MN1 C-terminal truncation syndrome is a novel neurodevelopmental and craniofacial disorder with partial rhombencephalosynapsis.

MN1 encodes a transcriptional co-regulator without homology to other proteins, previously implicated in acute myeloid leukaemia and development of the palate. Large deletions encompassing MN1 have been reported in individuals with variable neurodevelopmental anomalies and non-specific facial features. We identified a cluster of de novo truncating mutations in MN1 in a cohort of 23 individuals with strikingly similar dysmorphic facial features, especially midface hypoplasia, and intellectual disability with severe expressive language delay. Imaging revealed an atypical form of rhombencephalosynapsis, a distinctive brain malformation characterized by partial or complete loss of the cerebellar vermis with fusion of the cerebellar hemispheres, in 8/10 individuals. Rhombencephalosynapsis has no previously known definitive genetic or environmental causes. Other frequent features included perisylvian polymicrogyria, abnormal posterior clinoid processes and persistent trigeminal artery. MN1 is encoded by only two exons. All mutations, including the recurrent variant p.Arg1295* observed in 8/21 probands, fall in the terminal exon or the extreme 3' region of exon 1, and are therefore predicted to result in escape from nonsense-mediated mRNA decay. This was confirmed in fibroblasts from three individuals. We propose that the condition described here, MN1 C-terminal truncation (MCTT) syndrome, is not due to MN1 haploinsufficiency but rather is the result of dominantly acting C-terminally truncated MN1 protein. Our data show that MN1 plays a critical role in human craniofacial and brain development, and opens the door to understanding the biological mechanisms underlying rhombencephalosynapsis.

Biochemical signatures mimicking multiple carboxylase deficiency in children with mutations in MT-ATP6.

Elevations of specific acylcarnitines in blood reflect carboxylase deficiencies, and have utility in newborn screening for life-threatening organic acidemias and other inherited metabolic diseases. In this report, we describe a newly-identified association of biochemical features of multiple carboxylase deficiency in individuals harboring mitochondrial DNA (mtDNA) mutations in MT-ATP6 and in whom organic acidemias and multiple carboxylase deficiencies were excluded. Using retrospective chart review, we identified eleven individuals with abnormally elevated propionylcarnitine (C3) or hydroxyisovalerylcarnitine (C5OH) with mutations in MT-ATP6, most commonly m.8993T>G in high heteroplasmy or homoplasmy. Most patients were ascertained on newborn screening; most had normal enzymatic or molecular genetic testing to exclude biotinidase and holocarboxylase synthetase deficiencies. MT-ATP6 is associated with some cases of Leigh disease; clinical outcomes in our cohort ranged from death from neurodegenerative disease in early childhood to clinically and developmentally normal after several years of follow-up. These cases expand the biochemical phenotype associated with MT-ATP6 mutations, especially m.8993T>G, to include acylcarnitine abnormalities mimicking carboxylase deficiency states. Clinicians should be aware of this association and its implications for newborn screening, and consider mtDNA sequencing in patients exhibiting similar acylcarnitine abnormalities that are biotin-unresponsive and in whom other enzymatic deficiencies have been excluded.

Conducting an investigator-initiated randomized double-blinded intervention trial in acute decompensation of inborn errors of metabolism: Lessons from the N-Carbamylglutamate Consortium.

Organic acidemias and urea cycle disorders are ultra-rare inborn errors of metabolism characterized by episodic acute decompensation, often associated with hyperammonemia, resulting in brain edema and encephalopathy. Retrospective reports and translational studies suggest that N-carbamylglutamate (NCG) may be effective in reducing ammonia levels during acute decompensation in two organic acidemias, propionic and methylmalonic acidemia (PA and MMA), and in two urea cycle disorders, carbamylphosphate synthetase 1 and ornithine transcarbamylase deficiency (CPSD and OTCD). We established the 9-site N-carbamylglutamate Consortium (NCGC) in order to conduct two randomized double-blind, placebo-controlled trials of NCG in acute hyperammonemia of PA, MMA, CPSD and OTCD. Conducting clinical trials is challenging in any disease, but poses unique barriers and risks in the ultra-rare disorders. As the number of clinical trials in orphan diseases increases, evaluating the successes and opportunities for improvement in such trials is essential. We summarize herein the design, methods, experiences, challenges and lessons from the NCGC-conducted trials.

Erratum: A de novo 2.78-Mb duplication on chromosome 21q22.11 implicates candidate genes in the partial trisomy 21 phenotype.

[This corrects the article DOI: 10.1038/npjgenmed.2016.3.].

Guidelines for diagnosis and management of the cobalamin-related remethylation disorders cblC, cblD, cblE, cblF, cblG, cblJ and MTHFR deficiency.

BACKGROUND: Remethylation defects are rare inherited disorders in which impaired remethylation of homocysteine to methionine leads to accumulation of homocysteine and perturbation of numerous methylation reactions. OBJECTIVE: To summarise clinical and biochemical characteristics of these severe disorders and to provide guidelines on diagnosis and management. DATA SOURCES: Review, evaluation and discussion of the medical literature (Medline, Cochrane databases) by a panel of experts on these rare diseases following the GRADE approach. KEY RECOMMENDATIONS: We strongly recommend measuring plasma total homocysteine in any patient presenting with the combination of neurological and/or visual and/or haematological symptoms, subacute spinal cord degeneration, atypical haemolytic uraemic syndrome or unexplained vascular thrombosis. We strongly recommend to initiate treatment with parenteral hydroxocobalamin without delay in any suspected remethylation disorder; it significantly improves survival and incidence of severe complications. We strongly recommend betaine treatment in individuals with MTHFR deficiency; it improves the outcome and prevents disease when given early.

De novo and inherited SCN8A epilepsy mutations detected by gene panel analysis.

OBJECTIVES: To determine the incidence of pathogenic SCN8A variants in a cohort of epilepsy patients referred for clinical genetic testing. We also investigated the contribution of SCN8A to autism spectrum disorder, intellectual disability, and neuromuscular disorders in individuals referred for clinical genetic testing at the same testing laboratory. METHODS: Sequence data from 275 epilepsy panels screened by Emory Genetics Laboratory were reviewed for variants in SCN8A. Two additional cases with variants in SCN8A were ascertained from other testing laboratories. Parental samples were tested for variant segregation and clinical histories were examined. SCN8A variants detected from gene panel analyses for autism spectrum disorder, intellectual disability, and neuromuscular disorders were also examined. RESULTS: Five variants in SCN8A were identified in five individuals with epilepsy. Three variants were de novo, one was inherited from an affected parent, and one was inherited from an unaffected parent. Four of the individuals have epilepsy and developmental delay/intellectual disability. The remaining individual has a milder epilepsy presentation without cognitive impairment. We also identified an amino acid substitution at an evolutionarily conserved SCN8A residue in a patient who was screened on the autism spectrum disorder panel. Additionally, we examined the distribution of pathogenic SCN8A variants across the Nav1.6 channel and identified four distinct clusters of variants. These clusters are primarily located in regions of the channel that are important for the kinetics of channel inactivation. CONCLUSIONS: Variants in SCN8A may be responsible for a spectrum of epilepsies as well as other neurodevelopmental disorders without seizures. The predominant pathogenic mechanism appears to involve disruption of channel inactivation, leading to gain-of-function effects.

Cerebrotendinous Xanthomatosis Presenting with Infantile Spasms and Intellectual Disability.

Cerebrotendinous xanthomatosis (CTX) is an inborn error of metabolism leading to progressive multisystem disease. Symptoms often begin in the first decade of life with chronic diarrhea, cataracts, developmental delay, intellectual disability, and cerebellar or pyramidal dysfunction. Later manifestations include tendon xanthomas, polyneuropathy, and abnormal neuroimaging. Pathogenic biallelic variants in CYP27A1 leading to compromised function of sterol 27-hydroxylase result in accumulation of detectable toxic intermediates of bile acid synthesis rendering both genetic and biochemical testing effective diagnostic tools. Effective treatment with chenodeoxycholic acid is available, making early diagnosis critical for patient care. Here we report a new patient with CTX and describe the early signs of disease in this patient. Initial symptoms included infantile spasms, which have not previously been reported in CTX. Developmental delay, mild intellectual disability with measured cognitive decline in childhood, was also observed. These clinical signs do not traditionally compel testing for CTX, and we highlight the need to consider this rare but treatable disorder among the differential diagnosis of children with similar clinical presentation. Increased awareness of early signs of CTX is important for improving time to diagnosis for this patient population.

A de novo 2.78-Mb duplication on chromosome 21q22.11 implicates candidate genes in the partial trisomy 21 phenotype.

Down syndrome (DS) is the most common genetic cause of intellectual disability (ID) and in the majority of cases is the result of complete trisomy 21. The hypothesis that the characteristic DS clinical features are due to a single DS critical region (DSCR) at distal chromosome 21q has been refuted by recently reported segmental trisomy 21 cases characterised by microarray-based comparative genomic hybridisation (aCGH). These rare cases have implicated multiple regions on chromosome 21 in the aetiology of distinct features of DS; however, the map of chromosome 21 copy-number aberrations and their associated phenotypes remains incompletely defined. We report a child with ID who was deemed very high risk for DS on antenatal screening (1 in 13) and has partial, but distinct, dysmorphologic features of DS without congenital heart disease (CHD). Oligonucleotide aCGH testing of the proband detected a previously unreported de novo 2.78-Mb duplication on chromosome 21q22.11 that includes 16 genes; however, this aberration does not harbour any of the historical DSCR genes (APP, DSCR1, DYRK1A and DSCAM). This informative case implicates previously under-recognised candidate genes (SOD1, SYNJ1 and ITSN1) in the pathogenesis of specific DS clinical features and supports a critical region for CHD located more distal on chromosome 21q. In addition, this unique case illustrates how the increasing resolution of microarray and high-throughput sequencing technologies can continue to reveal new biology and enhance understanding of widely studied genetic diseases that were originally described over 50 years ago.

Clinical phenotype, biochemical profile, and treatment in 19 patients with arginase 1 deficiency.

BACKGROUND: Arginase 1 (ARG1) deficiency is a rare urea cycle disorder (UCD). This hypothesis-generating study explored clinical phenotypes, metabolic profiles, molecular genetics, and treatment approaches in a cohort of children and adults with ARG1 deficiency to add to our understanding of the underlying pathophysiology. METHODS: Clinical data were retrieved retrospectively from physicians using a questionnaire survey. Plasma aminoacids, guanidinoacetate (GAA), parameters indicating oxidative stress and nitric oxide (NO) synthesis as well as asymmetric dimethylarginine (ADMA) were measured at a single study site. RESULTS: Nineteen individuals with ARG1 deficiency and 19 matched controls were included in the study. In patients, paraparesis, cognitive impairment, and seizures were significantly associated suggesting a shared underlying pathophysiology. In patients plasma GAA exceeded normal ranges and plasma ADMA was significantly elevated. Compared to controls, nitrate was significantly higher, and the nitrite:nitrate ratio significantly lower in subjects with ARG1 deficiency suggesting an advantage for NO synthesis by inducible NO synthase (iNOS) over endothelial NOS (eNOS). Logistic regression revealed no significant impact of any of the biochemical parameters (including arginine, nitrates, ADMA, GAA, oxidative stress) or protein restriction on long-term outcome. CONCLUSION: Three main hypotheses which must be evaluated in a hypothesis driven confirmatory study are delineated from this study: 1) clinical manifestations in ARG1 deficiency are not correlated with arginine, protein intake, ADMA, nitrates or oxidative stress. 2) GAA is elevated and may be a marker or an active part of the pathophysiology of ARG1 deficiency. 3) Perturbations of NO metabolism merit future attention in ARG1 deficiency.

Optic neuropathy in late-onset neurodegenerative Chédiak-Higashi syndrome.

BACKGROUND: The classic form of Chédiak-Higashi syndrome (CHS), an autosomal recessive disorder of lysosomal trafficking with childhood onset caused by mutations in ITALIC! LYST, is typified ophthalmologically by ocular albinism with vision loss attributed to foveal hypoplasia or nystagmus. Optic nerve involvement and ophthalmological manifestations of the late-onset neurodegenerative form of CHS are rarely reported and poorly detailed. METHODS: Case series detailing ophthalmological and neurological findings in three adult siblings with the late-onset form of CHS. RESULTS: All three affected siblings lacked features of ocular albinism and demonstrated significant optic nerve involvement as evidenced by loss of colour and contrast vision, central visual field loss, optic nerve pallor, retinal nerve fibre layer thinning by optical coherence tomography (OCT) and abnormal visual evoked potential, with severity corresponding linearly to age of the sibling and severity of neurological disease. Further, unusual prominence of a 'third line' on macular OCT that may be due to abnormal melanosomes was seen in all three siblings and in their father. Neurological involvement included parkinsonism, cerebellar ataxia and spastic paraparesis. CONCLUSIONS: This report expands the ophthalmological phenotype of the late-onset neurodegenerative form of CHS to include optic neuropathy with progressive vision loss, even in the absence of ocular albinism, and abnormal prominence of the interdigitation zone between cone outer segment tips and apical processes of retinal pigment epithelium cells on macular OCT.

Ocular disease in the cobalamin C defect: a review of the literature and a suggested framework for clinical surveillance.

The association between combined methylmalonic acidemia and homocystinuria of cblC type (cobalamin C defect, cblC) and ocular disease is now well recognized, and is a significant component of morbidity and disability associated with the condition. In this review, through collation of historically reported cases of early- and late-onset cblC and previously unreported cases, we have attempted to characterize the epidemiology, clinical features, and pathomechanisms of individual ocular features of cblC. These data suggest that maculopathy and nystagmus with abnormal vision are extremely common and affect the majority of children with early-onset cblC, usually before school age; strabismus and optic atrophy are also seen at relatively high frequency. The timing of progression of macular disease may coincide with a critical period of postnatal foveal development. Maculopathy and retinal disease may be subclinical and show only partial correlation with the extent of visual deficits, and visual deterioration may be relentlessly progressive in spite of aggressive treatment of biochemical abnormalities. In later-onset forms of the disease, visual loss and ocular complications appear to be infrequent. Finally, we discuss investigational strategies in diagnosing and characterizing eye disease in individuals with cblC, explore possible therapeutic avenues that may attenuate progression and severity of eye disease, and propose a clinical surveillance guideline for monitoring progression of ocular disease in children and adults with cblC.

Differential diagnosis of Mendelian and mitochondrial disorders in patients with suspected multiple sclerosis.

Several single gene disorders share clinical and radiologic characteristics with multiple sclerosis and have the potential to be overlooked in the differential diagnostic evaluation of both adult and paediatric patients with multiple sclerosis. This group includes lysosomal storage disorders, various mitochondrial diseases, other neurometabolic disorders, and several other miscellaneous disorders. Recognition of a single-gene disorder as causal for a patient's 'multiple sclerosis-like' phenotype is critically important for accurate direction of patient management, and evokes broader genetic counselling implications for affected families. Here we review single gene disorders that have the potential to mimic multiple sclerosis, provide an overview of clinical and investigational characteristics of each disorder, and present guidelines for when clinicians should suspect an underlying heritable disorder that requires diagnostic confirmation in a patient with a definite or probable diagnosis of multiple sclerosis.

Impact of tumor location and pathological discordance on survival of children with midline high-grade gliomas treated on Children's Cancer Group high-grade glioma study CCG-945.

Children with high-grade glioma (HGG) have a poor prognosis compared to those with low-grade glioma (LGG). Adjuvant chemotherapy may be beneficial, but its optimal use remains undetermined. Histology and extent of resection are important prognostic factors. We tested the hypothesis that patients with midline HGG treated on Children's Cancer Group Study (CCG) CCG-945 have a worse prognosis compared to the entire group. Of 172 children eligible for analysis, 60 had midline tumors primarily localized to the thalamus, hypothalamus and basal ganglia. Time-to-progression and death were determined from the date of initial diagnosis, and survival curves were calculated. Univariate analyses were undertaken for extent of resection, chemotherapy regimen, anatomic location, histology, proliferation index, MGMT status and p53 over-expression. For the entire midline tumor group, 5-year PFS and OS were 18.3 ± 4.8 and 25 ± 5.4 %, respectively. Many patients only had a biopsy (43.3 %). The sub-groups with near/total resection and hypothalamic location appeared to have better PFS and OS. However, the effect of tumor histology on OS was significant for children with discordant diagnoses on central pathology review of LGG compared to HGG. Proliferative index (MIB-1 > 36 %), MGMT and p53 over-expression correlated with poor outcomes. Children treated on CCG-945 with midline HGG have a worse prognosis when compared to the entire group. The midline location may directly influence the extent of resection. Central pathology review and entry of patients on clinical trials continue to be priorities to improve outcomes for children with HGG.

Neurologic and neurodevelopmental phenotypes in young children with early-treated combined methylmalonic acidemia and homocystinuria, cobalamin C type.

Abnormal neurodevelopment has been widely reported in combined methylmalonic aciduria (MMA) and homocystinuria, cblC type (cblC disease), but neurodevelopmental phenotypes in cblC have not previously been systematically studied. We sought to further characterize developmental neurology in children with molecularly-confirmed cblC. Thirteen children at our center with cblC, born since implementation of expanded newborn screening in New York State, undertook standard-of-care evaluations with a pediatric neurologist and pediatric ophthalmologist. At most recent follow-up (mean age 50 months, range 9-84 months), of twelve children with early-onset cblC, three (25%) had a history of clinical seizures and two (17%) meet criteria for microcephaly. A majority of children had hypotonia and nystagmus. Twelve out of thirteen (92%) underwent neurodevelopmental evaluation (mean age 41 months; range 9-76 months), each child tested with standardized parental interviews and, where possible, age- and disability-appropriate neuropsychological batteries. All patients showed evidence of developmental delay with the exception of one patient with a genotype predictive of attenuated disease and near-normal biochemical parameters. Neurodevelopmental deficits were noted most prominently in motor skills, with relative preservation of socialization and communication skills. Nine children with early-onset cblC underwent magnetic resonance imaging and spectroscopy (MRI/MRS) at mean age of 47 months (range 6-81 months); common abnormalities included callosal thinning, craniocaudally short pons, and increased T2 FLAIR signal in periventricular and periatrial white matter. Our study further characterizes variable neurodevelopmental phenotypes in treated cblC, and provides insights into the etiopathogenesis of disordered neurodevelopment frequently encountered in cblC. Plasma homocysteine and MMA, routinely measured at clinical follow-up, may be poor predictors for neurodevelopmental outcomes. Additional data from large, prospective, multi-center natural history studies are required to more accurately define the role of these metabolites and others, as well as that of other genetic and environmental factors in the etiopathogenesis of the neurologic components of this disorder.

Atypical Chédiak-Higashi syndrome with attenuated phenotype: three adult siblings homozygous for a novel LYST deletion and with neurodegenerative disease.

BACKGROUND: Mutations in LYST, a gene encoding a putative lysosomal trafficking protein, cause Chédiak-Higashi syndrome (CHS), an autosomal recessive disorder typically characterized by infantile-onset hemophagocytic syndrome and immunodeficiency, and oculocutaneous albinism. A small number of reports of rare, attenuated forms of CHS exist, with affected individuals exhibiting progressive neurodegenerative disease beginning in early adulthood with cognitive decline, parkinsonism, features of spinocerebellar degeneration, and peripheral neuropathy, as well as subtle pigmentary abnormalities and subclinical or absent immune dysfunction. METHODS: In a consanguineous Pakistani kindred with clinical phenotypes consistent with attenuated CHS, we performed SNP array-based homozygosity mapping and whole gene sequencing of LYST. RESULTS: We identified three individuals homozygous for a novel six base pair in-frame deletion in LYST (c.9827_9832ATACAA), predicting the loss of asparagine and threonine residues from the LYST transcript (p.Asn3276_Thr3277del), and segregating with the phenotype in this family. CONCLUSIONS: We further characterize the neurologic features of the attenuated form of CHS, and discuss pathophysiologic mechanisms underlying the neurodegenerative components of CHS. Attenuated CHS is phenotypically heterogenous and should be considered when young adults develop neurodegenerative disease and have pigmentary abnormalities. We briefly discuss surveillance and management of patients with CHS-related neurodegeneration.

Phenotypic heterogeneity in a family with a small atypical microduplication of chromosome 22q11.2 involving TBX1.

The chromosome 22q11.2 region is commonly involved in non-allelic homologous recombination (NAHR) events. Microduplications of 22q11.2, usually involving a 3 Mb or 1.5 Mb region constitute the 22q11 microduplication syndrome. Both microdeletions and microduplications of 22q11.21 are reported to share several phenotypic characteristics, including dysmorphic facial features, velopharyngeal insufficiency, congenital heart disease, urogenital abnormalities, and immunologic defects. We report a child who presented at 8 months of age for evaluation of microcephaly and mild motor delay. Head circumference at birth, at 8 months, and at 19 months of age was below the 3rd centile. Other findings included left-sided cryptorchidism and developmental dysplasia of the left hip. In addition, echocardiography revealed a restrictive patent ductus arteriosus. Chromosomal microarray analysis using Affymetrix Genome-Wide Human SNP Array 6.0 revealed a novel 437 kb interstitial duplication at 22q11.21, involving TBX1, whose breakpoints did not coincide with known low copy repeat (LCR) regions. The same duplication was confirmed by fluorescent in situ hybridization (FISH) in the patient's mother and an older sister. The mother has a history of anxiety disorder and depression. The sister had a history of delayed motor milestones. None of the three duplication carriers has any documented renal anomalies or other significant medical problems. This report demonstrates the clinical heterogeneity associated with microduplications of 22q11.2 and illustrates the difficulties related to providing prognostic information and accurate genetic counseling to families when this finding is detected. The described microduplication is the smallest in this genomic region reported to date and further implicates abnormal gene dosage of TBX1 in disorders resulting from 22q11.2 rearrangements.