MED12-Related (Neuro)Developmental Disorders: A Question of Causality

MED12 is a member of the Mediator complex that is involved in the regulation of transcription. Missense variants in MED12 cause FG syndrome, Lujan-Fryns syndrome, and Ohdo syndrome, as well as non-syndromic intellectual disability (ID) in hemizygous males. Recently, female patients with de novo missense variants and de novo protein truncating variants in MED12 were described, resulting in a clinical spectrum centered around ID and Hardikar syndrome without ID. The missense variants are found throughout MED12, whether they are inherited in hemizygous males or de novo in females. They can result in syndromic or nonsyndromic ID. The de novo nonsense variants resulting in Hardikar syndrome that is characterized by facial clefting, pigmentary retinopathy, biliary anomalies, and intestinal malrotation, are found more N-terminally, whereas the more C-terminally positioned variants are de novo protein truncating variants that cause a severe, syndromic phenotype consisting of ID, facial dysmorphism, short stature, skeletal abnormalities, feeding difficulties, and variable other abnormalities. This broad range of distinct phenotypes calls for a method to distinguish between pathogenic and non-pathogenic variants in MED12. We propose an isogenic iNeuron model to establish the unique gene expression patterns that are associated with the specific MED12 variants. The discovery of these patterns would help in future diagnostics and determine the causality of the MED12 variants.

Neonatal hypotonia and neuromuscular conditions

The differential diagnosis of neonatal hypotonia is a complex task, as in newborns hypotonia can be the presenting sign of different underlying causes, including peripheral and central nervous system involvement and genetic and metabolic diseases. This chapter describes how a combined approach, based on the combination of clinical signs and new genetic techniques, can help not only to establish when the hypotonia is related to peripheral involvement but also to achieve an accurate and early diagnosis of the specific neuromuscular diseases with neonatal onset. The early identification of such disorders is important, as this allows early intervention with disease-specific standards of care and, more importantly, because of the possibility to treat some of them, such as spinal muscular atrophy, with therapeutic approaches that have recently become available.

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.

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.

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.

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.

Retrograde lacrimal duct airflow during nasal positive pressure ventilation

Noninvasive ventilation is widely used for chronic respiratory failure in children with neuromuscular disorders, thus avoiding the need for tracheostomy. However, the pressures required to support ventilation in these children may be considerably higher than those necessary to treat obstructive sleep apnea. The complications of nasal positive airway pressure are numerous, including skin breakdown, conjunctivitis, nasal congestion, airway dryness, pneumothorax, and bowel obstruction. Ophthalmologic complaints are particularly common, largely attributed to an air leak in the mask. In the present case, we demonstrate, through two modalities-video and CT scan-retrograde airflow through the nasolacrimal duct causing sleep disruption and eye irritation in a profoundly hypotonic 14-month-old boy with chronic respiratory failure on bilevel ventilation during sleep.

Branching enzyme deficiency/glycogenosis storage disease type IV presenting as a severe congenital hypotonia: muscle biopsy and autopsy findings, biochemical and molecular genetic studies

The fatal infantile neuromuscular presentation of branching enzyme deficiency (glycogen storage disease type IV) due to mutations in the gene encoding the glycogen branching enzyme, is a rare but probably underdiagnosed cause of congenital hypotonia. We report an infant girl with severe generalized hypotonia, born at 33 weeks gestation who required ventilatory assistance since birth. She had bilateral ptosis, mild knee and foot contractures and echocardiographic evidence of cardiomyopathy. A muscle biopsy at 1 month of age showed typical polyglucosan storage. The autopsy at 3.5 months of age showed frontal cortex polymicrogyria and polyglucosan bodies in neurons of basal ganglia, thalamus, substantia innominata, brain stem, and myenteric plexus, as well as liver involvement. Glycogen branching enzyme activity in muscle was virtually undetectable. Sequencing of the GBE1 gene revealed a homozygous 28 base pair deletion and a single base insertion at the same site in exon 5. This case confirms previous observations that GBE deficiency ought to be included in the differential diagnosis of congenital hypotonia and that the phenotype correlates with the 'molecular severity' of the mutation.

[Nemaline myopathy as a cause of neonatal hypotonia - with emphasis on personal experiences. Report of a family with two brothers affected]

Nemaline myopathy is a heterogenous form of congenital myopathy characterised by a variable spectrum of clinical features, predominated in the severe form by profound muscle hypotonia and weakness accompanied by respiratory insufficiency. The clinical variability, with differing age of onset and severity of symptoms makes the diagnosis of nemaline myopathy difficult in some cases. Severe forms of nemaline myopathy may be caused by mutation of a number of different genes: skeletal muscle actin (ACTA1), nebulin (NEB) and alpha-tropomyosin (TPM3), all of which encode components of the sarcomeric thin filaments of skeletal muscle. We describe the severe form of nemaline myopathy diagnosed in two brothers who died at the age of 12 days and 9 months, due to respiratory insufficiency caused by severe muscle weakness. Polyhydramnios and weakness of foetal movements in the IIIrd trimester of pregnancy, as well as variable clinical severity were noted in both cases. Microscopically visible significant immaturity of muscle fibers was found in the skeletal muscle biopsy performed in one of the brothers. The diagnosis of nemaline myopathy was confirmed by the presence of nemaline bodies (rods) in sections stained using the Gomori trichrome method. Molecular studies of DNA isolated from blood leucocytes showed no mutation in the ACTA1 or the TPM3 genes. Linkage analysis with polymorphic markers did not rule out linkage to part of the NEB gene locus. Results of the clinical evaluation and the investigations performed in the family members confirm that it is essential to consider congenital myopathies in the differential diagnosis of neonatal and infantile hypotonia with respiratory insufficiency. Molecular verification of the clinical diagnosis is also important for genetic counselling of the families.

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.

[Cap myopathy: a case report]

AIM

To report a new case of a little-known congenital myopathy. Cap myopathy is a rare congenital disease caused by an alteration in the structure of the fibre, with disorganised myofibrils at the edges. Since it was first described, only a few cases have been reported in the literature.

CASE REPORT

We describe the case of a 16-year-old patient with a history of neonatal hypotonia and psychomotor retardation. At the age of 4 years, the patient presented myopathic facies with atrophied pectoral muscles, winged scapula and lumbar hyperlordosis. A myopathic pattern was observed in the electromyogram. A muscle biopsy showed a very marked predominance of type I fibres, atrophy in part of the population of this type and 20% of them had cap-shaped subsarcolemmal accumulations, which were intensely positive with DPNH and SDH; in the ultrastructural study they correspond to disorganised peripheral myofibrils with preservation of the Z band and the absence of A bands. These alterations are similar to those described in what is known as cap disease or cap myopathy. Today, the patient has mild proximal tetraparesis and moderate restrictive respiratory failure.

Congenital cataracts facial dysmorphism neuropathy (CCFDN) syndrome: a rare cause of parainfectious rhabdomyolysis

Congenital cataracts-facial dysmorphism-neuropathy syndrome (CCFDN, MIM: 604168), is a recently delineated neurogenetic disease causing recurrent episodes of rhabdomyolysis; prevention and early diagnosis of rhabdomyolysis should be part of the clinical management of the disease.

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.

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.

[Gillespie syndrome: an uncommon presentation of congenital aniridia]

We report here the case of a patient suffering from Gillespie syndrome (GS) (partial aniridia, mental retardation, and cerebellar ataxia). The typical presentation is based on fixed dilated pupils in a hypotonic child. Iris abnormalities distinguish GS from other forms of aniridia. At the time of initial presentation, neurological involvement and radiologic abnormalities could be absent or delayed. Genetic determinism is still unknown. The pattern of inheritance seems to be heterogeneous, according to the autosomal recessive and autosomal dominant forms previously described.

Basicranial diplomyelia: an extension of the split cord malformation theory. Case report

Basicranial diastematomyelia is an extremely rare congenital disorder. A review of the literature indicates only one reported case of basicranial diastematomyelia in which an osseous peg divided the brainstem in two. The authors present the first reported case of basicranial diplomyelia split by a fibrous band and correlate its pathogenesis with that of split cord malformation (SCM). The patient described in the present report had a fibrous stalk dividing the brainstem, and therefore the condition was categorized as a diplomyelia, or SCM Type II. Because the occipital dermatomes behave similarly to the spinal dermatomes early in development, they may be subject to the same embryonic error that results in SCM. The authors propose that the mechanism leading to SCM is the same as that found in basicranial split malformations and that the theory explaining it be modified to include the posterior fossa.

Pallister-Killian syndrome (PKS): clinical case report

Pallister-Killian Syndrome is a rare dysmorphic condition characterized by specific clinical manifestations and tetrasomy 12p. This paper focuses on the general and orofacial clinical manifestations.

[Congenital myotonic dystrophy--the significance of a handshake]

Three neonates, all girls, were presented immediately after birth with severe hypotonia. Two of them needed artificial ventilation because of respiratory insufficiency. All three pregnancies had been complicated by reduced fetal movements and moderate cerebral ventricular dilatation and in two of the three there was also polyhydramnios and congenital talipes. In all three infants congenital myotonic dystrophy was suspected after diagnosing myotonia in the mother. This was done by observing that none of the mothers were unable to release their grip immediately on command after shaking hands. Ophthalmological examination of the women revealed polychromatic lens crystals characteristic of myotonic dystrophy. Congenital myotonic dystrophy was confirmed by DNA analysis, as well as myotonic dystrophy in the mothers. All had an expansion of the number of cytosine-thymine-guanine(CTG)-trinucleotides in a part of the myotonic dystrophy protein-kinase gene. The first two infants died after 2 days and 15 months respectively.

[LAMB2 gene mutation as a cause of congenital nephrotic syndrome with distinct eye abnormalities and hypotonia]

Mutations in the LAMB2 gene encoding laminin beta2, a component of the glomerular basement membrane and the neuro-muscular junction are responsible for the characteristic renal and eye abnormalities of Pierson syndrome. We report a girl with confirmed LAMB2 mutation who presented with early onset Congenital Nephrotic Syndrome (CNS) with renal failure and ocular findings of bilateral microcoria, persistent hyperplastic primary vitreous, right microphtalmia and left eye cataract. Automated peritoneal dialysis was started from the 3rd month of life. Severe muscle hypotonia with motor and mental delay were observed during the first year of life. She experienced numerous serious infections from birth and died at the age of 15 months due to a fulminant infection. Genetic studies revealed two novel mutations in LAMB2 gene (compound heterozygosity).

CONCLUSIONS

1. Mutations in LAMB2 gene should be included in the work-up of patients with CNS in the presence of eye anomalies. 2. Severe phenotypes of Pierson syndrome are associated with marked handicaps and a poor outcome.

Clinical and histologic changes in the follow-up of a congenital myopathy

A 19-year-old woman was born with congenital hypotonia, generalized weakness, and dysmorphic features. A muscle biopsy performed at age 18 months found that type I fibers were smaller and more numerous than type II fibers, and she was diagnosed with congenital fiber type disproportion. She grew up with moderate motor impairment, but after a stationary period her weakness progressed gradually and she developed a severe ophthalmoplegia. When she was 18 years old a second muscle biopsy still indicated the predominance of type I fibers but also the presence of central nuclei and strong oxidative enzyme activity in the center of most of the fibers; this was compatible with centronuclear myopathy. The diagnostic reconsideration raises questions about the pathogenesis of these diseases and the recognition of congenital fiber type disproportion as a distinct nosologic entity.

A new syndrome of myopathy with muscle spindle excess

Arthrogryposis may result from various neuromuscular or connective tissue disorders leading to in utero hypokinesia or akinesia and the prenatal development of joint contractures. We report the case of a preterm neonate born with arthrogryposis and flaccid quadriplegia that led to the diagnosis of myopathy with muscle spindle excess. The rare and unusual histopathologic abnormality associated with the myopathy illustrated in this case has been described in only three other cases in the medical literature. The concurrence of hypertrophic cardiomyopathy, arthrogryposis, and myopathy with muscle spindle excess suggests the presence of a newly described syndrome. This case clearly demonstrates that specific prenatal ultrasonographic findings combined with the presenting clinical manifestations should promptly raise the suspicion of a neuromuscular disorder.

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.

A new case of Okamoto syndrome

We report a 6 month old boy with congenital hydronephrosis, cleft palate, severe hypotonia, congenital heart defect, developmental delay, and characteristic facial features with an open mouthed appearance and full lower lip, who we believe is the third reported case of Okamoto syndrome. Okamoto syndrome is a recently described distinctive multiple congenital anomaly syndrome encompassing the above features for which an etiologic factor has not yet been identified. Our patient also had idiopathic splenomegaly and non-specific MRI changes in the brain, not reported in the first two cases.

Midbrain disconnection: an aetiology of severe central neonatal hypotonia

A full term girl exhibited massive hypotonia related to severe posterior fossa abnormalities consisting of pontocerebellar hypoplasia with midbrain disconnection. The latter was due to lack of one and marked hypoplasia of the other cerebral peduncles. In addition, there was mild vermian and cerebellar hypoplasia. Compared to usual pontocerebellar hypoplasia, the midbrain disconnection is a distinctive feature of our case. It is a rare malformation only three similar cases have previously been described.

A novel MPZ gene mutation in congenital neuropathy with hypomyelination

Congenital hypomyelinating neuropathy (CHN; MIM# 605253) is a severe neuropathy with early infancy onset inherited as an autosomal dominant or recessive trait. Sural nerve biopsy shows a characteristic picture of nonmyelinated and poorly myelinated axons with basal lamina onion bulbs and lack of myelin breakdown products. Several mutations in the MTMR2, PMP22, EGR2, and MPZ genes have been found in patients with CHN. The authors describe the clinical and morphologic features of a patient with CHN and the identification of a novel Thr124Lys mutation in the MPZ gene.

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.

POMGnT1 gene alterations in a family with neurological abnormalities

Muscle-eye-brain disease (MEB), is caused by mutations in the POMGnT1 gene. We describe a white family with two siblings affected with congenital hypotonia early-onset glaucoma, and psychomotor delays. Brain magnetic resonance images (MRIs) showed hydrocephalus, bilateral frontal polymicrogyria, abnormal cerebellum, and characteristic flattened dystrophic pons. We identified novel POMGnT1 gene alterations in this family. Both affected siblings were found to be compound hetrozygotes and carried two missense changes inherited from their mother and one missense change (p.R442C) inherited from their father. Our findings further define the phenotypic spectrum of MEB and its occurrence in the US population.

The myopathology of floppy and hypotonic infants in Singapore

AIMS

This study attempts to determine the type and relative frequency of muscle diseases contributing to floppy and hypotonic infants in Singapore.

METHODS

Eighty consecutive muscle biopsies in the Department of Pathology, National University of Singapore, in the period 1978-2000, in which a clinical diagnosis of floppy or hypotonic infant was made, were reviewed.

RESULTS

The commonest cause of severe hypotonia in infancy was spinal muscular atrophy, which accounted for 33% of cases followed by congenital muscular dystrophy (13%). Eight cases (10%) of infantile type II glycogenosis (Pompe's disease) were encountered. There were seven cases of congenital myopathy, of which four were centronuclear myopathy, and one each of central core myopathy, nemaline myopathy and congenital fibre type disproportion. One case of centronuclear myopathy was associated with type I fibre smallness. Type II atrophy, which is generally considered a non-specific change, was encountered in five cases. Of interest is the relatively large number of muscle biopsies (29%) in which no significant pathological features were encountered at the light microscopic, histochemical as well as ultra-structural level.

CONCLUSIONS

The study has revealed a great variety of pathology affecting the muscle of children presenting as floppy infants or with hypotonia. The muscle diseases included spinal muscular atrophy, congenital muscular dystrophies, congenital myopathies and metabolic myopathies. However, 23 (29%) cases showed no significant pathology. For this group of floppy and hypotonic infants further studies are needed.

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.

Brainstem dysgenesis: report of five patients with congenital hypotonia, multiple cranial nerve involvement, and ocular motor apraxia

This paper reports three females and two males with a distinctive congenital syndrome characterized by severe congenital hypotonia, facial diplegia, jaw ankylosis, velo-pharyngeal incoordination, pyramidal tract signs, and ocular motor apraxia. Patients were followed up at ages ranging from 20 months to 16 years. All cases of this syndrome are sporadic, without dysmorphological features, chromosomal, or MRI brain abnormalities. Electrophysiological studies indicate the brainstem as the site of the neurological dysfunction. Post-mortem CNS study of one of the patients demonstrated neuronal depletion of the IV, VII, VIII, and IX cranial nerve nuclei and intact morphology of the cerebral hemispheres. A vascular accident, early in foetal life, is the most likely cause of the clinical picture. The extent of brainstem involvement and its related clinical findings distinguishes these patients from those with Moebius, Pierre Robin, or Cogan syndromes. Outcome is better than what could be anticipated during the first few months of life given the severity of symptoms. Intelligence or developmental quotients are within the normal range for their age. Facial hypomimia, feeding, and speech articulatory performance difficulties are the main disabilities observed in these patients at follow-up.

Congenital hypotonia with favorable outcome

Congenital hypotonia with favorable outcome is characterized by an early neonatal onset and a benign clinical course. The old term, proposed by Walton, was benign congenital hypotonia, denoting the presence of muscle weakness and hypotonia, with the exception of Werdnig-Hoffmann disease. It has been clear that this term includes congenital myopathies with definite changes in the muscle fiber. However, many cases remain unclarified. The term congenital hypotonia with favorable outcome includes only these last cases. A long-term follow-up study of children with congenital hypotonia with favorable outcome is presented, and a hypothetical mechanism underlying muscle shortening is discussed. The study was carried out at the Department of Child Neuropsychiatric Sciences, University "La Sapienza" of Rome, during the period 1985-2000, and included 41 patients with congenital hypotonia. Our study confirms the good prognosis of congenital hypotonia with favorable outcome and suggests a correlation with joint hyperlaxity, which is observed in many parents of our children, as if the latter developed from the former. On the basis of experimental changes occurring in the muscles, we believe that in our cohort the main cause of shortening is caused by an increase in joint mobility, which keeps muscles shortened in both the passive and active states for a long time. If this view is confirmed by other studies, we suggest continuous muscle exercise as a preventive treatment.

Congenital cervical spinal atrophy: an intrauterine hypoxic insult

We present two patients with congenital cervical spinal atrophy who were born at 37 and 33 weeks of gestation. Both patients were unrelated and had no family history of neuromuscular diseases. They presented at birth with arthrogryposis multiplex and symmetrical severe muscle weakness and wasting confined to the upper extremities. There was no sensory or bulbar symptom. Electromyography showed polyphasic and fast-firing units in the proximal muscles of the upper extremities. With the evidence of chronic denervation and re-innervation, we speculate that this static condition is most likely due to circulatory insufficiency causing anterior horn cell ischemia during the latter part of the first trimester.

Congenital hypomyelination neuropathy in a newborn infant: unusual cause of diaphragmatic and vocal cord paralyses

We report a case of congenital hypomyelination neuropathy presenting at birth. The infant had generalized hypotonia and weakness. There was decreased respiratory effort along with a right phrenic nerve and left vocal cord paralyses. Tongue fasciculations were present. Deep tendon reflexes were absent in the upper extremities and hypoactive (1+) in the lower extremities. Magnetic resonance imaging of the head revealed no intracranial abnormalities, including normal cerebral myelination. Nerve conduction study showed absence of motor and sensory action potentials in the hands when the nerves in the upper limbs were stimulated. A motor response could be elicited only in the proximal leg muscles. Needle electromyography study was normal in the proximal limb muscles, but showed active denervation in the distal muscles of the arm and leg. These findings were thought to be consistent with a length-dependent sensorimotor peripheral polyneuropathy of axonal type with greater denervation of the distal muscles. A biopsy of the quadriceps muscle showed mild variability in fiber diameter, but no group typing or group atrophy. The muscle fibers showed no intrinsic abnormalities. Biopsy of the sural nerve showed scattered axons with very thin myelin sheaths. There was also a nearly complete loss of large diameter myelinated fibers. No onion bulb formations were noted. These findings were thought to be consistent with congenital hypomyelination neuropathy with a component of axonopathy. DNA analysis for identification of previously characterized mutations in the genes MPZ, PMP22, and EGR2 was negative. Several attempts at extubation failed and the infant became increasingly ventilator-dependent with increasing episodes of desaturation and hypercapnea. He also developed increasing weakness and decreased movement of all extremities. He underwent surgery at 2 months of age for placement of a gastrostomy tube and a tracheostomy. He was discharged from the hospital on a ventilator at 6 months of age. The infant was 13 months old at the time of submission of this report. Although he appears cognitively normal, he remains profoundly hypotonic and is on a home ventilator. There was no evidence of progressive weakness. Congenital hypomyelination neuropathy is a rare form of neonatal neuropathy that should be considered in the differential diagnosis of a newborn with profound hypotonia and weakness. It appears to be a heterogeneous disorder with some of the cases being caused by specific genetic mutations.

Absence of correlation between infantile hypotonia and foramen magnum size in achondroplasia

Virtually all infants with achondroplasia exhibit variably severe hypotonia in infancy. This hypotonia contributes to delays in motor development and risks for sudden death. Some have proposed that this hypotonia is a direct result of impaired function of long tracts of the spinal cord, secondary to the intrinsic narrowing of the foramen magnum, which also is present in variable severity in all children with achondroplasia. We postulated that if foraminal constriction causes infantile hypotonia, then there should be a strongly positive correlation between foraminal size and severity of hypotonia. Therefore, clinical and computed tomographic data in 71 infants were retrospectively reviewed. We found no correlation. These results suggest that there is no direct relationship and foraminal size does not affect severity of hypotonia. Other potential explanations for this infantile hypotonia are considered.

[Neonatal hypotonia of muscular origin: analysis of 50 cases]

BACKGROUND

Neonatal hypotonia is a common request for neurological consultation. The aim of this study is to describe the main clinical features of muscular hypotonia in newborns at the light of the histopathological findings.

METHODS

We reviewed 50 medical records of hypotonic neonates with abnormal muscular biopsy. In all of the cases, the serum concentration of creatine kinase was determined and biopsies were examined by a qualified neuropathologist.

RESULTS

The most frequent muscular cause of neonatal hypotonia was specific congenital myopathies (23 cases), followed by congenital muscular dystrophy (15 cases), congenital myotonic dystrophy (eight cases) and metabolic myopathies (four cases). The most common specific congenital myopathy was fiber type disproportion (10 cases). The association with joint contractures and the involvement of respiratory muscles were frequent; respiratory complications were the first cause of death.

CONCLUSIONS

Muscular biopsy is required for the definitive diagnosis of specific congenital myopathies, congenital muscular dystrophy and metabolic myopathies. In congenital myotonic dystrophy, the mother is almost always affected; neonates with specific congenital myopathies and congenital muscular dystrophy can be very similar to those with congenital myotonic dystrophy; the examination of the mother, specially a careful search for myotonia, is the best diagnostic clue; if there are signs of myotonia, the diagnosis can be made by molecular genetic study.

Question mark ears, temporo-mandibular joint malformation and hypotonia: auriculo-condylar syndrome or a distinct entity?

We report a boy with prominent, peculiarly malformed ears, abnormality of the ramus of the mandible and hypotonia. An isolated peculiar bilateral ear deformity named 'question mark ear' has been delineated in plastic reconstruction surgery reviews [Cosman et al., 1970 Plast Reconstr Surg 46:454-457; Cosman (1984) Plast Reconstr Surg 73:572-576; Takato et al. (1989) Ann Plast Surg 22:69-73; Brodovsky (1997) Plast Reconstr Surg 100:1254-1257; Park (1998) Plast Reconstr Surg 101:1620-1623; Al-Quattan (1998) Plast Reconstr Surg 102:439-441] and a similar deformity of the ear and changes in the temporo-mandibular joint and condyle has been described by Jampol et al. [(1998) Am J Med Genet 75:449-452] and by Guion-Almeida et al. [(1999) Am J Med Genet 86:130-133]. The present case may be the third description of this malformation complex with additional clinical features characterized by hypotonia and mild developmental delay, or possibly a new distinct entity.

[Congenital hernia of the diaphragm. A retrospective study of 123 cases recorded in the Neonatal Medicine Department, URHC in Lille between 1985 and 1996]

BACKGROUND

During the last ten years, new therapeutic strategies have been used in order to improve the management of congenital diaphragmatic hernia (CDH). CDH is associated with pulmonary hypoplasia, abnormal pulmonary vascular reactivity and pulmonary immaturity. Between 1985 and 1990, mechanical hyperventilation and early surgery were provided systematically. Since 1991, the management of CDH in our institution has involved a preoperative stabilization with exogenous surfactant replacement, gentle ventilation, high-frequency oscillation, nitric oxide or extracorporeal membrane oxygenation.

PURPOSE

To analyse the impact of the new therapeutic strategy on the survival and outcome of newborns with CDH.

METHODS

Retrospective review of all infants with CDH admitted to our institution from 1985 through 1996. Mortality and morbidity were compared between period I (1985-1990) and period II (1991-1996).

RESULTS

Between 1985 and 1996, 123 neonates were admitted to our Neonatal Department. Nine of them had another severe congenital malformation and were excluded from the study. Survival was 23% (12/52) in period I and 56% (35/62) in period II (p < 0.001). In period II, complications were more frequent among survivors in whom an extracorporeal membrane oxygenation was required (13 infants): bronchopulmonary dysplasia 77% (10/13), gastroesophageal reflux 61% (8/13), and hypotrophy 61% (8/13).

CONCLUSION

These data demonstrate a significant improvement in survival in CDH since the implementation of new therapeutic modalities. Nevertheless, a significant morbidity exists among the infants who survive a severe respiratory failure.

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.

[Smith-Lemli-Opitz syndrome]

BACKGROUND

Smith-Lemli-Opitz syndrome (SLOS) is an autosomic recessive metabolic affection. Children affected by SLOS exhibit a defect in cholesterol biosynthesis associated with a high concentration of cholesterol precursor 7 dehydrocholesterol (7 DHC) and its isomers, which is due to an enzymatic block at the level of delta-7-DHC reductase. SLOS has been subdivided into two types on the basis of clinical severity: type I is the classic and type II is the severe one.

CASE REPORT

A full term female was born from a pregnancy complicated by oligoamniosis and intra-uterine growth retardation. The neurologic status was immediately impaired with severe hypotonia, absence of reflexes, and abnormal crying. She exhibited multiple congenital anomalies with a facial dysmorphia, anomalies of members, unicornus uterus and a pyloric stenosis. Plasmatic concentration exhibited a normal cholesterolemia contrasting with an elevated level of 7 and 8 DHC. Major alimentary tract defect led to enteral and parenteral nutrition. The severe neurological defect led to death on the 16th day of life.

CONCLUSION

Despite normal blood cholesterol levels that can be attributed to enteral and parenteral nutrition, the severity of clinical findings and the lethal course permit to classify this case as type II.

Evidence for a new X-linked mental retardation gene in Xp21-Xp22: clinical and molecular data in one family

Linkage analysis was performed in three generations of a French family segregating a syndromal form of X-linked mental retardation. All affected males had neonatal hypotonia, seizures, muscular hypodevelopment, and severe mental deficiency. A peak lod score of 2.90 at a recombination fraction of theta = 0 was detected for DXS 1052 and DXS 451 (Xp22.13). Recombination between the disease locus and the polymorphic markers in DXS7163 and DXS1238 suggested a gene mapping to the Xp22.13-Xp21.2 region. Three candidate genes in this region were investigated: the cDNA for kinase Rsk-2 involved in Coffin-Lowry syndrome, the brain-specific exon of a transcript in the DMD locus (DP140 isoform of dystrophin), and exon 18 of the glycerol kinase gene, which is specific to fetal brain transcripts. All three sequences were normal.

Developmental correlates of school-age children with a history of benign congenital hypotonia

In order to clarify the prognosis of benign congenital hypotonia (BCH), 25 children aged 6 to 8 years who had been diagnosed with BCH as infants were examined on a variety of sensory, perceptual-motor, and behavioural measures and compared with 26 control children. There were no significant differences between the two groups on any of the medical or neurological measures of the Touwen Neurological Examination (Touwen 1979), nor were there significant overall differences on any of the sensory or behavioural measures. However, the BCH group showed inferior gross motor performance on the Bruininks-Oseretsky Test of Motor Proficiency (Bruininks 1978). They scored significantly lower on the Gross Motor Composite, and performed worse on each of the four Gross Motor Subtests, reaching significance on two: Bilateral Coordination and Strength. The follow-up of children with BCH should continue even after the apparent resolution of the hypotonia, with particular attention to the gross motor aspects of performance.

A gene for FG syndrome maps in the Xq12-q21.31 region

FG syndrome is an X-linked recessive condition in which mental retardation is associated with congenital hypotonia, macrocephaly, characteristic face, and constipation. This syndrome was mapped by Zhu et al. [Cytogenet Cell Genet 1991;58:2091A] to Xq21.31-q22 by linkage analysis with a max lod score of 1.2 for the DXYS1X, DXS178, DXS101, and DXS94 loci and crossovers at DXS16 (Xp22.31) and DXS287 (Xq22.3). However, this mapping was only provisional and needed to be refined. In this paper, we report the results of a new linkage analysis performed on 10 families including that studied by Zhu et al. [1991]. Two-point analysis demonstrated linkage with DXS441 (Zmax = 3.39 at theta = 0.12) at Xq13. In addition, separate analysis of the lod scores obtained for the Xq13 markers suggested linkage exclusion for three families. Genetic heterogeneity was confirmed by analysis of the linkage results with the HOMOG program (max logL = 4.07, theta = 0, alpha = 0.65). Localization of one FG gene between DXS135 and DXS1066 was suggested by analysis of crossovers found in those three families which were assumed to be linked to Xq13 with a probability of 0.95 or more. This region could be reduced to the DXS135-DXS72 interval after combining our data with those from deletions previously described in males in the Xq13-q21 region.

Congenital familial myopathy with type 2 fiber hypoplasia and type 1 fiber predominance

A 12-month-old girl with delayed developmental milestones, due to muscle hypotonia and weakness from early infancy, exhibited type 2 fiber hypoplasia. A muscle biopsy specimen disclosed type 1 fiber predominance and type 2B fiber deficiency compatible with congenital myopathy. During the following 4 years, she continued to have mild muscle weakness, but no mental retardation. Her mother had similar symptoms from early infancy with minimal progression. Although type 2 fiber hypoplasia is a non-specific finding in various diseases, it may be a specific finding in a limited number of patients with hereditary congenital non-progressive myopathy.