Molecular characterization of 13 patients with PIK3CA-related overgrowth spectrum using a targeted deep sequencing approach

Activating variants in the PIK3CA gene cause a heterogeneous spectrum of disorders that involve congenital or early-onset segmental/focal overgrowth, now referred to as PIK3CA-related overgrowth spectrum (PROS). Historically, the clinical diagnoses of patients with PROS included a range of distinct syndromes, including CLOVES syndrome, dysplastic megalencephaly, hemimegalencephaly, focal cortical dysplasia, Klippel-Trenaunay syndrome, CLAPO syndrome, fibroadipose hyperplasia or overgrowth, hemihyperplasia multiple lipomatosis, and megalencephaly capillary malformation-polymicrogyria (MCAP) syndrome. MCAP is a sporadic overgrowth disorder that exhibits core features of progressive megalencephaly, vascular malformations, distal limb malformations, cortical brain malformations, and connective tissue dysplasia. In 2012, our research group contributed to the identification of predominantly mosaic, gain-of-function variants in PIK3CA as an underlying genetic cause of the syndrome. Mosaic variants are technically more difficult to detect and require implementation of more sensitive sequencing technologies and less stringent variant calling algorithms. In this study, we demonstrated the utility of deep sequencing using the Illumina TruSight Oncology 500 (TSO500) sequencing panel in identifying variants with low allele fractions in a series of patients with PROS and suspected mosaicism: pathogenic, mosaic PIK3CA variants were identified in all 13 individuals, including 6 positive controls. This study highlights the importance of screening for low-level mosaic variants in PROS patients. The use of targeted panels with deep sequencing in clinical genetic testing laboratories would improve diagnostic yield and accuracy within this patient population.

Autoantibodies against type I IFNs in humans with alternative NF-κB pathway deficiency

Patients with autoimmune polyendocrinopathy syndrome type 1 (APS-1) caused by autosomal recessive AIRE deficiency produce autoantibodies that neutralize type I interferons (IFNs)1,2, conferring a predisposition to life-threatening COVID-19 pneumonia3. Here we report that patients with autosomal recessive NIK or RELB deficiency, or a specific type of autosomal-dominant NF-κB2 deficiency, also have neutralizing autoantibodies against type I IFNs and are at higher risk of getting life-threatening COVID-19 pneumonia. In patients with autosomal-dominant NF-κB2 deficiency, these autoantibodies are found only in individuals who are heterozygous for variants associated with both transcription (p52 activity) loss of function (LOF) due to impaired p100 processing to generate p52, and regulatory (IκBδ activity) gain of function (GOF) due to the accumulation of unprocessed p100, therefore increasing the inhibitory activity of IκBδ (hereafter, p52LOF/IκBδGOF). By contrast, neutralizing autoantibodies against type I IFNs are not found in individuals who are heterozygous for NFKB2 variants causing haploinsufficiency of p100 and p52 (hereafter, p52LOF/IκBδLOF) or gain-of-function of p52 (hereafter, p52GOF/IκBδLOF). In contrast to patients with APS-1, patients with disorders of NIK, RELB or NF-κB2 have very few tissue-specific autoantibodies. However, their thymuses have an abnormal structure, with few AIRE-expressing medullary thymic epithelial cells. Human inborn errors of the alternative NF-κB pathway impair the development of AIRE-expressing medullary thymic epithelial cells, thereby underlying the production of autoantibodies against type I IFNs and predisposition to viral diseases.

Compound heterozygous variants in SHQ1 are associated with a spectrum of neurological features, including early-onset dystonia

SHQ1 is essential for biogenesis of H/ACA ribonucleoproteins, a class of molecules important for processing ribosomal RNAs, modifying spliceosomal small nuclear RNAs, and stabilizing telomerase. Components of the H/ACA ribonucleoprotein complex have been linked to neurological developmental defects. Here we report two sibling pairs from unrelated families with compound heterozygous variants in SHQ1. Exome sequencing was used to detect disease causing variants which were submitted to 'matching' platforms linked to MatchMaker Exchange. Phenotype comparisons supported these matches. The affected individuals present with early-onset dystonia, with individuals from one family displaying additional neurological phenotypes, including neurodegeneration. As a result of CSF studies suggesting possible abnormal dopamine metabolism, a trial of levodopa replacement therapy was started but no clear response was noted. We show that fibroblasts from affected individuals have dramatic loss of SHQ1 protein. Variants from both families were expressed in S. cerevisiae, resulting in a strong reduction in H/ACA snoRNA production and remarkable defects in rRNA processing and ribosome formation. Our study identifies SHQ1 as associated with neurological disease, including early-onset dystonia, and begins to delineate the molecular etiology of this novel condition.

Loss of function mutations in GEMIN5 cause a neurodevelopmental disorder

GEMIN5, an RNA-binding protein is essential for assembly of the survival motor neuron (SMN) protein complex and facilitates the formation of small nuclear ribonucleoproteins (snRNPs), the building blocks of spliceosomes. Here, we have identified 30 affected individuals from 22 unrelated families presenting with developmental delay, hypotonia, and cerebellar ataxia harboring biallelic variants in the GEMIN5 gene. Mutations in GEMIN5 perturb the subcellular distribution, stability, and expression of GEMIN5 protein and its interacting partners in patient iPSC-derived neurons, suggesting a potential loss-of-function mechanism. GEMIN5 mutations result in disruption of snRNP complex assembly formation in patient iPSC neurons. Furthermore, knock down of rigor mortis, the fly homolog of human GEMIN5, leads to developmental defects, motor dysfunction, and a reduced lifespan. Interestingly, we observed that GEMIN5 variants disrupt a distinct set of transcripts and pathways as compared to SMA patient neurons, suggesting different molecular pathomechanisms. These findings collectively provide evidence that pathogenic variants in GEMIN5 perturb physiological functions and result in a neurodevelopmental delay and ataxia syndrome.

Multisystem inflammation and susceptibility to viral infections in human ZNFX1 deficiency

BACKGROUND

Recognition of viral nucleic acids is one of the primary triggers for a type I interferon-mediated antiviral immune response. Inborn errors of type I interferon immunity can be associated with increased inflammation and/or increased susceptibility to viral infections as a result of dysbalanced interferon production. NFX1-type zinc finger-containing 1 (ZNFX1) is an interferon-stimulated double-stranded RNA sensor that restricts the replication of RNA viruses in mice. The role of ZNFX1 in the human immune response is not known.

OBJECTIVE

We studied 15 patients from 8 families with an autosomal recessive immunodeficiency characterized by severe infections by both RNA and DNA viruses and virally triggered inflammatory episodes with hemophagocytic lymphohistiocytosis-like disease, early-onset seizures, and renal and lung disease.

METHODS

Whole exome sequencing was performed on 13 patients from 8 families. We investigated the transcriptome, posttranscriptional regulation of interferon-stimulated genes (ISGs) and predisposition to viral infections in primary cells from patients and controls stimulated with synthetic double-stranded nucleic acids.

RESULTS

Deleterious homozygous and compound heterozygous ZNFX1 variants were identified in all 13 patients. Stimulation of patient-derived primary cells with synthetic double-stranded nucleic acids was associated with a deregulated pattern of expression of ISGs and alterations in the half-life of the mRNA of ISGs and also associated with poorer clearance of viral infections by monocytes.

CONCLUSION

ZNFX1 is an important regulator of the response to double-stranded nucleic acids stimuli following viral infections. ZNFX1 deficiency predisposes to severe viral infections and a multisystem inflammatory disease.

Heterozygous intragenic deletions of FREM1 are not associated with trigonocephaly

Recessive mutations in FRAS1-related extracellular matrix 1 (FREM1) are associated with two rare genetic disorders, Manitoba-oculo-tricho-anal (MOTA) and bifid nose with or without anorectal and renal anomalies (BNAR). Fraser syndrome is a more severe disorder that shows phenotypic overlap with both MOTA and anorectal and renal anomalies and results from mutations in FRAS1, FREM2 and GRIP1. Heterozygous missense mutations in FREM1 were reported in association with isolated trigonocephaly with dominant inheritance and incomplete penetrance. Moreover, large deletions encompassing FREM1 have been reported in association with a syndromic form of trigonocephaly and were designated as trigonocephaly type 2. Trigonocephaly results from premature closure of the metopic suture and typically manifests as a form of nonsyndromic craniosynostosis. We report on 20 patients evaluated for developmental delay and without abnormal metopic suture. Chromosomal microarray analysis revealed heterozygous FREM1 deletions in 18 patients and in 4 phenotypically normal parents. Two patients were diagnosed with MOTA and had homozygous FREM1 deletions. Therefore, although our results are consistent with the previous reports of homozygous deletions causing MOTA, we report no association between heterozygous FREM1 deletions and trigonocephaly in this cohort.

The Canadian Rare Diseases Models and Mechanisms (RDMM) Network: Connecting Understudied Genes to Model Organisms

Advances in genomics have transformed our ability to identify the genetic causes of rare diseases (RDs), yet we have a limited understanding of the mechanistic roles of most genes in health and disease. When a novel RD gene is first discovered, there is minimal insight into its biological function, the pathogenic mechanisms of disease-causing variants, and how therapy might be approached. To address this gap, the Canadian Rare Diseases Models and Mechanisms (RDMM) Network was established to connect clinicians discovering new disease genes with Canadian scientists able to study equivalent genes and pathways in model organisms (MOs). The Network is built around a registry of more than 500 Canadian MO scientists, representing expertise for over 7,500 human genes. RDMM uses a committee process to identify and evaluate clinician-MO scientist collaborations and approve 25,000 Canadian dollars in catalyst funding. To date, we have made 85 clinician-MO scientist connections and funded 105 projects. These collaborations help confirm variant pathogenicity and unravel the molecular mechanisms of RD, and also test novel therapies and lead to long-term collaborations. To expand the impact and reach of this model, we made the RDMM Registry open-source, portable, and customizable, and we freely share our committee structures and processes. We are currently working with emerging networks in Europe, Australia, and Japan to link international RDMM networks and registries and enable matches across borders. We will continue to create meaningful collaborations, generate knowledge, and advance RD research locally and globally for the benefit of patients and families living with RD.

Characterization of a Unique Form of Arrhythmic Cardiomyopathy Caused by Recessive Mutation in LEMD2

Nuclear envelope proteins have been shown to play an important role in the pathogenesis of inherited dilated cardiomyopathy. Here, we present a remarkable cardiac phenotype caused by a homozygous LEMD2 mutation in patients of the Hutterite population with juvenile cataract. Mutation carriers develop arrhythmic cardiomyopathy with mild impairment of left ventricular systolic function but severe ventricular arrhythmias leading to sudden cardiac death. Affected cardiac tissue from a deceased patient and fibroblasts exhibit elongated nuclei with abnormal condensed heterochromatin at the periphery. The patient fibroblasts demonstrate cellular senescence and reduced proliferation capacity, which may suggest an involvement of LEM domain containing protein 2 in chromatin remodeling processes and premature aging.

A homozygous canonical splice acceptor site mutation in PRUNE1 is responsible for a rare childhood neurodegenerative disease in Manitoba Cree families

Autosomal recessive PRUNE1 mutations are reported to cause a severe neurodevelopmental disorder with microcephaly, hypotonia, and brain malformations. We describe clinical and neuropathological features in a cohort of nine individuals of Cree descent who, because of a founder effect, are homozygous for the same PRUNE1 mutation. They follow the course of a combined neuromuscular and neurodegenerative disease, rather than a pure failure of normal development. This cohort presented in infancy with features of lower motor neuron disease, such as hypotonia, contractures, tongue fasciculations, and feeding difficulties in the absence of congenital brain anomalies and microcephaly. A neurodegenerative course followed with onset of seizures, spasticity, and respiratory insufficiency. Muscle biopsies showed denervation/reinnervation features, nonspecific atrophy and end-stage atrophy. Autopsy findings in two patients are also described, suggesting length dependent central motor axon degeneration, peripheral motor axon degeneration, possible spinal motor neuron degeneration, and accumulation of beta amyloid precursor protein inclusions in select brainstem nuclei. Exome sequencing and homozygosity mapping identified a homozygous PRUNE1 mutation in a canonical splice site, which produces two abnormal PRUNE1 mRNA products. Based on our studies and the histopathology and phenotypic data, we provide further evidence that this disorder leads to a neurodegenerative disease affecting both the peripheral and central nervous systems and suggest that the pathogenic c.521-2A>G mutation could lead to an altered effect on tubulin dynamics.

A truncating mutation in CEP55 is the likely cause of MARCH, a novel syndrome affecting neuronal mitosis

Background

Hydranencephaly is a congenital anomaly leading to replacement of the cerebral hemispheres with a fluid-filled cyst. The goals of this work are to describe a novel autosomal-recessive syndrome that includes hydranencephaly (multinucleated neurons, anhydramnios, renal dysplasia, cerebellar hypoplasia and hydranencephaly (MARCH)); to identify its genetic cause(s) and to provide functional insight into pathomechanism.

Methods

We used homozygosity mapping and exome sequencing to identify recessive mutations in a single family with three affected fetuses. Immunohistochemistry, RT-PCR and imaging in cell lines, and zebrafish models, were used to explore the function of the gene and the effect of the mutation.

Results

We identified a homozygous nonsense mutation in CEP55 segregating with MARCH. Testing the effect of this allele on patient-derived cells indicated both a reduction of the overall CEP55 message and the production of a message that likely gives rise to a truncated protein. Suppression or ablation of cep55l in zebrafish embryos recapitulated key features of MARCH, most notably renal dysplasia, cerebellar hypoplasia and craniofacial abnormalities. These phenotypes could be rescued by full-length but not truncated human CEP55 message. Finally, we expressed the truncated form of CEP55 in human cells, where we observed a failure of truncated protein to localise to the midbody, leading to abscission failure and multinucleated daughter cells.

Conclusions

CEP55 loss of function mutations likely underlie MARCH, a novel multiple congenital anomaly syndrome. This association expands the involvement of centrosomal proteins in human genetic disorders by highlighting a role in midbody function.

Utility of whole-exome sequencing for those near the end of the diagnostic odyssey: time to address gaps in care

An accurate diagnosis is an integral component of patient care for children with rare genetic disease. Recent advances in sequencing, in particular whole‐exome sequencing (WES), are identifying the genetic basis of disease for 25–40% of patients. The diagnostic rate is probably influenced by when in the diagnostic process WES is used. The Finding Of Rare Disease GEnes (FORGE) Canada project was a nation‐wide effort to identify mutations for childhood‐onset disorders using WES. Most children enrolled in the FORGE project were toward the end of the diagnostic odyssey. The two primary outcomes of FORGE were novel gene discovery and the identification of mutations in genes known to cause disease. In the latter instance, WES identified mutations in known disease genes for 105 of 362 families studied (29%), thereby informing the impact of WES in the setting of the diagnostic odyssey. Our analysis of this dataset showed that these known disease genes were not identified prior to WES enrollment for two key reasons: genetic heterogeneity associated with a clinical diagnosis and atypical presentation of known, clinically recognized diseases. What is becoming increasingly clear is that WES will be paradigm altering for patients and families with rare genetic diseases.

A novel CCBE1 mutation leading to a mild form of hennekam syndrome: case report and review of the literature

Background

Mutations in CCBE1 have been found to be responsible for a subset of families with autosomal recessive Hennekam syndrome. Hennekam syndrome is defined as the combination of generalized lymphatic dysplasia (ie. lymphedema and lymphangiectasia), variable intellectual disability and characteristic dysmorphic features. The patient we describe here has a lymphatic dysplasia without intellectual disability or dysmorphism caused by mutation in CCBE1, highlighting the phenotypic variability that can be seen with abnormalities in this gene.

Case presentation

Our patient is a 5 week old child of Pakistani descent who presented to our center with generalized edema, ascites, and hypoalbuminemia. She was diagnosed with a protein losing enteropathy secondary to segmental primary intestinal lymphangiectasia. As the generalized edema resolved, it became clear that she had mild persistent lymphedema in her hands and feet. No other abnormalities were noted on examination and development was unremarkable at 27 months of age. Given the suspected genetic etiology and the consanguinity in the family, we used a combination of SNP genotyping and exome sequencing to identify the underlying cause of her disease. We identified several large stretches of homozygosity in the patient that allowed us to sort the variants found in the patient’s exome to identify p.C98W in CCBE1 as the likely pathogenic variant.

Conclusions

CCBE1 mutation analysis should be considered in all patients with unexplained lymphatic dysplasia even without the other features of classic Hennekam syndrome.

SCN1A mutation associated with intractable myoclonic epilepsy and migraine headache

Mutations in the SCN1A gene are associated with a variety of epilepsy syndromes and more recently with familial hemiplegic migraine. The spectrum of phenotypes can be quite broad even within the same family and with the same mutation. Here we describe a child with intractable myoclonic epilepsy and autism spectrum disorder who carries an inherited mutation in SCN1A (c.3521C>G, p.T1174S). Previous reports suggest this mutation causes familial hemiplegic migraine and interestingly both the patient's mother, who also carries the mutation, and the patient's maternal grandmother, have frequent migraines with aura.

Origin of a prenatal mosaic supernumerary neocentromeric derivative chromosome 13 determined by QF-PCR

Neocentromeres are mitotically stable human derivative centromeres without alpha-satellite DNA which are able to provide stability to rearranged chromosome fragments that would otherwise be acentric and rapidly lost. A female fetus was found to be mosaic for a supernumerary marker chromosome: 47,XX,+mar[3]/46,XX[36]. The marker was identified by fluorescence in situ hybridization and G-band as an inversion duplication of 13q21→13qter, with a neocentromere present at 13q21, in approximately 9% of colonies examined. Parental blood karyotypes were normal. QF-PCR performed on blood samples from both parents and the second amniotic fluid sample showed evidence of a second maternal allele at markers D13S258 (13q21) and D13S628 (13q31-q32), indicating formation at maternal meiosis I/II. This is the first reported case where the detection and origin of a low-level mosaic prenatal neo(13) were confirmed by QF-PCR.

TMEM237 is mutated in individuals with a Joubert syndrome related disorder and expands the role of the TMEM family at the ciliary transition zone

Joubert syndrome related disorders (JSRDs) have broad but variable phenotypic overlap with other ciliopathies. The molecular etiology of this overlap is unclear but probably arises from disrupting common functional module components within primary cilia. To identify additional module elements associated with JSRDs, we performed homozygosity mapping followed by next-generation sequencing (NGS) and uncovered mutations in TMEM237 (previously known as ALS2CR4). We show that loss of the mammalian TMEM237, which localizes to the ciliary transition zone (TZ), results in defective ciliogenesis and deregulation of Wnt signaling. Furthermore, disruption of Danio rerio (zebrafish) tmem237 expression produces gastrulation defects consistent with ciliary dysfunction, and Caenorhabditis elegans jbts-14 genetically interacts with nphp-4, encoding another TZ protein, to control basal body-TZ anchoring to the membrane and ciliogenesis. Both mammalian and C. elegans TMEM237/JBTS-14 require RPGRIP1L/MKS5 for proper TZ localization, and we demonstrate additional functional interactions between C. elegans JBTS-14 and MKS-2/TMEM216, MKSR-1/B9D1, and MKSR-2/B9D2. Collectively, our findings integrate TMEM237/JBTS-14 in a complex interaction network of TZ-associated proteins and reveal a growing contribution of a TZ functional module to the spectrum of ciliopathy phenotypes.

Recurrent posterior circulation stroke in an infant with basilar artery aneurysm

Arterial ischemic stroke involving the posterior circulation is uncommon in children. The underlying etiologies and risk factors predisposing to posterior circulation stroke include vasculopathies, intracranial trauma, cardiac disease, infection, and hematologic disorders. However, in many children with posterior circulation stroke, the underlying mechanisms are poorly understood. We describe a 14-month-old infant with recurrent arterial ischemic stroke involving the posterior circulation secondary to an aneurysm of the basilar artery.

The interaction of Piasy with Trim32, an E3-ubiquitin ligase mutated in limb-girdle muscular dystrophy type 2H, promotes Piasy degradation and regulates UVB-induced keratinocyte apoptosis through NFkappaB

Protein inhibitors of activated STATs (PIAS) family members are ubiquitin-protein isopeptide ligase-small ubiquitin-like modifier ligases for diverse transcription factors. However, the regulation of PIAS protein activity in cells is poorly understood. Previously, we reported that expression of Trim32, a RING domain ubiquitin-protein isopeptide ligase-ubiquitin ligase mutated in human limb-girdle muscular dystrophy type 2H (LGMD2H) and Bardet-Biedl syndrome, is elevated during mouse skin carcinogenesis, protecting keratinocytes from apoptosis induced by UVB and tumor necrosis factor-alpha (TNFalpha). Here we report that Trim32 interacts with Piasy and promotes Piasy ubiquitination and degradation. Ubiquitination of Piasy by Trim32 could be reproduced in vitro using purified components. Their interaction was induced by treatment with UVB/TNFalpha and involved redistribution of Piasy from the nucleus to the cytoplasm, where it accumulated in cytoplasmic granules that colocalized with Trim32. Piasy destabilization and ubiquitination required an intact RING domain in Trim32. The LGMD2H-associated missense point mutation prevented Trim32 binding to Piasy, and human Piasy failed to colocalize with human Trim32 in fibroblasts isolated from an LGMD2H patient. Trim32 expression increased the transcriptional activity of NFkappaB in epidermal keratinocytes, both under basal treatment and after UVB/TNFalpha treatment. Conversely, Piasy inhibited NFkappaB activity under the same conditions and sensitized keratinocytes to apoptosis induced by TNFalpha and UVB. Our results indicate that, by controlling Piasy stability, Trim32 regulates UVB-induced keratinocyte apoptosis through induction of NFkappaB and suggests loss of function of Trim32 in LGMD2H.

The most common mutation in FKRP causing limb girdle muscular dystrophy type 2I (LGMD2I) may have occurred only once and is present in Hutterites and other populations

Limb girdle muscular dystrophy (LGMD) is common in the Hutterite population of North America. We previously identified a mutation in the TRIM32 gene in chromosome region 9q32, causing LGMD2H in approximately two-thirds of the 60 Hutterite LGMD patients studied to date. A genomewide scan was undertaken in five families who did not show linkage to the LGMD2H locus on chromosome 9. A second LGMD locus, LGMD2I, was identified in chromosome region 19q13.3, and the causative mutation was identified as c.826C>A (L276I), a missense mutation in the FKRP gene. A comparison of the clinical characteristics of the two LGMD patient groups in this population reveals some differences. LGMD2I patients generally have an earlier age at diagnosis, a more severe course, and higher serum creatine kinase (CK) levels. In addition, some of these patients show calf hypertrophy, cardiac symptoms, and severe reactions to general anesthesia. None of these features are present among LGMD2H patients. A single common haplotype surrounding the FKRP gene was identified in the Hutterite LGMD2I patients. An identical core haplotype was also identified in 19 other non-Hutterite LGMD2I patients from Europe, Canada, and Brazil. The occurrence of this mutation on a common core haplotype suggests that L276I is a founder mutation that is dispersed among populations of European origin.

Hutterite brothers both affected with two forms of limb girdle muscular dystrophy: LGMD2H and LGMD2I

Limb girdle muscular dystrophy (LGMD) is very common in the Hutterite population of the North American Prairies. We have recently reported the homozygous c.1459G>A mutation in TRIM32 associated with LGMD2H. We have also identified Hutterite patients with LGMD2I, homozygous for the common c.826C>A mutation in FKRP. To date, all Hutterites with LGMD have been shown to be homozygous for either the TRIM32 or FKRP mutation. We now report a Hutterite family in which both parents and five sons were all found to be homozygous for the TRIM32 mutation. The father had slowly progressive proximal muscle weakness, whereas three sons and their mother, all currently asymptomatic, had normal physical examinations. The remaining two sons (7 and 10 years old), presented with mild decrease in stamina, had normal neuromuscular examinations and were found to be homozygous for the FKRP mutation in addition to the TRIM32 mutation. These two boys do not differ in age at or mode of presentation, physical findings, or serum CK levels compared to age-matched individuals affected with LGMD2I alone. This suggests that the effects of these two mutations are not acting synergistically at this time. It remains to be seen whether there will be signs of interaction between these two mutations as the patients get older.

Commonality ofTRIM32mutation in causing sarcotubular myopathy and LGMD2H

Sarcotubular myopathy (OMIM 268950) is a rare autosomal recessive myopathy first described in two Hutterite brothers from South Dakota and in two non-Hutterite brothers from Germany. We report that sarcotubular myopathy (STM) is caused by mutation in TRIM32, the gene encoding the tripartite motif-containing protein 32. TRIM32 was found to be the gene mutated in limb girdle muscular dystrophy type 2H (LGMD2H [OMIM 254110]), a disorder that has been confined to the Hutterite population. The TRIM32 mutation found in the STM patients is identical to the causative mutation for LGMD2H (D487N), Haplotype analysis shows that the disease chromosomes share common ancestry.

Neuropathological, biochemical and molecular findings in a glutaric acidemia type 1 cohort

Glutaric acidemia type 1 (GA-1) is an autosomal recessive disorder characterized by a deficiency of glutaryl-CoA dehydrogenase (GCDH) activity. GA-1 is often associated with an acute encephalopathy between 6 and 18 months of age that causes striatal damage resulting in a severe dystonic movement disorder. Ten autopsy cases have been previously described. Our goal is to understand the disorder better so that treatments can be designed. Therefore, we present the neuropathological features of six additional cases (8 months-40 years), all North American aboriginals with the identical homozygous mutation. This cohort displays similar pathological characteristics to those previously described. Four had macroencephaly. All had striatal atrophy with severe loss of medium-sized neurons. We present several novel findings. This natural time course study allows us to conclude that neuron loss occurs shortly after the encephalopathical crisis and does not progress. In addition, we demonstrate mild loss of large striatal neurons, spongiform changes restricted to brainstem white matter and a mild lymphocytic infiltrate in the early stages. Reverse transcriptase-PCR to detect the GCDH mRNA revealed normal and truncated transcripts similar to those in fibroblasts. All brain regions demonstrated markedly elevated concentrations of GA (3770-21 200 nmol/g protein) and 3-OH-GA (280-740 nmol/g protein), with no evidence of striatal specificity or age dependency. The role of organic acids as toxic agents and as osmolytes is discussed. The pathogenesis of selective neuronal loss cannot be explained on the basis of regional genetic and/or metabolic differences. A suitable animal model for GA-1 is needed.

Cardiac and respiratory failure in limb-girdle muscular dystrophy 2I

Mutations in the gene encoding fukutin-related protein cause limb-girdle muscular dystrophy 2I. In this multicenter retrospective analysis of 38 patients, 55.3% had cardiac abnormalities, of which 24% had developed cardiac failure. Heterozygotes for the common C826A mutation developed cardiac involvement earlier than homozygotes. All patients initially improved while receiving standard therapy. Independent of cardiac status, forced vital capacity was below 75% in 44.4% of the patients. There was no absolute correlation between skeletal muscle weakness and cardiomyopathy or respiratory insufficiency. These complications are a primary part of this specific type of limb-girdle muscular dystrophy, with important implications for management.

Limb-girdle muscular dystrophy type 2H associated with mutation in TRIM32, a putative E3-ubiquitin-ligase gene

Limb-girdle muscular dystrophy type 2H (LGMD2H) is a mild autosomal recessive myopathy that was first described in the Manitoba Hutterite population. Previous studies in our laboratory mapped the causative gene for this disease to a 6.5-Mb region in chromosomal region 9q31-33, flanked by D9S302 and D9S1850. We have now used additional families and a panel of 26 microsatellite markers to construct haplotypes. Twelve recombination events that reduced the size of the candidate region to 560 kb were identified or inferred. This region is flanked by D9S1126 and D9S737 and contains at least four genes. Exons of these genes were sequenced in one affected individual, and four sequence variations were identified. The families included in our study and 100 control individuals were tested for these variations. On the basis of our results, the mutation in the tripartite-motif-containing gene (TRIM32) that replaces aspartate with asparagine at position 487 appears to be the causative mutation of LGMD2H. All affected individuals were found to be homozygous for D487N, and this mutation was not found in any of the controls. This mutation occurs in an NHL (named after the proteins NCL1, HT2A, and LIN-41) domain at a position that is highly conserved. NHL domains are known to be involved in protein-protein interactions. Although the function of TRIM32 is unknown, current knowledge of the domain structure of this protein suggests that it may be an E3-ubiquitin ligase. If proven, this represents a new pathogenic mechanism leading to muscular dystrophy.