The clinical and genetic spectrum of autosomal-recessive TOR1A-related disorders.

In the field of rare diseases, progress in molecular diagnostics led to the recognition that variants linked to autosomal-dominant neurodegenerative diseases of later onset can, in the context of biallelic inheritance, cause devastating neurodevelopmental disorders and infantile or childhood-onset neurodegeneration. TOR1A-associated arthrogryposis multiplex congenita 5 (AMC5) is a rare neurodevelopmental disorder arising from biallelic variants in TOR1A, a gene that in the heterozygous state is associated with torsion dystonia-1 (DYT1 or DYT-TOR1A), an early-onset dystonia with reduced penetrance. While 15 individuals with AMC5-TOR1A have been reported (less than 10 in detail), a systematic investigation of the full disease-associated spectrum has not been conducted. Here, we assess the clinical, radiological and molecular characteristics of 57 individuals from 40 families with biallelic variants in TOR1A. Median age at last follow-up was 3 years (0-24 years). Most individuals presented with severe congenital flexion contractures (95%) and variable developmental delay (79%). Motor symptoms were reported in 79% and included lower limb spasticity and pyramidal signs, as well as gait disturbances. Facial dysmorphism was an integral part of the phenotype, with key features being a broad/full nasal tip, narrowing of the forehead and full cheeks. Analysis of disease-associated manifestations delineated a phenotypic spectrum ranging from normal cognition and mild gait disturbance to congenital arthrogryposis, global developmental delay, intellectual disability, absent speech and inability to walk. In a subset, the presentation was consistent with foetal akinesia deformation sequence with severe intrauterine abnormalities. Survival was 71%, with higher mortality in males. Death occurred at a median age of 1.2 months (1 week-9 years), due to respiratory failure, cardiac arrest or sepsis. Analysis of brain MRI studies identified non-specific neuroimaging features, including a hypoplastic corpus callosum (72%), foci of signal abnormality in the subcortical and periventricular white matter (55%), diffuse white matter volume loss (45%), mega cisterna magna (36%) and arachnoid cysts (27%). The molecular spectrum included 22 distinct variants, defining a mutational hotspot in the C-terminal domain of the Torsin-1A protein. Genotype-phenotype analysis revealed an association of missense variants in the 3-helix bundle domain to an attenuated phenotype, while missense variants near the Walker A/B motif as well as biallelic truncating variants were linked to early death. In summary, this systematic cross-sectional analysis of a large cohort of individuals with biallelic TOR1A variants across a wide age-range delineates the clinical and genetic spectrum of TOR1A-related autosomal-recessive disease and highlights potential predictors for disease severity and survival.

The spectrum of hereditary neuromuscular disorders in the Pakistani population.

Hereditary neuromuscular disorders (NMDs) are a broad group of clinically heterogeneous disorders with varying inheritance patterns, that are associated with over 500 implicated genes. In the context of a highly consanguineous Pakistani population, we expect that autosomal recessive NMDs may have a higher prevalence compared with patients of European descent. This is the first study to offer a detailed description of the spectrum of genes causing hereditary NMDs in the Pakistani population using NGS testing. To study the clinical and genetic profiles of patients presenting for evaluation of a hereditary neuromuscular disorder. This is a retrospective chart review of patients seen in the Neuromuscular Disorders Clinic and referred to the Genetics Clinic with a suspected hereditary neuromuscular disorder, between 2016 and 2020 at the Aga Khan University Hospital, Karachi and Mukhtiar A. Sheikh Hospital, Multan, Pakistan. The genetic testing for these patients included NGS-based single gene sequencing, NGS-based multi-gene panel and whole exome sequencing. In a total of 112 patients studied, 35 (31.3%) were female. The mean age of onset in all patients was 14.6 years (SD ±12.1 years), with the average age at presentation to the clinic of 22.4 years (SD ±14.10 years). Forty-seven (41.9%) patients had a positive genetic test result, 53 (47.3%) had one or more variants of uncertain significance (VUS), and 12 (10.7%) had a negative result. Upon further genotype-phenotype correlation and family segregation analysis, the diagnostic yield improved, with 59 (52.7%) patients reaching a diagnosis of a hereditary NMD. We also report probable founder variants in COL6A2, FKTN, GNE, and SGCB, previously reported in populations that have possible shared ancestry with the Pakistani population. Our findings reemphasizes that the rate of VUSs can be reduced by clinical correlation and family segregation studies.

Paediatric posterior reversible encephalopathy syndrome: is there an association of blood pressure with imaging severity and atypical magnetic resonance characteristics?

BACKGROUND: Posterior reversible encephalopathy syndrome (PRES) is relatively uncommon in paediatric patients; however, its pathophysiology remains obscure. OBJECTIVE: The aims of this study were to find an association or correlation between (1) blood pressures and (2) imaging severity and the presence of atypical imaging features in children with PRES. MATERIALS AND METHODS: We performed a retrospective cross-sectional evaluation in children diagnosed with PRES. We reviewed radiologic findings along with each patient's clinical profile and outcome. We categorised imaging severity into mild, moderate and severe, and assessed the MR imaging pattern, enhancement and diffusion restriction for each child. We assessed both associations and correlations between variables using the chi-square test, Cramer V and Kendall tau b. RESULTS: A total of 63 children met the inclusion criteria (31 boys; mean age 9.7 years). A total of 42 children (67%) had an elevated blood pressure. Imaging showed parieto-occipital lobe involvement pattern in 24 (38%) children, frontal lobe pattern in 25 (40%) and cerebellar involvement in 12 (19%). Three (5%) had haemorrhage, 15 (24%) had contrast enhancement and 19 (30%) had positive diffusion restriction (cytotoxic oedema). We found no statistically significant association between imaging severity and blood pressures (P=0.11), nor any association between blood pressure and atypical imaging findings such as diffusion restriction (P=0.1), enhancement (P=0.11) or haemorrhage (P=0.33). CONCLUSION: According to our results, there is no statistically significant association or correlation between blood pressure and either imaging severity or atypical imaging features in children with PRES. Further prospective studies are warranted.

Clinical, neuroimaging, and molecular spectrum of TECPR2-associated hereditary sensory and autonomic neuropathy with intellectual disability.

Bi-allelic TECPR2 variants have been associated with a complex syndrome with features of both a neurodevelopmental and neurodegenerative disorder. Here, we provide a comprehensive clinical description and variant interpretation framework for this genetic locus. Through international collaboration, we identified 17 individuals from 15 families with bi-allelic TECPR2-variants. We systemically reviewed clinical and molecular data from this cohort and 11 cases previously reported. Phenotypes were standardized using Human Phenotype Ontology terms. A cross-sectional analysis revealed global developmental delay/intellectual disability, muscular hypotonia, ataxia, hyporeflexia, respiratory infections, and central/nocturnal hypopnea as core manifestations. A review of brain magnetic resonance imaging scans demonstrated a thin corpus callosum in 52%. We evaluated 17 distinct variants. Missense variants in TECPR2 are predominantly located in the N- and C-terminal regions containing ß-propeller repeats. Despite constituting nearly half of disease-associated TECPR2 variants, classifying missense variants as (likely) pathogenic according to ACMG criteria remains challenging. We estimate a pathogenic variant carrier frequency of 1/1221 in the general and 1/155 in the Jewish Ashkenazi populations. Based on clinical, neuroimaging, and genetic data, we provide recommendations for variant reporting, clinical assessment, and surveillance/treatment of individuals with TECPR2-associated disorder. This sets the stage for future prospective natural history studies.

PIGG variant pathogenicity assessment reveals characteristic features within 19 families.

PURPOSE: Phosphatidylinositol Glycan Anchor Biosynthesis, class G (PIGG) is an ethanolamine phosphate transferase catalyzing the modification of glycosylphosphatidylinositol (GPI). GPI serves as an anchor on the cell membrane for surface proteins called GPI-anchored proteins (GPI-APs). Pathogenic variants in genes involved in the biosynthesis of GPI cause inherited GPI deficiency (IGD), which still needs to be further characterized. METHODS: We describe 22 individuals from 19 unrelated families with biallelic variants in PIGG. We analyzed GPI-AP surface levels on granulocytes and fibroblasts for three and two individuals, respectively. We demonstrated enzymatic activity defects for PIGG variants in vitro in a PIGG/PIGO double knockout system. RESULTS: Phenotypic analysis of reported individuals reveals shared PIGG deficiency-associated features. All tested GPI-APs were unchanged on granulocytes whereas CD73 level in fibroblasts was decreased. In addition to classic IGD symptoms such as hypotonia, intellectual disability/developmental delay (ID/DD), and seizures, individuals with PIGG variants of null or severely decreased activity showed cerebellar atrophy, various neurological manifestations, and mitochondrial dysfunction, a feature increasingly recognized in IGDs. Individuals with mildly decreased activity showed autism spectrum disorder. CONCLUSION: This in vitro system is a useful method to validate the pathogenicity of variants in PIGG and to study PIGG physiological functions.

CBS mutations and MTFHR SNPs causative of hyperhomocysteinemia in Pakistani children.

Three index patients with hyperhomocysteinemia and ocular anomalies were screened for cystathionine beta synthase (CBS) and methylenetetrahydrofolate reductase (MTHFR) polymorphisms. Genotyping of hyperhomocysteinemia associated MTHFR polymorphisms C677T (rs1801133) and A1298C (rs1801131) was done by PCR-restriction fragment length polymorphism. Sanger sequencing was performed for CBS exonic sequences along with consensus splice sites. In the case of MTHFR polymorphisms, all the patients were heterozygous CT for the single nucleotide polymorphism (SNP) C677T and were therefore carriers of the risk allele (T), while the patients were homozygous CC for the risk genotype of the SNP A1298C. CBS sequencing resulted in the identification of two novel mutations, a missense change (c.467T>C; p.Leu156Pro) in exon 7 and an in-frame deletion (c.808_810del; p.Glu270del) in exon 10. In addition, a recurrent missense mutation (c.770C>T; p.Thr257Met) in exon 10 of the gene was also identified. The mutations were present homozygously in the patients and were inherited from the carrier parents. This is the first report from Pakistan where novel as well as recurrent CBS mutations causing hyperhomocysteinemia and lens dislocation in three patients from different families are being reported with the predicted effect of the risk allele of the MTHFR SNP in causing hyperhomocysteinemia.

Infantile Spasms: Clinical profile and treatment outcomes.

BACKGROUND AND OBJECTIVE: Infantile spasm (IS) is one of the severe epileptic encephalopathies which affect children in early two years of life. Our objective was to determine the clinical profile, etiology and outcome of treatment in children with infantile spasms attending tertiary care hospital at Karachi, Pakistan. METHODS: This is retrospective study of 36 patients out of 94 registered as IS, aged three months to two years, managed and followed up at Aga Khan University Hospital, Karachi, from 2010 to 2015. Data of all children with IS was collected from case record. Details including clinical observations, lab investigations, anti-epileptic medications and treatment outcome was collected and analyzed. Patients who received treatment for six weeks to document response were included. The treatment response was categorized as complete response, partial response (>50% improvement) and no response. Data was analyzed on SPSS using descriptive statistics. RESULTS: Thirty- six patients (38.29%) with IS fulfilled eligibility criteria. The mean ± SD age at presentation was 4.6±2.1 months. Male to female ratio was 2:1. Consanguinity and developmental motor delay was observed in 66.6% and 89% respectively. Symptomatic etiology was predominant (61%) and hypoxic ischemic insult (32%) was the commonest underlying cause. EEG and MRI were diagnostic tools whereas metabolic studies were not helpful. Multiple antiepileptic drugs were used for seizure control and vigabatrin was the most frequently used (88%) drug. Short term treatment response was not different in idiopathic or symptomatic infantile spasms. CONCLUSION: Majority of patients had symptomatic infantile spasms and generalized tonic clonic along with myoclonic jerks were predominant seizure types. EEG and MRI were diagnostic in most of cases. Multiple AEDs were required to control seizures and VGB was most common drug (88%) used. Treatment outcome was not different in idiopathic and symptomatic groups.

MUMPS MYOCARDITIS: A FORGOTTEN DISEASE?

Mumps is an acute viral illness that follows a self-limiting course but up to 10% of cases have a complicated course with the involvement of other organ systems. Myocarditis is reported as a complication but the incidence has greatly fallen ever since the development of the mumps vaccine. A child presented to our department with parotid swelling and fever. Persistent tachycardia with irregular pulse led to further cardiac work up which showed decreased ejection fraction and raised serum cardiac enzymes, indicating myocardial damage. With ionotropic agents and supportive care, there was complete normalization of ejection fraction and serum cardiac enzyme levels. He was discharged within a week of admission. This case highlights the importance of suspecting myocarditis in the setting of mumps, a diagnosis that precludes early suspicion in mumps patients suffering from cardiac symptoms not explained by other potential aetiologies. Early suspicion and timely supportive care are essential to ensure favourable outcomes.

Syndrome of hepatic cirrhosis, dystonia, polycythemia, and hypermanganesemia caused by mutations in SLC30A10, a manganese transporter in man.

Environmental manganese (Mn) toxicity causes an extrapyramidal, parkinsonian-type movement disorder with characteristic magnetic resonance images of Mn accumulation in the basal ganglia. We have recently reported a suspected autosomal recessively inherited syndrome of hepatic cirrhosis, dystonia, polycythemia, and hypermanganesemia in cases without environmental Mn exposure. Whole-genome mapping of two consanguineous families identified SLC30A10 as the affected gene in this inherited type of hypermanganesemia. This gene was subsequently sequenced in eight families, and homozygous sequence changes were identified in all affected individuals. The function of the wild-type protein and the effect of sequence changes were studied in the manganese-sensitive yeast strain Δpmr1. Expressing human wild-type SLC30A10 in the Δpmr1 yeast strain rescued growth in high Mn conditions, confirming its role in Mn transport. The presence of missense (c.266T>C [p.Leu89Pro]) and nonsense (c.585del [p.Thr196Profs(∗)17]) mutations in SLC30A10 failed to restore Mn resistance. Previously, SLC30A10 had been presumed to be a zinc transporter. However, this work has confirmed that SLC30A10 functions as a Mn transporter in humans that, when defective, causes Mn accumulation in liver and brain. This is an important step toward understanding Mn transport and its role in neurodegenerative processes.

Mutation in NSUN2, which encodes an RNA methyltransferase, causes autosomal-recessive intellectual disability.

Causes of autosomal-recessive intellectual disability (ID) have, until very recently, been under researched because of the high degree of genetic heterogeneity. However, now that genome-wide approaches can be applied to single multiplex consanguineous families, the identification of genes harboring disease-causing mutations by autozygosity mapping is expanding rapidly. Here, we have mapped a disease locus in a consanguineous Pakistani family affected by ID and distal myopathy. We genotyped family members on genome-wide SNP microarrays and used the data to determine a single 2.5 Mb homozygosity-by-descent (HBD) locus in region 5p15.32-p15.31; we identified the missense change c.2035G>A (p.Gly679Arg) at a conserved residue within NSUN2. This gene encodes a methyltransferase that catalyzes formation of 5-methylcytosine at C34 of tRNA-leu(CAA) and plays a role in spindle assembly during mitosis as well as chromosome segregation. In mouse brains, we show that NSUN2 localizes to the nucleolus of Purkinje cells in the cerebellum. The effects of the mutation were confirmed by the transfection of wild-type and mutant constructs into cells and subsequent immunohistochemistry. We show that mutation to arginine at this residue causes NSUN2 to fail to localize within the nucleolus. The ID combined with a unique profile of comorbid features presented here makes this an important genetic discovery, and the involvement of NSUN2 highlights the role of RNA methyltransferase in human neurocognitive development.

The upsurge of SSPE--a reflection of national measles immunization status in Pakistan.

Subacute sclerosing panencephalitis (SSPE) is a rare disorder in the developed world. However, an upsurge has been seen lately in our part of the world owing to inadequate measles immunization coverage. At the midst of our struggle against polio, we are struggling with the war against other vaccine-preventable childhood illnesses like measles. The increasing numbers of SSPE that we reported over the past half decade suggest an underlying periodic measles epidemic in Pakistan. In addition, children are now presenting with SSPE in early childhood, warranting a relook, reinforcement and strengthening of primary immunization and mandatory two-dose measles vaccination for all children nationwide. Previously undertaken Measles Supplementary Immunization Activity were a failure in terms of providing the expected cover against measles in young children. Intensive surveillance and establishment of SSPE registers at the district level is essential for eradication of this easily preventable disorder. Unless timely efforts are made to achieve global immunization, SSPE is bound to add to the national disability burden.

Clinical Spectrum, Treatment and Outcome of Children with Autoimmune Encephalitis.

OBJECTIVE: To assess the clinical spectrum, treatment, and outcome of children with autoimmune encephalitis (AE). STUDY DESIGN: Descriptive study. Place and Duration of the Study: Department of Paediatrics, The Aga Khan University Hospital, Karachi, Pakistan, from January 2017 to December 2021. METHODOLOGY: Medical records of children with a diagnosis of AE were reviewed for clinical features, treatment details, and outcomes. Outcome was defined as good (0-2) or poor (3-6) based on a modified Rankin Scale (mRS) score at 3-month follow-up. Descriptive statistics were reported and logistic regression was used to assess the prognostic factors associated with outcome. RESULTS: Thirty-three patients were identified with AE. Thirteen (39.3%) were antibody positive. Anti-N-methyl-D-aspartate receptor (NMDAR) antibody was seen in 92% of positive cases. Behavioural abnormalities (87.8%), seizures (81.8%), movement disorders (66.6%), psychiatric symptoms (63.6%), and mutism (33.3%) were the prominent symptoms. Thirty (91%) patients received first-line immunotherapy. Good outcome was seen in 14 (48.2%) patients. Univariable analysis showed that the odds of having poor outcome were 2.5 (95% confidence interval [CI] 0.37-16.88, p=0.34) in patients with chorea. In addition, an elevated cerebrospinal fluid (CSF) protein had an odds ratio (OR) of 8.6 (CI 0.88-84.83, p=0.064) and positive CSF antibodies had an OR of 3.7 (CI 0.79-17.72, p=0.095) for a poor outcome. Mortality was seen in 4 (12.1%) patients. CONCLUSION: A very low threshold is needed for the diagnosis of AE in children presenting with behavioural symptoms and chorea. Although the odds for poor prognosis were higher in patients with chorea, elevated CSF protein and positive CSF antibodies, the p-value did not come out significant. KEY WORDS: Autoimmune encephalitis, Antibodies, NMDAR, Immunotherapies, mRS score, Outcome.

Prevalence of early childhood disability in a rural district of Sind, Pakistan.

AIM: Children born in low- and mid-income countries are at a high risk of developing disabilities, yet estimates of population-based prevalence are sparse. Our aim was to determine the prevalence of early childhood (0-5 year) disability in Sind, a rural area of Pakistan. METHOD: We conducted a cross-sectional household survey in a population of 25,196 households. The Ten Questions screen and the Signs of Disability in Newborn and Infants screen were used. RESULTS: The disability prevalence in a population of 176,364 individuals was 5.5 out of 1000 in children under 2 years and 5.4 out of 1000 in children aged 2-5 years. Fifty-six per cent were males, and 56% had the disability recognized from birth or soon after. The mortality rate of children aged 0-5 years in the area was estimated as 30 out of 1000 live births. Cerebral palsy was the most common disability identified. The Ten Questions screen had better interrater agreement than the Signs of Disability in Newborn and Infants screen. INTERPRETATION: This is the largest reported household screening survey for early childhood disability at a population level from rural Pakistan. The comparatively low prevalence may be due to the younger age studied and high early childhood mortality. Our data highlight the importance of prospective surveillance at a population level and the need for preventive and support services.

Low glycemic index therapy in children with sub-acute sclerosing panencephalitis (SSPE): an experience from a measles-endemic country.

Introduction: Sub-acute sclerosing panencephalitis (SSPE) is a chronic, progressive neurodegenerative disorder, commonly seen in measles-endemic countries leading to progressive neuronal loss and death. Currently, there is no proven cure for this devastating disease. We started a low glycemic index therapy (LGIT) in children with SSPE using the same principle as per its role in intractable epilepsy. Methodology: Low glycemic index diet was started in children with a confirmed diagnosis of SSPE based on Dyken's criteria. All children were then classified into four stages according to disease progression. The response to diet was evaluated by improvement in their myoclonic jerks, motor activities, and changes in their stage of the disease. Results: A total of 12 children were enrolled. The mean age was 6.65 years (range 3.3-10 years), with a male-to-female ratio of 2:1. Five children were at stage IV, five were at stage III, and two were at stage II at the start of the diet. Nine (75%) children showed improvement in their stage of illness. Of three children who were at stage IV at the initiation of the diet, one improved to stage II and two to stage III. Four children at stage III reverted to stage II. Two children initiated at stage II went into total remission. Seven (58.3%) children showed a >50% reduction in myoclonic jerks with three (25%) having a 100% reduction. Three (25%) children died due to pneumonia. Conclusion: LGIT may play an effective role in the management of SSPE and gives hope to families having children with this potentially life-threatening disease.

Diagnostic dilemmas and challenges in the management of myasthenia in infants and toddlers: A case report.

Myasthenia in the infancy and toddler age group is rare and often presents a challenge to treating pediatric neurologists. Our report addresses the challenges encountered when distinguishing myasthenia in infants and toddlers from similar illnesses, as well as the differentiation between congenital myasthenia, transient myasthenia, and autoimmune myasthenia. We present four cases of myasthenia between the ages of 10 and 30 months. The diagnosis and management of these cases were challenging due to the variability in clinical presentation. Four cases of myasthenia were diagnosed, with three having autoimmune myasthenia and one having congenital myasthenic syndrome. One patient initially tested negative for acetylcholine receptor antibodies, but later tested positive after 4 months and had a rare facial diplegia finding. The patient with congenital myasthenic syndrome had a novel genetic mutation, DPAGT1 homozygous variants, and also had false positive acetylcholine receptor antibodies. These cases highlight the importance of genetic testing for all infants and toddlers suspected of having myasthenia.

Referral Profile of Developmental Disabilities at a Tertiary Care Hospital in a Resource-limited Country.

The burden and the spectrum of neuro-developmental disabilities are well-established in the developed countries, however, they continue to be a challenge in the Low Middle-Income Countries. The aim of this study was to present the referral profile and trends of developmental disabilities in the child development centre of The Agha khan University, from 2012 to 2021. All children (1 month to 18 years), who had undergone diagnostic evaluations for suspected neurodevelopmental disabilities were included. A total of 1340 children were evaluated at the centre. The mean age of the children at the presentation was 5.4 ± 3.0 years. Male to female ratio was 3:1. Autism Spectrum Disorder (ASD) was the most common diagnosis (n=446, 33.3%). This study highlights a considerable burden and an increasing trend of children being referred for suspected developmental disabilities in Pakistan. Key Words: Developmental disabilities, Referral, Pakistan, Autism spectrum disorder.

Spectrum of Common Pediatric Neurological Disorders: A Cross-Sectional Study From Three Tertiary Care Centres Across Pakistan.

BACKGROUND: There is dearth of information on the spectrum of neurological disorders among children less than 18 years of age. The aim of this study is to identify the commonly presenting neurological disorders among children aged ≤ 18 years in Pakistan. METHODS: We conducted a cross-sectional study at three tertiary care hospitals in Pakistan. RESULTS: A total of 17,176 children were included in our study; 61.8% were boys and 38.2% females. The most commonly presenting neurological disorder was epilepsy (36%), followed by behavior disorders (16%) and cerebral palsy (10.5%). There was significant difference between children less than 5 years and greater than 5 years age groups, with less than 5 years age group showing higher prevalence for behavioral disorders (P < 0.001), cerebral palsy (P < 0.001), infections (P = 0.014), sequalae (P < 0.001), and developmental disorders (P < 0.001). Gender-wise distribution showed epilepsy to be the most common neurological disorder among both genders, with a significant difference being reported between gender and epilepsy (P = 0.009), headache disorders (P < 0.001), neuroinflammatory disorders (P = 0.025), neurocutaneous syndromes (P < 0.001), behavioral diseases (P < 0.001), cerebral palsy (P = 0.009), and movement disorders (P < 0.001). CONCLUSIONS: The result of this analysis helps to assess the commonly presenting neurological disorders in children. This study will help health care workers in resource-poor settings within Pakistan to be mindful of the common neurological disorders while diagnosing a child with neurological symptoms in an outpatient setting. Health care providers need to be trained to identify and treat these common conditions; however, there is still a dire need for more trained neurologists across the country.

Gain and loss of function variants in EZH1 disrupt neurogenesis and cause dominant and recessive neurodevelopmental disorders.

Genetic variants in chromatin regulators are frequently found in neurodevelopmental disorders, but their effect in disease etiology is rarely determined. Here, we uncover and functionally define pathogenic variants in the chromatin modifier EZH1 as the cause of dominant and recessive neurodevelopmental disorders in 19 individuals. EZH1 encodes one of the two alternative histone H3 lysine 27 methyltransferases of the PRC2 complex. Unlike the other PRC2 subunits, which are involved in cancers and developmental syndromes, the implication of EZH1 in human development and disease is largely unknown. Using cellular and biochemical studies, we demonstrate that recessive variants impair EZH1 expression causing loss of function effects, while dominant variants are missense mutations that affect evolutionarily conserved aminoacids, likely impacting EZH1 structure or function. Accordingly, we found increased methyltransferase activity leading to gain of function of two EZH1 missense variants. Furthermore, we show that EZH1 is necessary and sufficient for differentiation of neural progenitor cells in the developing chick embryo neural tube. Finally, using human pluripotent stem cell-derived neural cultures and forebrain organoids, we demonstrate that EZH1 variants perturb cortical neuron differentiation. Overall, our work reveals a critical role of EZH1 in neurogenesis regulation and provides molecular diagnosis for previously undefined neurodevelopmental disorders.

Spinal muscular atrophy: clinical spectrum and genetic mutations in Pakistani children.

BACKGROUND: In Pakistan the rate of consanguineous marriages is high, thus, the chance of incidence of autosomal recessive disorders is likely to be high. The aim of this study is to investigate the clinical characteristics and genetics of spinal muscular atrophy (SMA) in children who presented to Aga Khan University, Karachi. MATERIALS AND METHODS: This study was a retrospective review of the medical charts of children (neonate: 15 years) with discharge diagnosis of SMA during last 10 years. Demographic features, consanguinity, and diagnostic analysis (including genetic analysis) were noted. RESULTS: During the study period 67 children had a discharge diagnosis of SMA. Werdnig Hoffman disease (SMA type I) was the commonest variant seen in 37 (56%) children. Overall 68% were infants. High parental consanguinity was observed in 68% of the study cohort. The history of delayed development and undiagnosed early death was observed in the families of 19 children. Genetic testing was performed in 22 (33%) children. Survival motor neuron (SMN) 1 gene deletion was found in 19 (86%) of the 22 patients in whom the gene analysis was done and 13 (68%) were also positive for neuronal apoptosis inhibitory proteins (NAIP) deletion. CONCLUSION: SMA is not an uncommon neurodegenerative disorder in Pakistan and SMA type I was the most common type. SMN1 gene deletion was the most common genetic deletion found in this study. In addition, family history of developmental delay and frequent early deaths highlights the need for implementation of prenatal diagnosis for early detection, effective control, and management of this disorder in Pakistan.