Congenital Fiber Type Disproportion—30 Years On

Thirty years ago, M. H. Brooke coined the term "congenital fiber type disproportion" (CFTD) to describe 12 children who had clinical features of a congenital myopathy and relative type 1 fiber hypotrophy on muscle biopsy. It is now clear that this histological pattern can accompany a wide range of neurological disorders, leading to disillusionment with CFTD as a distinct nosological entity. To determine whether the CFTD has clinical utility as a diagnostic entity, we have reviewed the literature for cases of type 1 fiber hypotrophy and have used strict exclusion criteria to identify 67 cases of CFTD. Most patients presented at birth with weakness and hypotonia, had normal intelligence, and followed a static or improving clinical course. In 43% of families, more than 1 individual was affected. Failure to thrive was common and 25% of patients had contractures or spinal deformities. Bulbar weakness and ophthalmoplegia were less common and cardiac involvement was rare. Twenty-five percent followed a severe course and 10% had died at the time of reporting, all from respiratory failure. Ophthalmoplegia and facial and bulbar weakness were significantly associated with a poorer prognosis. The relatively homogeneous phenotype supports the retention of CFTD as a distinct diagnostic entity and familial occurrence suggests a genetic basis. Regarding the diagnosis of CFTD, we found no strong evidence that the minimum difference between type 1 and type 2 fiber sizes should be increased from 12% to 25%. We also list the other reported causes of relative type 1 fiber hypotrophy to aid their exclusion from CFTD.

Dominant ER Stress-Inducing WFS1 Mutations Underlie a Genetic Syndrome of Neonatal/Infancy-Onset Diabetes, Congenital Sensorineural Deafness, and Congenital Cataracts

Neonatal diabetes is frequently part of a complex syndrome with extrapancreatic features: 18 genes causing syndromic neonatal diabetes have been identified to date. There are still patients with neonatal diabetes who have novel genetic syndromes. We performed exome sequencing in a patient and his unrelated, unaffected parents to identify the genetic etiology of a syndrome characterized by neonatal diabetes, sensorineural deafness, and congenital cataracts. Further testing was performed in 311 patients with diabetes diagnosed before 1 year of age in whom all known genetic causes had been excluded. We identified 5 patients, including the initial case, with three heterozygous missense mutations in WFS1 (4/5 confirmed de novo). They had diabetes diagnosed before 12 months (2 before 6 months) (5/5), sensorineural deafness diagnosed soon after birth (5/5), congenital cataracts (4/5), and hypotonia (4/5). In vitro studies showed that these WFS1 mutations are functionally different from the known recessive Wolfram syndrome-causing mutations, as they tend to aggregate and induce robust endoplasmic reticulum stress. Our results establish specific dominant WFS1 mutations as a cause of a novel syndrome including neonatal/infancy-onset diabetes, congenital cataracts, and sensorineural deafness. This syndrome has a discrete pathophysiology and differs genetically and clinically from recessive Wolfram syndrome.

Human cerebellar hypoplasia: a syndrome of diverse causes

Seven children had congenitally small cerebella. Perinatal asphyxia was not a factor. Clinical signs in infancy were generalized muscular hypotonia, delayed development, truncal titubation, and intention tremor. Most had fixation nystagmus and esotropia. Three had seizures and an abnormal EEG. Pneumoencephalography in each case revealed a small cerebellum with prominent folia, large fourth ventricle, wide vallecula, large cisterna magna, and normal lateral and third ventricles. A computerized tomography scan in one case showed similar findings. One patient had an absent corpus callosum. One patient died at 2 1/2 years. The cerebellar hemispheres and vermis were small. Granular cells were absent throughout. Purkinje's cells were preserved, but had dendritic swellings with radiating fibrils. Cerebellar, pontine, and inferior olivary nuclei showed mild neuronal loss. The clinical and pathologic findings resemble those of animal models of cerebellar hypoplasia produced by fetal exposure to certain viruses, toxins, or repeated low doses of radiation. Cerebellar hypoplasia is a clinical syndrome of several causes, but with many symptoms and signs in common.

Beta1 integrins in muscle, but not in motor neurons, are required for skeletal muscle innervation

In vitro studies have provided evidence that beta1 integrins in motor neurons promote neurite outgrowth, whereas beta1 integrins in myotubes regulate acetylcholine receptor (AChR) clustering. Surprisingly, using genetic studies in mice, we show here that motor axon outgrowth and neuromuscular junction (NMJ) formation in large part are unaffected when the integrin beta1 gene (Itgb1) is inactivated in motor neurons. In the absence of Itgb1 expression in skeletal muscle, interactions between motor neurons and muscle are defective, preventing normal presynaptic differentiation. Motor neurons fail to terminate their growth at the muscle midline, branch excessively, and develop abnormal nerve terminals. These defects resemble the phenotype of agrin-null mice, suggesting that signaling molecules such as agrin, which coordinate presynaptic and postsynaptic differentiation, are not presented properly to nerve terminals. We conclude that Itgb1 expression in muscle, but not in motor neurons, is critical for NMJ development.

Biallelic IARS Mutations Cause Growth Retardation with Prenatal Onset, Intellectual Disability, Muscular Hypotonia, and Infantile Hepatopathy

tRNA synthetase deficiencies are a growing group of genetic diseases associated with tissue-specific, mostly neurological, phenotypes. In cattle, cytosolic isoleucyl-tRNA synthetase (IARS) missense mutations cause hereditary weak calf syndrome. Exome sequencing in three unrelated individuals with severe prenatal-onset growth retardation, intellectual disability, and muscular hypotonia revealed biallelic mutations in IARS. Studies in yeast confirmed the pathogenicity of identified mutations. Two of the individuals had infantile hepatopathy with fibrosis and steatosis, leading in one to liver failure in the course of infections. Zinc deficiency was present in all affected individuals and supplementation with zinc showed a beneficial effect on growth in one.

Congenital hypotonia revisited

The definition of neuromuscular diseases affecting infants has depended on factors as various as the rate of progression of the illness, the clinical picture, and, recently, the morphologic peculiarities in the muscle biopsy. A review of the literature suggests that there are discrepancies in the classification of such illnesses, no matter what system is used. In some instances, a single diagnosis seems to include patients with quite separate illnesses, whereas other patients with seemingly identical diseases have been given different diagnoses.

βIV Spectrinopathies Cause Profound Intellectual Disability, Congenital Hypotonia, and Motor Axonal Neuropathy

βIV spectrin links ankyrinG (AnkG) and clustered ion channels at axon initial segments (AISs) and nodes of Ranvier to the axonal cytoskeleton. Here, we report bi-allelic pathogenic SPTBN4 variants (three homozygous and two compound heterozygous) that cause a severe neurological syndrome that includes congenital hypotonia, intellectual disability, and motor axonal and auditory neuropathy. We introduced these variants into βIV spectrin, expressed these in neurons, and found that 5/7 were loss-of-function variants disrupting AIS localization or abolishing phosphoinositide binding. Nerve biopsies from an individual with a loss-of-function variant had reduced nodal Na+ channels and no nodal KCNQ2 K+ channels. Modeling the disease in mice revealed that although ankyrinR (AnkR) and βI spectrin can cluster Na+ channels and partially compensate for the loss of AnkG and βIV spectrin at nodes of Ranvier, AnkR and βI spectrin cannot cluster KCNQ2- and KCNQ3-subunit-containing K+ channels. Our findings define a class of spectrinopathies and reveal the molecular pathologies causing nervous-system dysfunction.

Neurodevelopmental deficits in Pierson (microcoria-congenital nephrosis) syndrome

Pierson syndrome is an autosomal recessive disorder comprising congenital nephrotic syndrome with diffuse mesangial sclerosis and distinct eye abnormalities with microcoria reported as the most prominent clinical feature. LAMB2 mutations leading to lack of laminin beta2 were identified as the molecular cause underlying Pierson syndrome. Although LAMB2 is known to be expressed in the neuromuscular system, and defects of the neuromuscular junctions had been found in laminin beta2-deficient mice, no consistent neurological phenotype has been described clinically in murine or human laminin beta2-deficiency before. This is likely due to the early lethality from renal failure. Here we provide a detailed description of neurological manifestations and development in four patients affected by Pierson syndrome, who survived until the age of 1.3-4.8 years owing to renal replacement therapy. Severe muscular hypotonia, psychomotor retardation, and blindness were present in three patients harboring truncating mutations on both LAMB2 alleles. These symptoms were not attributable to complications of chronic renal failure, thus representing a primary feature of the genetic disorder. Alterations in skeletal muscle tissue from one case were compatible with a chronic denervating process. One affected girl, however, exhibited a milder course of renal disease, normal development, and preserved vision, presumably owing to some residual LAMB2 function. Our findings indicate that severe neurodevelopmental deficits have to be considered as part of Pierson syndrome, at least in the presence of biallelic functional null mutations (complete lack of laminin beta2). This is an important issue in the counseling of parents of an affected newborn or infant.

Congenital hypotonia: is there an algorithm?

This study was performed with the aim of determining the diagnostic profile of newborns with hypotonia and of analyzing the usefulness of different procedures in the diagnostic process. One hundred thirty-eight hypotonic newborns were identified through the search of hospital records in a 10-year period: 121 (88%) had central hypotonia and 13 (9%) had peripheral hypotonia, whereas 4 (3%) remained unclassified. Analysis of the contribution of clinical data and results of investigations led to the construction of an algorithm, by which all cases in the group were diagnosed. Step 1, which included clinical data and results of examinations, solved 50% of all diagnosed cases. Neuroimaging techniques made up step 2 and contributed to the diagnosis in 13%. Step 3 was accomplished by a search through Oxford Medical Databases, which yielded the final diagnosis in 9%, whereas karyotyping and fluorescent in situ hybridization for Prader-Willi syndrome comprised step 4 and contributed to the diagnosis in 6.5%. Biochemical tests formed step 5 and contributed to the diagnosis in 6%. Step 6, which included specific investigations of muscle and nerve, was diagnostic in 6%. The remaining cases (6.5%) were diagnosed only after several follow-up examinations. These results could assist the neonatologist when deciding the diagnostic approach to floppy newborns.

Congenital hypomyelinating neuropathy

Two patients with congenital hypomyelinating neuropathy are reported with details of sural nerve pathology. The resemblance of this condition to the hypomyelinating neuropathy of Trembler mice is discussed and the pertinent medical literature reviewed.

Congenital fibre type disproportion myopathy. A histological diagnosis with an uncertain clinical outlook

Nine children with congenital fibre type disproportion (CFTD) are described. Their muscle biopsies contained type 1 fibres which were smaller than the largest type 2 fibres by at least 13.5%. Attention is drawn to the variable natural history of this disorder which generally carries a good prognosis but may sometimes be associated with fatal respiratory problems. For important therapeutic, genetic, and prognostic reasons CFTD must be distinguished from other conditions with similar histochemical or clinical features.

Clinical, morphological, biochemical, imaging and outcome parameters in 21 individuals with mitochondrial maintenance defect related to FBXL4 mutations

FBXL4 deficiency is a recently described disorder of mitochondrial maintenance associated with a loss of mitochondrial DNA in cells. To date, the genetic diagnosis of FBXL4 deficiency has been established in 28 individuals. This paper retrospectively reviews proxy-reported clinical and biochemical findings and evaluates brain imaging, morphological and genetic data in 21 of those patients. Neonatal/early-onset severe lactic acidosis, muscular hypotonia, feeding problems and failure to thrive is the characteristic pattern at first presentation. Facial dysmorphic features are present in 67% of cases. Seven children died (mean age 37 months); 11 children were alive (mean age at follow-up 46 months), three children were lost to follow-up. All survivors developed severe psychomotor retardation. Brain imaging was non-specific in neonates but a later-onset, rapidly progressive brain atrophy was noted. Elevated blood lactate and metabolic acidosis were observed in all individuals; creatine kinase was elevated in 45% of measurements. Diagnostic workup in patient tissues and cells revealed a severe combined respiratory chain defect with a general decrease of enzymes associated with mitochondrial energy metabolism and a relative depletion of mitochondrial DNA content. Mutations were detected throughout the FBXL4 gene albeit with no clear delineation of a genotype-phenotype correlation. Treatment with "mitochondrial medications" did not prove effective. In conclusion, a clinical pattern of early-onset encephalopathy, persistent lactic acidosis, profound muscular hypotonia and typical facial dysmorphism should prompt initiation of molecular genetic analysis of FBXL4. Establishment of the diagnosis permits genetic counselling, prevents patients undergoing unhelpful diagnostic procedures and allows for accurate prognosis.

Global distribution of the most prevalent deletions causing hypotonia-cystinuria syndrome

Hypotonia-cystinuria syndrome (HCS) is a recessive disorder caused by microdeletions of SLC3A1 and PREPL on chromosome 2p21. Patients present with generalized hypotonia at birth, failure to thrive, growth retardation and cystinuria type I. While the initially described HCS families live in small regions in Belgium and France, we have now identified HCS alleles in patients and carriers from the Netherlands, Italy, Canada and United States of America. Surprisingly, among the nine deletions detected in those patients, only one novel deletion was found. Furthermore, one previously described deletion was found six times, another twice. Finally, we have investigated the frequency of both deletions using a random Belgian cohort. Given the global occurrence, HCS should be considered in the differential diagnosis of neonatal hypotonia.

Type 1 fiber size disproportion: morphometric data from 37 children with myopathic, neuropathic, or idiopathic hypotonia

We reviewed clinical data and quantitative muscle biopsy data from infants with hypotonia and developmental delay who had relatively small type 1 muscle fibers (fiber size disproportion; FSD). Study material consisted of 49 thigh muscle specimens from 37 patients, 1 week to 11.5 years old, who had FSD diagnosed between 1971 and 1985. Beyond 2 months of age, FSD was greater than 12% in at least one biopsy from all but 2 patients. In sequential specimens obtained from 11 patients, we observed that FSD may resolve, persist unchanged, or intensify with age. In 6 patients, hypotonia regressed, and development tended to normalize during 1-4 years of observation; FSD resolved in 4 cases, but numerical predominance of type 1 fibers persisted in 3 of them. In a small group designated congenital myopathy with FSD only, the disproportion in fiber diameter persisted unchanged or intensified with time and was more severe after the age of 6 months than in the other subgroups. We classified FSD as definitely or probably myopathic (15 cases), definitely or probably neuropathic (17 cases), and benign maturation delay (5 cases). Six of 17 neuropathic cases had a history of perinatal asphyxia. In most cases, type 1 fibers were absolutely small and type 2 fibers were hypertrophied, independent of classification. FSD is a manifestation of muscle maturation delay of variable etiology. The prevalence of nervous system disorders in our series suggests that neuronal dysfunction plays an important role in pathogenesis. We were unable to define morphometric criteria that consistently distinguished congenital myopathy with FSD from definable neuropathic FSD or from benign maturation delay.

A milder variant of Pierson syndrome

Congenital nephrotic syndrome (CNS) comprises a heterogeneous group of conditions having in common the disruption of normal glomerular permselectivity, and it carries a poor prognosis, with most patients progressing to end-stage renal disease. Recently, mutations in the LAMB2 gene encoding laminin beta2 were described as the cause of Pierson syndrome, which is characterized by CNS and a complex ocular maldevelopment with microcoria as the most prominent clinical features. Most affected children exhibit early onset of chronic renal failure, neurodevelopmental deficits, and blindness. We report on a patient with CNS, high-grade myopia, and minor structural eye anomalies, including remnants of pupillary membranes, but no microcoria. The patient had not developed renal failure by the age of 16 months, and he showed no neurodevelopmental deficits. He was identified to be homozygous for a novel LAMB2 missense mutation. This observation, together with two recent reports on milder variants of Pierson syndrome, corroborates the concept that the clinical expression of Pierson syndrome is more variable than initially described, and that milder phenotypes may be related to hypomorphic LAMB2 alleles.

The FG syndrome: 7 new cases

The X-linked FG syndrome is characterised by mental retardation, congenital hypotonia and constipation (which may both be severe), structural anal anomalies and relative macrocephaly in some, and an unusual and characteristic facial appearance. We describe 7 males from 4 families. One had anal stenosis. Two of the mothers and one sister show probable carrier manifestations. The features of the FG syndrome are individually non-specific. We emphasize that the characteristic combination of features is needed to avoid overdiagnosis.

Clinical variability in congenital fiber type disproportion

Congenital Fiber Type Disproportion (CFTD) has recently been described as a consistent and stereotyped clinicopathological entity, including congenital nonprogressive hypotonia and weakness, contractures, kyphoscoliosis, high arched palate, dislocated hips, short stature, and feet deformities. Our personal experience with this condition suggests a wider disparity in the physical appearance and associated abnormalities of affected individuals than the well-defined clinical syndrome previously described. We are presenting 5 cases, including 2 siblings, whose muscle biopsies satisfy the major histological and statistical criteria for the diagnosis. Although each child clearly had hypotonia and weakness consistent with a congenital myopathy, only 3 had a sufficient number of other similarities to establish the diagnosis clinically. The clinical spectrum of the other cases ranged from one infant whose only abnormality was mild hypotonia in the legs to another whose problems included severe motor impairment, marked mental retardation, growth failure, frontal bossing, abnormal hair, and scoliosis. Even in retrospect, the diagnosis of CFTD could not have been supported on clinical grounds alone. Therefore, CFTD is a congenital myopathy whose diagnosis can be made only by muscle biopsy, rather than a distinct syndrome whose diagnosis can be assumed on the basis of clinical characteristics alone.

Congenital inflammatory myopathy

We present 3 patients with congenital inflammatory myopathy and summarize the literature. CNS involvement (microcephaly/intellectual delay) may or may not be present. Serum creatine kinase activity is elevated, the EMG is myopathic, and the muscle biopsy reveals inflammatory infiltrates, muscle fiber damage, and class I major histocompatibility complex products in muscle sarcolemma. Possible etiologies include intrauterine viral infection or an autoimmune process. Treatment with steroids may result in some motor improvement but has no effect on the CNS involvement. Despite a common time of presentation, these patients have a heterogeneous clinical profile, often suggesting a congenital muscular dystrophy syndrome.

Patterns of muscle fiber-type disproportion in hypotonic infants

We studied the histochemical characteristics of muscle in five hypotonic infants. A number of different patterns of disproportion in the sizes and numbers of type 1 and type 2 fibers were found. In three cases, type 1 fibers were smaller than type 2 fibers and type 2b or 2c fibers were largest. In one case, type 2 fibers were smaller than type 1 fibers and were reduced in number, while in a case of Prader-Willi syndrome there was a preponderance of type 2 fibers that were smaller than type 1 fibers. Type 2c fibers were increased in number in all but one case. We postulate that these various patterns of fiber-type disproportion are the result of altered neural influences leading to impaired maturation of type 1 or type 2 motor units.

Brief clinical report and review: the Marden-Walker syndrome

We have studied a sibship with one confirmed and three probable cases of the Marden-Walker syndrome (MWS). Our patient had the major manifestations of blepharophimosis and squint; narrowly arched palate with micrognathia; small mouth and mouth-breathing; facial deformities and distortions; congenital muscle weakness with resulting scoliosis; mild pectus excavatum; camptodactylies and hip and finger joints subluxation. In addition, he had small, apparently low-set and slightly malformed auricles with a unilateral preauricular tag. However, he had no apparent renal or cardiovascular involvement. Results of CPK, EMG, and of histochemical, light microscopic, and ultrastructural studies of muscle biopsy do not suggest a primary myopathy but rather CNS related weakness/hypotonia with small muscle mass and hypoactive DTRs. This pathogenetic hypothesis is confirmed by the presence of severe mental retardation and minor brain changes suggesting cortical atrophy. In five previously reported cases there has been microcephaly. Phenotype analysis does not convince that the MWS is a true malformation syndrome, but rather hints at the possibility of a congenital metabolic dysplasia. Genetic analysis demonstrated autosomal-recessive inheritance in this and two other instances; primarily sporadic occurrence leaves open the possibility of genetic heterogeneity.

New XLMR syndrome with characteristic face, hypogenitalism, congenital hypotonia and pachygyria

A previously unreported X-linked MCA/MR syndrome is described in 4 members of a large family. Phenotypic manifestations include mental retardation, microcephaly, failure to thrive, severe congenital hypotonia, characteristic face, hypogenitalism, pachygyria. This appears to be an X-linked dominant trait with decreased penetrance and expressivity in carrier females.

Congenital fiber type disproportion in identical twins

Eighteen-month-old identical twins with the muscle histological characteristics of congenital fiber type disproportion are reported. The fiber typing system of pH-dependent adenosine triphosphatase was used to analyze the size and percentage of type 1, 2A, and 2B fibers in muscle tissue obtained by needle biopsy. Both twins had significantly larger type 2 than type 1 fibers, with 2B fibers representing the largest type. One patient also had type 1 predominance at the expense of a reduction in 2B (2B deficiency). The probands as well as other family members had transient delayed motor development, macrocephaly, and normal intelligence. A biopsy obtained from 1 of these family members failed to demonstrate a similar histological abnormality. The disorder is nonprogressive in this family, as evidenced by minimal disability in the older members and gradual improvement in the probands.

Blaschkolinear malformation syndrome in complex trisomy-7 mosaicism

Results of repeated peripheral blood chromosome studies were normal in a boy with intrauterine growth retardation, short stature, moderate mental retardation, and multiple minor anomalies. At age 9 years it was recognized that the swirls of pigmentation/depigmentation on his trunk, linear streaks on his limbs, and body asymmetry were suggestive of chromosomal mosaicism. Four skin biopsies were obtained under anesthesia during a dental procedure. All showed mosaicism for a normal cell line, a line with an extra chromosome 7, and a cell line with an extra small ring. In one biopsy, there was a fourth cell line with an extra chromosome 7 and the ring. Fluorescence in situ hybridization (FISH) with a chromosome 7 paint confirmed trisomy 7 and the chromosome 7 derivation of the ring. This young man's intra-uterine and postnatal growth retardation is an aneuploidy effect, whereas his asymmetry reflects a mosaicism effect that should have aroused suspicion of tissue-limited mosaicism before the development of obvious Blaschkolinear skin pigmentary dysplasia.