and birth weight was 2,990 grams. The neonatal period was uneventful. Cataracts were noted at 1 month and surgically treated at 5 months. The patient was hypotonic, and motor and speech development were delayed. He was able to walk at 18 months.
At age 2 years, he had acute weakness and inability to stand and walk, which developed after 2 days of fever and myalgia. Serum CK was 46,276 U/L (normal <195 U/L). CK values returned to normal in 10 days, and muscle function recovered after 1 month. A muscle biopsy specimen was obtained 6 days after the onset of muscle weakness and showed mild myopathic features with variations in fiber size and scattered necrotic fibers. No ragged red fibers were seen. Histochemical reactions were normal. Dystrophin, sarcoglycan, and laminin protein expression was normal. Subsequently, the patient developed an unsteady gait and had mild ataxia and nystagmus. On several occasions CK was normal.
At age 6 years, he had an upper respiratory tract infection with high fever and had diffuse myalgia. On the third day, he was unable to stand and was admitted to the hospital, where brown discoloration of the urine was noticed. Serum CK was 52,072 U/L and myoglobinuria of 1990 μg/L was present (normal <20). Neurologic examination 2 weeks after the acute episode revealed diffuse proximal weakness (Medical Research Council scale grade 3 [MRC 3]) and obvious wasting and weakness (MRC 2) of the hand, foot, and digit extensor muscles. He was able to stand but could not walk. Tendon reflexes were absent. Median motor nerve conduction velocity (NCV) was 25 m/s, distal latency was 3.3 ms, and compound muscle action potential (CMAP) amplitude was 4 mV. Median sensory NCV was 24 m/s, and sensory action potential amplitude was 20 μV. CK returned to normal by day 18 and myoglobinuria returned to normal by the sixth day. He had a steady recovery of function, and after day 20, he was able to walk with support. One month after the myoglobinuria resolved, he was able to walk without support but had an ataxic gait. Proximal muscle weakness was less severe (MRC 4), whereas the distal weakness remained unchanged.
The patient had peculiar facial features with some thickening of the upper lip (figure 2). Head circumference was 47.3 cm (<3rd percentile), height 110.6 cm (10th percentile), weight 14.650 kg (3rd to 10th percentile). Brain MRI findings were normal.
Figure 2. Portraits of Patients 1, 5, and 6, respectively. Note that the distinctive facial features are not obvious in early childhood and become more evident in adolescence. All patients have mild ptosis and show similar midface features with thick upper lips and prominent noses and upper front teeth.
Patient 2.
The second patient belongs to the same Italian Gypsy kindred (see figure 1). She is the first child of a consanguineous marriage. The other sibling is unaffected. During pregnancy, reduced intrauterine movements were noticed. Delivery was at term and uneventful. Birth weight was 2,750 grams. Cataracts were recognized at 1 month and the patient underwent surgery three times. Additional ophthalmologic symptoms included microphthalmia and nystagmus. Early motor and cognitive development were delayed. The patient started walking at 2.5 years of age, with an ataxic gait. She had mild mental retardation. No episodes of parainfectious muscle weakness or urine discoloration have been reported.
Examination at age 8 years revealed mild ataxia, nystagmus, mild muscle weakness, severe equinus deformity, and mild scoliosis. Median motor NCV was 27 m/s, distal latency was 3.0 ms, and CMAP amplitude was 8 mV. Ulnar motor NCV was 28 m/s, distal latency was 2.7 ms, and CMAP was 11.9 mV. Median sensory NCV was 30 m/s, and sensory action potential amplitude was 10 μV. Serum CK, long chain fatty acids, amino acids, lactic, and pyruvic acid levels were normal.
Patients 3 and 4.
Patients 3 and 4 are siblings and have been reported previously12 (Patients G.A. and G.D. in the original reference). In brief, they are the first and third children of healthy, nonconsanguineous Gypsy parents. The second child is unaffected.
Patient 3.
The clinical and electrophysiologic findings for this child, up to age 12, are described in the original publication.12 Subsequently, the boy had three episodes of acute weakness and elevated serum CK after febrile infections. The duration between onset of weakness and recovery ranged between 4 weeks and 1 year. Furthermore, distal and symmetric polyneuropathy progressed steadily leading to severe deformity of both feet and hands. The boy underwent surgical correction of the equinovarus deformity of his feet at ages 15 and 17.
At reexamination at age 18, peculiar facial features including mild ptosis, thick upper lip, and prominent nose were noted that had not been observed previously. Neurologic examination revealed a moderate cerebellar syndrome, including intention tremor of arms, moderate gait ataxia, and nystagmus. The intrinsic hand muscles were paretic, resulting in disabling flexion contractures of both hands. Mild bilateral weakness of the anterior tibial muscle (MRC grade 4/5) was noted. There was no weakness of the proximal arm and leg muscles. A bilateral distal decrease of both touch and vibration sense (3/8 at the toes) of the lower extremities was noted. Tendon reflexes were absent. Results of the neurophysiologic examination had not changed since age 12 years. Sensory nerve potentials were unobtainable. Peroneal motor NCV were not measurable with surface electrodes because of complete denervation of the extensor digitorum brevis muscle. Ulnar motor NCV was 28 m/s, distal latency was 4.5 ms, CMAP was 0.1 mV. Median motor NCV were not measurable because of complete denervation of the thenar muscles. Electromyography of the intrinsic hand muscles revealed chronic neurogenic changes.
Patient 4.
Clinical and electrophysiologic findings at age 4 years were published previously.12 In total, the girl has had three episodes of acute weakness of both legs and arms and elevated serum CK after febrile infections. Symptoms resolved within 4 weeks to 3 months.
When the girl was reexamined at age 11, dysmetria of both arms, intention tremor, moderate gait ataxia, and nystagmus were noted. There was no sensory deficit. There was a severe paresis of the intrinsic foot musculature with a pes equinovarus deformity and a slight paresis of the intrinsic hand muscles. Tendon reflexes were absent. Neurophysiologic examination showed absent sensory action potentials in the median, ulnar, radial, and sural nerves. Peroneal motor NCV was 12 m/s, distal latency was 6.4 ms, and the CMAP was 0.2 mV. Ulnar motor NCV was 26 m/s, distal latency was 4.3 ms, and the CMAP was 0.2 mV. The median motor NCV was unobtainable. Electromyographic examination, performed in this patient before the first episode of acute myalgia and myoglobinuria, showed a neurogenic pattern.12
Patients 5 and 6.
Patients 5 and 6 (patients S.K. and S.M in Müller-Felber et al.12) are the first and second children of healthy, nonconsanguineous Gypsy parents who immigrated to Germany from two different towns in southern Serbia. They were diagnosed with MSS and recurrent myoglobinuria.
Patient 5.
The clinical and electrophysiologic findings of this child at age 7 are described in our original publication.12 By age 16, the girl had a history of two episodes of acute weakness and elevated CK after febrile infections. The intervals between onset of weakness and recovery were 3 weeks and 3 months. Furthermore, there was steady progression of a distal and symmetric polyneuropathy leading to equinovarus deformity of both feet. She had myalgia after prolonged exercise. For longer distances, she used a wheelchair. She also reported repeated ankle fractures and weight gain during the last 3 years.
Upon examination at age 16, the patient showed distinctive facial features, ptosis, short stature, and obesity (see figure 2). Neurologic examination revealed moderate cerebellar syndrome, including gait ataxia and nystagmus. Intrinsic hand muscles were mildly paretic (MRC grade 4/5). Mild bilateral weakness of the anterior tibial muscle (MRC grade 4/5) was noted. There was no weakness of proximal arm and leg muscles. Touch and vibration sense of the lower extremities were normal. Tendon reflexes were absent. The results of the neurophysiologic examination had slightly deteriorated since age 7 years. However, sensory NCV remained better than motor NCV. Median nerve motor conduction velocity was decreased to 23 m/s, distal latency was 4.3 ms, and CMAP was 1 mV. Peroneal motor NCV was unobtainable. Sensory nerve potential of the median nerve was 36 m/s, and sensory nerve action potential was 6 μV. Sural nerve conduction velocity was not obtainable. Electromyographic examination revealed spontaneous activity in the right thenar muscle, chronic neurogenic changes with long-duration, and high-amplitude motor unit action potentials in the thenar and tibialis anterior muscles.
Patient 6.
Clinical and electrophysiologic findings at age 4 years were published previously.12 The boy repeatedly had severe myalgia during febrile infections. However, he did not experience prolonged episodes of muscle weakness after these infections. He also had myalgia after prolonged exercise. Furthermore, distal and symmetric polyneuropathy steadily progressed, leading to mild equinovarus deformity of both feet. In general, he was less severely affected than his older sister.
When the boy was reexamined at age 14, mild facial abnormalities and slight bilateral ptosis were noted (see figure 2). He showed moderate gait ataxia and mildly paretic intrinsic hand and anterior tibialis muscles (MRC grade 4/5). There was no weakness of proximal arm and leg muscles. Touch and vibration sense of the lower extremities were normal. Tendon reflexes were absent. The results of the neurophysiologic examination had slightly deteriorated since age 4 years. However, sensory NCV remained better than motor NCV. Median motor nerve was 26 m/s, distal latency was 3.6 ms, CMAP was 1.5 mV. Peroneal motor NCV was 22 m/s, distal latency was 5.5 ms, and CMAP was 0.5 mV. Sensory nerve potential of the median nerve was 35 m/s, and amplitude was 6 μV; the sural nerve sensory nerve potential was 35 m/s, and amplitude was 5 μV. Electromyographic examination of the biceps muscle showed normal features; chronic neurogenic changes were detected in the tibialis anterior muscles.
Genetic analysis.
The families with MSS were genotyped for six microsatellite markers on 18q23-qter. Figures 1 and 3⇓ show the results. Multipoint linkage analysis produced a combined maximum lod score of 3.55 at marker 1908ca1.
Figure 3. Polymorphic haplotypes in the 18qter region in 86 CCFDN chromosomes11 (Gooding and Kalaydjieve, 2000, unpublished data) (upper part of the figure) and the MSS chromosomes analyzed in this study. In addition to the highly conserved haplotype, the two groups of chromosomes share identical recombinant haplotypes (shaded in gray) that are likely to result from the same recombination events. CCFDN = congenital cataracts facial dysmorphism neuropathy; MSS = Marinesco–Sjögren syndrome.
The analysis of MSS haplotypes revealed that they are closely related to the conserved haplotype found in CCFDN chromosomes (see figure 3). Patients 5 and 6 displayed the conserved CCFDN haplotype over the entire region, and Patients 1 and 2 showed conserved halotype over most of the region (see figures 1 and 3⇑). Patients 3 and 4 presented with historical recombinations, both centromeric and telomeric, that appeared identical to those observed previously in Bulgarian Gypsy CCFDN chromosomes (see figures 1 and 3⇑). In addition, a paternal recombination was observed in Patient 3 involving marker D18S70, and possibly the next centromeric marker, D18S1390 (see figures 1 and 3⇑). All six patients were homozygous for the conserved alleles of markers 1908ca1 and D18S1095, identical to all 86 CCFDN chromosomes studied so far (see figure 3).
Discussion.
We have identified a third family, of Italian Gypsy origin, with the subtype of MSS described previously in Gypsy patients in Germany.12 The clinical picture includes cataracts recognized in the first month of life, developmental delay, small stature, skeletal deformities, cerebellar dysfunction with ataxia, nystagmus, intention tremor and dysmetria, mild mental retardation, peripheral neuropathy, and recurrent episodes of acute parainfectious myalgia, profound weakness, marked CK elevation, and myoglobinuria. Although CMAP values were mildly to moderately reduced in our patients, a primarily demyelinating nature of the peripheral neuropathy is suggested by the consistently observed severe slowing of nerve conduction velocities to less than 70% of the lower normal limit. The affected families are not related to one another, suggesting that this MSS subtype may be relatively common in Gypsies.
Episodes of parainfectious myalgia with myoglobinuria were recorded in five of our patients. Their absence, so far, in one of the affected subjects could be because of the partly environmental nature of this manifestation, in which specific viral infections may be required to act as a trigger. In the general population, severe myoglobinuria is a rare complication of viral infection.14 Its familial nature and cosegregation with the other manifestations indicates that it is part of the clinical phenotype of the MSS subtype we are studying.
Myoglobinuria is often associated with metabolic myopathies such as McArdle syndrome, phosphofructokinase deficiency, carnitine palmitoyltransferase deficiency, and mitochondrial disorders (COX deficiency, cytochrome b deficiency, coenzyme Q10 deficiency).15 Its occurrence in MSS could add further support to a previously proposed hypothesis that MSS is a metabolic disorder.4,6,16-18⇓⇓⇓⇓ Muscle biopsy specimens of two patients, one of which was already reported,12 showed normal histochemical reactions including myophosphorylase and phosphofructokinase activities, and no mitochondrial proliferation or ragged-red fibers, thus excluding the major cause of rhabdomyolysis related to metabolic myopathies. Neither of these patients had a history of myoglobinuria precipitated by exercise, cold, or fasting, thus making carnitine palmitoyltransferase deficiency unlikely. Although the cause and mechanisms remain to be clarified, recurrent attacks of myoglobinuria may occasionally lead to acute renal failure. A patient with this MSS subtype developed anesthesia-induced malignant hyperthermia during cataract surgery.19 These rare but life-threatening complications must be considered when treating Gypsy patients with MSS.
MSS has substantial clinical heterogeneity even with regard to its cardinal features. Cataracts can be congenital7,12,17-18,20-21⇓⇓⇓⇓⇓ or may develop at a later age with a variable rate of progression.3,16,22-25⇓⇓⇓⇓⇓ Cerebellar involvement is a prerequisite for the diagnosis and has been reported in all cases; however, there is marked variation in its severity, as well as in the underlying morphologic changes in the central nervous system. Neuroimaging findings range from severe cerebellar atrophy,3,5,16,24-26⇓⇓⇓⇓⇓ supported by autopsy findings27-29⇓⇓ to diffuse brain atrophy with or without minimal evidence of cerebellar involvement.17,20,30,31⇓⇓⇓ Similarly, intellectual development can vary between mild retardation12,16,18,20,25,31,32⇓⇓⇓⇓⇓⇓ and severe impairment.8,19,21,24,26⇓⇓⇓⇓ Neuromuscular manifestations may be absent1,21,22,30,33⇓⇓⇓⇓ or may include myopathy,3-6,16,23,24,32,34⇓⇓⇓⇓⇓⇓⇓⇓ demyelinating7,8,18,19⇓⇓⇓ or axonal26,31⇓ neuropathy, or both myopathy and neuropathy.12,20⇓ The ultrastructural observations of a dense membranous structure associated with nuclei in some muscle biopsy specimens4,32⇓ have not been replicated in other studies.3,6,12,35⇓⇓⇓
The closest phenotypic similarity to CCFDN is in MSS cases with documented very early onset cataracts, developmental delay, mild-to-moderate intellectual deficit, mild to moderate cerebellar dysfunction, and peripheral neuropathy. This phenotype can be regarded as atypical MSS, because in the family described by Marinesco,1 cataract development occurred after age 1 year and peripheral nerve involvement was absent. Differential diagnosis between the above subtype of MSS and CCFDN syndrome appears to depend on two features. Cerebellar dysfunction is mandatory for MSS diagnosis, whereas it is very mild and inconsistent in CCFDN. Only 20% of patients with CCFDN had cerebellar symptoms, but none of the 16 examined by MRI showed any evidence of cerebellar atrophy.10 The second distinctive clinical feature is facial dysmorphism.10 With one exception,17 distinctive facial features are not mentioned in the published descriptions of individuals with MSS, and it is unclear whether the patients with MSS of mixed Irish/Sicilian descent reported by Walker et al.17 resemble in appearance the CCFDN patients. Facial dysmorphism in CCFDN develops gradually and is more pronounced in men.10 In the group of patients in which CCFDN was initially characterized, facial dysmorphism was noted in about 60% of children under age 15 and in 87% of women.10
Families included in our study generally have this MSS subtype, with acute recurrent myoglobinuria as a specific additional characteristic. Cerebellar dysfunction was present in all patients. Neuroimaging studies revealed cerebellar atrophy in two cases,12 whereas MRI scan results were normal in Patient 1 at age 6 years. Distinctive facial features were not noted at the initial examination of our four original patients,12 but are becoming apparent as the disease progresses, especially in the older Patients 3 and 5. Comparison with CCFDN subjects shows a similarity that may increase with age.10
The patients affected by MSS with demyelinating neuropathy and recurrent myoglobinuria are Gypsies, and thus originate from the same genetically isolated founder population as individuals with CCFDN syndrome.10 This prompted us to conduct linkage and haplotype analyses of markers located in the 18qter region, where the CCFDN gene is located.11 Linkage analysis produced a lod score of 3.55, thus confirming colocalization of the gene responsible for MSS, with demyelinating neuropathy and myoglobinuria, with the CCFDN gene. All MSS chromosomes carried closely related marker haplotypes in the 18q region despite the fact that the affected families are not related and originate from different parts of Europe. The MSS haplotype was identical to the conserved haplotype defined by the study of CCFDN patients.11 The sharing of an identical segment on chromosome 18qter, inherited from a distant common ancestor, suggests that MSS and CCFDN chromosomes carry the same founder mutation that causes the two disorders.
The genetic basis of other subtypes of MSS remains to be determined. The presence of acute myopathy in our patients indicates that the CCFDN/atypical MSS gene may be expressed in muscle. Moreover, differences in the muscle and cerebellar involvement suggest a phenotypic variation within the same genetic entity. Locus heterogeneity and locus homogeneity in the MSS appear equally plausible and equally intriguing in terms of future genotype–phenotype correlations.
Acknowledgments
Supported by the Wellcome Trust, Edith Cowan University, and the Australian Research Council. H.L. is supported by grants from the Deutsche Forschungsgemeinschaft and the Duchenne Parents Project of Germany.
Footnotes
-
L.M. and R.G. contributed equally to this work.
- Received July 6, 2001.
- Accepted September 29, 2001.
References
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