Global Developmental Delay Research Articles

Two familial cases of infantile epileptic spasms syndrome associated with UDP-glucose-6-dehydrogenase deficiency.

Developmental and epileptic encephalopathies (DEEs) are severe forms of epilepsy characterized by seizure onset in infancy or childhood. The seizures are typically drug-resistant and often accompanied by significant alterations in the electroencephalogram (EEG). DEEs are associated with neurodevelopmental impairment, which can arise from both the epileptic activity itself and the underlying etiology, which is most often genetic in origin. We present the clinical and molecular features of two patients with DEE associated with a pathogenic variant in the UGDH gene. This gene encodes a protein that converts uridine diphosphate (UDP)-glucose into UDP-glucuronate, which plays a crucial role in the biosynthesis of glycosaminoglycans, essential components of the connective tissue and extracellular matrix. Both patients started with epileptic spasms associated with a pattern of hypsarrhythmia in the EEG at 4 months of age. Both developed global developmental delay and the physical examination revealed hypotonia and mildly dysmorphic features. In both families, there was another affected sibling with a similar clinical presentation, although genetic studies were not performed in one of these children. A homozygous pathogenic variant in the UGDH gene, NM_003359.4:c.131C>T - p.(Ala44Val), previously reported to be associated with the described phenotype, was identified.

28 Vaccination experiences for children with special needs - An examination of the impact of behaviours on vaccine uptake

Abstract Background While vaccines have been one of the most effective medical interventions to reduce the morbidity and mortality of many communicable illnesses, many factors have led to suboptimal immunization rates amongst paediatric patients. One of which that has not been explored widely in research literature is the impact of maladaptive behaviours on annual immunization rates. Behaviours such as aggression, agitation and flight are common amongst children with a neurodevelopmental diagnosis such as autism spectrum disorder, global developmental delay, and intellectual delay. When children are young, physical restraints by parents are often the method used to aid in the administration of the vaccine. However, as they age physical restraints is often regarded as inappropriate. Objectives The purpose of this study is to determine the extent in which disruptive behaviours (aggression, agitation and flight) affect annual vaccination rates for children with a neurodevelopmental diagnosis above the age of 6 years where physical restraining for vaccinations is no longer deemed appropriate or safe. Design/Methods Families with children diagnosed with Autism Spectrum Disorder (ASD), Intellectual Disorder (ID), and/or Global Developmental Delay (GDD) aged 6-17 years, seen through outpatient clinics at the Ron Joyce Children’s Health Centre of McMaster Children’s hospital in Hamilton between November 2022 – April 2023 were invited to participate in this cross sectional survey. The study aimed to capture both quantitative data on vaccine uptake and qualitative data on how vaccination experiences could be improved for children with neurodiversity. Results A total of 109 participants completed the survey. Among them, forty-three (39%) participants had a diagnosis of ASD and sixty-six (51.2%) had a diagnosis of global developmental delay or intellectual disability. Forty-six (45.6%) and 82 (76%) did not receive the Covid-19 and the influenza vaccination respectively. Of the children that did not receive the CoVid-19 vaccine, fourteen (30%) of the families had brought their child to be vaccinated, but the health care team could not administer the vaccine due to their child’s behaviours and twenty-one (37%) of the families anticipated that the vaccination would be a difficult experience because of their child’s behaviours and did not bring their child to get vaccinated. Of the children that did not receive the influenza vaccine, fifteen (18%) families had brought their child to be vaccinated, but the health care team could not administer the vaccine due to the child’s behaviours and 42 (50%) families anticipated that the vaccination would be a difficult experience because of their child’s behaviours and did not bring their child to get vaccinated. The main themes that emerged from the studies on ways to improve the vaccination experience for families include administering the vaccine in a low sensory environment, decreasing wait time, and ensuring clinic staff have experience in caring for children with special needs. Conclusion Children with special needs are a vulnerable population warranting concerted effort to ensure equitable access to immunizations. Interventions such as clinics specifically designed for children with neurodiversity should be implemented with the hope to further improve immunization rates within this population.

66 Survival and school-age outcomes of extremely premature neonates with intraventricular hemorrhage

Abstract Background Extremely low gestational age (ELGA) neonates are at risk for intraventricular hemorrhage (IVH) and periventricular hemorrhagic infarction (PVHI). There is no clear consensus on the prognosis of these conditions. Objectives The aim of this study was to compare the survival, and the neurodevelopmental outcomes (NDO) at school-age for neonates with IVH and/or PVHI, to those without. Design/Methods This retrospective single-center study (2012-2017) included neonates less than 26 weeks gestational age (GA) who received resuscitation and early intensive care. Imaging data were collected from cranial US for the presence of IVH described by Papile grading. Survival was defined as survival to discharge. NDO were classified as no neurodevelopmental impairment (NDI), no NDI with multidisciplinary referrals, and the adverse outcome was defined as NDI at school-age. NDI included any diagnosis of cerebral palsy, global developmental delay, intellectual disability, visual or hearing impairment. Autism spectrum disorder (ASD) was included as an outcome of interest. Results 164 infants met inclusion criteria, of whom 156 survived resuscitation. Mean GA was 24 weeks and 6 days (SD 6 days) and mean birth weight 701g (SD 125g), grade I-II IVH was present in 43 (28%) infants, and grade III-IV IVH was present in 48 (31%) infants. Survival was 45% for those with bilateral grade III-IV IVH, 53% for unilateral grade III-IV IVH, 78% for bilateral grade I-II IVH, 80% for unilateral grade I-II IVH, and 81% for no IVH groups. 108 infants survived to discharge and 90 had complete follow up at school age. 30% of children had NDI and ASD was diagnosed in 12%. Logistic regression for adverse outcome demonstrated an adjusted odds-ratio (OR) 0.30 (95% CI 0.14, 0.56) for gestational age (p <0.001). The logistic regression resulted in adjusted OR 0.72 (95% CI 0.21, 2.37) for grade I-II IVH and OR 1.43 (95% CI 0.4, 5.03) for Grade III-IV IVH (p=0.63). Conclusion In neonates born ELGA, survival decreased with increasing severity of IVH. Decreasing GA, but not severity of IVH, was predictive of neurodevelopmental impairment. Extremely preterm infants born < 26 weeks are at high risk of NDI and of ASD.

Nephrocalcinosis, distal renal tubular acidosis and skeletal abnormality in two siblings with ROGDI-related Kohlschütter-Tönz syndrome.

Kohlschütter-Tönz (KTS) is a rare autosomal recessive, genetically heterogeneous disorder characterized by a triad of early-onset seizures, global developmental delay or regression, and amelogenesis imperfecta of both temporary and permanent teeth. To date, 66 cases have been reported in the literature, of which 44 with genetic confirmation. Here we report the observation of sibling pairs in a family from a small village in India who presented with nephrocalcinosis, distal renal tubular acidosis, and skeletal abnormality. Nephrocalcinosis has only been reported once before in an individual affected with KTS. Trio exome sequencing revealed a novel, homozygous, likely pathogenic variant, c.646-2_649del, in exon 9 of the ROGDI gene (NM_024589.3) in the first child. Sanger sequencing confirmed homozygosity in both children. Both parents are heterozygous carriers of the same variant. Further research needs to be done to identify the exact mechanism by which ROGDI-encoded protein deficiency leads to nephrocalcinosis and distal renal tubular acidosis.

Diagnostic Approach to Children with Unexplained Global Developmental Delay in Pediatric Neurology Outpatient Clinic.

Global developmental delay (GDD) is a common pediatric disorder that affects up to 3% of children. Due to the heterogeneous etiology of GDD, diagnostic procedures and algorithms are complex and diverse. The aim of our study was to investigate the diagnostic yield of genetic, metabolic, and imaging studies in establishing the etiology of unexplained GDD (UGDD). In this retrospectively observational study, we examined the medical records of all children diagnosed with UGDD at the Department of Pediatric Neurology, University Medical Centre Ljubljana, Slovenia, between January and December 2019. We evaluated the effectiveness of various genetic, metabolic, and magnetic resonance imaging (MRI) tests in identifying the underlying cause of GDD. Additionally, we assessed subgroups of patients to determine whether any of the studied tests were particularly beneficial based on their clinical symptoms. A total of 123 patients met the inclusion criteria, with a median age of 4.3 years (range, 0-16 years), of which 71 (57.7%) were males. Genetic diagnosis was established in 47.1% (58/123) of patients. Metabolic laboratory testing did not identify a metabolic disease in any of the tested participants (114/123) and MRI was critical for diagnosis in only 1/81 (1.2%) patient. Our findings strongly suggest that genetic testing surpasses MRI and metabolic testing in establishing the etiology of UGDD in a pediatric neurology outpatient setting. This information will help guide the diagnostic evaluation of these children.

Early Maternal Prenatal Cannabis Use and Child Developmental Delays

Maternal prenatal cannabis use is associated with adverse neonatal health effects, yet little is known about its association with child developmental outcomes. To evaluate associations between maternal prenatal cannabis use in early pregnancy and child early developmental delays. This cohort study included 119 976 children born to 106 240 unique individuals between January 2015 and December 2019 and followed up to aged 5.5 years or younger (through December 31, 2021) at Kaiser Permanente Northern California. Individuals were screened for prenatal cannabis use via self-report and urine toxicology at entrance into prenatal care (approximately 8- to 10-weeks' gestation). Data were analyzed from February 2023 to March 2024. Maternal prenatal cannabis use defined as any use (self-reported or by urine toxicology testing) and use frequency. Early developmental delays (speech and language disorders, motor delays, global delays) in children up to age 5.5 years defined by International Statistical Classification of Diseases and Related Health Problems, Ninth Revision and Tenth Revision diagnoses codes ascertained from electronic health records. In this cohort of 119 976 pregnancies among 106 240 unique pregnant individuals, there were 29 543 Hispanic pregnancies (24.6%), 6567 non-Hispanic Black pregnancies (5.5%), 46 823 non-Hispanic White pregnancies (39.0%), 12 837 pregnancies (10.7%) to individuals aged 24 years or younger, and 10 365 pregnancies (8.6%) to individuals insured by Medicaid. Maternal prenatal cannabis use was documented for 6778 pregnancies (5.6%). Daily maternal prenatal cannabis use was reported for 618 pregnancies (0.5%), weekly for 722 pregnancies (0.6%), and monthly or less for 1617 pregnancies (1.3%). No association was observed between maternal prenatal cannabis use and child speech and language disorders (HR, 0.93; 95% CI, 0.84-1.03), global developmental delays (HR, 1.04; 95% CI, 0.68-1.59), or motor delays (HR, 0.86; 95% CI, 0.69-1.06). No association was detected between the frequency of maternal prenatal cannabis use and child early developmental delays. In this cohort study, maternal prenatal cannabis use was not associated with an increased risk of child early developmental delays. Future research is needed to assess different patterns of cannabis use throughout pregnancy. Given the association between maternal prenatal cannabis use and other adverse outcomes, pregnant individuals should be educated on those risks.

Clinical and genetic characterisation of childhood-onset sensorineural hearing loss reveal associated phenotypes and enrichment of pathogenic founder mutations in the Finnish population

Objective To examine the clinical and genetic characteristics of childhood-onset bilateral sensorineural hearing loss (SNHL) in Finland. Design Retrospective analysis. Study sample A total of 249 children younger than 18 years were diagnosed with bilateral SNHL in Oulu University Hospital, Finland, from 2017 to 2022. Results Pathogenic or likely pathogenic gene variants or chromosome abnormalities explaining SNHL were identified in 41% (N = 101/249) of children. Likely causative variants were more commonly identified in patients with severe SNHL than in those with moderate or mild SNHL. Our study identified likely causative gene variants in 24 different genes and six different likely causative chromosome abnormalities, demonstrating the genetic heterogeneity of SNHL. Population-enriched founder mutations were identified in the CABP2, CLRN1, MYO7A, SUCLA2, TMC1, and TWNK genes. A significant number of patients had associated phenotypes, including global developmental delay or intellectual disability (16%), language disorder (20%), ophthalmological abnormalities (16%), or malformations other than those involving the ear (10%). Conclusions SNHL is genetically and clinically heterogeneous. Pathogenic variants in GJB2 were the most common. Several population-enriched variants were identified as causing SNHL in the northern Finnish population. Associated medical phenotypes are common and should be taken into account in patients’ follow-up and treatment.

Simultaneous Infantile Spasms and Focal Seizures: A Rarely Reported Combined Seizure Phenomenon on Video Electroencephalogram (VEEG).

Focal seizures (FS) have previously been described before or after infantile spasm (IS) clusters, but FS occurring simultaneously with an IS cluster has been rarely reported in the EEG literature. We present three cases where focal seizures (FS) occurred concurrently during an infantile spasm (IS) cluster on VEEG. On VEEG, onset of IS cluster preceded FS in all three patients; however, patient three was diagnosed with FS prior to the onset of IS. FS duration ranged from 10-90 s and was electrographic-only in two out of the three patients. Unfortunately, the first two patients are now deceased, and for patient two no etiology was ever identified. Currently, patient three is free of spasms as well as seizures but has global developmental delay; no definite etiology has been identified for their presentation. Concurrent FS with IS suggests that the seizure types may be generated in different brain areas with one seizure type potentially triggering the other and is generally reflective of multifocal or diffuse cerebral disease with a poor prognosis as was seen in at least two of our patients. Our three cases of IS where FS occurred concurrently contribute to the limited existing data describing this phenomenon on VEEG.

A novel loss-of-function KCNB1 gene variant in a twin with global developmental delay and seizures.

Human voltage-gated potassium (Kv) channels are expressed by a 40-member gene family that is essential for normal electrical activity and is closely linked to various excitability disorders. Function-altering sequence variants in the KCNB1 gene, which encodes the neuronally expressed Kv2.1 channel, are associated with neurodevelopmental disorders including developmental delay with or without epileptic activity. In this study, we describe a 40-month-old fraternal twin who presented with severe neurodevelopmental delay. Electroencephalogram recordings at 19 months of age revealed poor sleep architecture and the presence of multifocal epileptiform discharges. The individual's fraternal twin was neurotypical, and there was no family history of neurodevelopmental delay or seizures. Whole genome sequencing at 33 months of age for the proband revealed a de novo variant in KCNB1 [c.1154C > T/p.Pro385Leu], encoding a proline-to-leucine substitution at residue 385, in the extracellular region immediately preceding Kv2.1 transmembrane segment 6 (S6). Cellular electrophysiological analysis of the effects of the gene variant in heterologously expressed Kv2.1 demonstrated that homozygous Kv2.1-P385L channels were completely non-functional. Channels generated by a 50/50 expression of wild-type Kv2.1 and Kv2.1-P385L, designed to mimic the proband's heterozygous status, revealed a partially dominant-negative effect, resulting in an 81% reduction in current magnitude. The dramatic loss of function in Kv2.1 is the most likely cause of the severe developmental delay and seizure activity in the proband, further enriching our phenotypic understanding of KCNB1 developmental encephalopathies.

Cohen Syndrome, A Case Report

Background: Cohen syndrome is a rare genetic disorder characterized by physical, developmental, and intellectual disabilities. It is primarily considered in children presenting with microcephaly, early-onset hypotonia, neutropenia, and global developmental delay. Results: A 16-day-old female infant with low birth weight and dysmorphic features was evaluated. This case highlights the importance of considering Cohen syndrome in the differential diagnosis of infants with similar clinical findings. Early recognition allows for timely intervention and support. Conclusion: While there is no cure for Cohen syndrome, early diagnosis and management can improve quality of life.Genetic counseling is essential for affected families.

Response to therapy of creatine transporter deficiency caused by a hypomorphic variant in SLC6A8

Cerebral creatine deficiency syndromes (CCDS) are rare inherited metabolic disorders caused by defective biosynthesis or transport of creatine. These conditions are characterized by reduced accumulation of creatine in the brain, mild to severe intellectual disability, global developmental delay, and speech-language disorders. The amount of brain creatine reduction needed to cause symptoms is not known. Here we report a new patient with creatine transporter deficiency (CTD) who presented at 15 months of age with seizures and global delays with no speech at 3 years of age. Brain MRI was normal, but brain MRS indicated creatine levels reduced to about 20 % of normal. He had normal levels of creatine and guanidinoacetate in plasma, but increased creatine/creatinine ratio in urine. DNA sequencing identified a hemizygous c.832C > T (p.Arg278Cys) variant in the creatine transporter gene SLC6A8. Fibroblasts from this patient had about 25 % of normal creatine transport activity, a value much higher than that measured in patients whose variants introduced premature stop codons in SLC6A8. The child was started on supplements of creatine, glycine, and arginine. His speech improved dramatically, and he had no more seizures, even during episodes of fever. Despite the clinical improvement, a repeat MRS demonstrated similar levels of brain creatine. This study suggests that a reduction in creatine transporter activity to 25 % or less is sufficient to cause symptoms of brain creatine deficiency and that functionally milder forms of CTD might respond to supplements aimed at replenishing brain creatine.

Whole Exome Sequencing and Panel-Based Analysis in 176 Spanish Children with Neurodevelopmental Disorders: Focus on Autism Spectrum Disorder and/or Intellectual Disability/Global Developmental Delay

Background: Neurodevelopmental disorders (NDDs) represent a significant challenge in pediatric genetics, often requiring advanced diagnostic tools for the accurate identification of genetic variants. Objectives: To determine the diagnostic yield of whole exome sequencing (WES) with targeted gene panels in children with neurodevelopmental disorders (NDDs). Methods: This observational, prospective study included a total of 176 Spanish-speaking pediatric patients with neurodevelopmental disorders (NDDs), encompassing intellectual disability (ID), global developmental delay (GDD), and/or autism spectrum disorder (ASD). Participants were recruited from January 2019 to January 2023 at a University Hospital in Madrid, Spain. Clinical and sociodemographic variables were recorded, along with genetic study results. The age range of the subjects was 9 months to 16 years, and the percentage of males was 72.1%. The diagnostic yield of whole exome sequencing (WES) was calculated both before and after parental testing via Sanger DNA sequencing. Results: The study included 176 children: 67 (38.1%) with ID, 62 (35.2%) with ASD, and 47 (26.7%) with ASD + ID. The diagnostic yield of proband-only exome sequencing was 12.5% (22/176). By group, the diagnostic yield of proband-only exome sequencing was 3.2% in the ASD, 12.7% in the ASD + ID, and 20.8% in the ID group. Variants of uncertain significance (VUS) were found in 39.8% (70/176). After parental testing, some variants were reclassified as “likely pathogenic”, increasing the diagnostic yield by 4.6%, with an overall diagnostic yield of 17.1%. Diagnostic yield was higher in patients with syndromic ID (70.6%% vs. 29.4%; p = 0.036). Conclusions: A sequential approach utilizing WES followed by panel-based analysis, starting with the index case and, when appropriate, including the parents, proves to be a cost-effective strategy. WES is particularly suitable for complex conditions, as it allows for the identification of potentially causative genes beyond those covered by targeted panels, providing a more comprehensive analysis. Including parental testing enhances the diagnostic yield and improves accuracy, especially in cases with variants of uncertain significance (VUS), thereby advancing our understanding of NDDs.

The application of whole-exome sequencing in the early diagnosis of rare genetic diseases in children: a study from Southeastern China.

Genetic diseases exhibit significant clinical and genetic diversity, leading to a complex and challenging diagnostic process. Exploiting novel approaches is imperative for the molecular diagnosis of genetic diseases. In this study, we utilized whole-exome sequencing (WES) to facilitate early diagnosis in patients suspected of genetic disorders. This retrospective analysis included 144 patients diagnosed by singleton-WES Trio-WES between January 2021 and December 2023. We investigated the relevance of diagnosis rates with age, clinical presentation, and sample type. Among the 144 patients, 61 were diagnosed, yielding an overall diagnostic rate of 42.36%, with Trio-WES demonstrating a significantly higher diagnostic rate of 51.43% (36/70) compared to singleton-WES at 33.78% (25/74) (p < 0.05). Global developmental delay had a diagnosis rate of 67.39%, significantly higher than muscular hypotonia at 30.43% (p < 0.01) among different clinical phenotypic groups. Autosomal dominant disorders accounted for 70.49% (43/61) of positive cases, with autosomal abnormalities being fivefold more prevalent than sex chromosome abnormalities. Notably, sex chromosome abnormalities were more prevalent in males (80%, 8/10). Furthermore, 80.56% (29/36) of pathogenic variants were identified as de novo mutations through Trio-WES. These findings highlight the effectiveness of WES in identifying genetic variants, and elucidating the molecular basis of genetic diseases, ultimately enabling early diagnosis in affected children.

A novel variant in the 3′ UTR of the TCF4 gene likely causes Pitt-Hopkins syndrome: a case report

BackgroundPitt–Hopkins syndrome (PTHS) is a rare neurodevelopmental disorder that results from variants of TCF4 gene. PTHS follows an autosomal dominant inheritance pattern and the underlying pathological mechanisms of this disease are still unclear.MethodsWhole-genome sequencing (WGS) was conducted to screen for potential pathogenic variant in a boy highly suspected of having a genetic disorder. PCR and Sanger sequencing were used to verify the effects of the variant. Serum TCF4 levels were measured by ELISA.ResultsWe present a 4-year and 3-month-old Chinese boy clinically and molecularly diagnosed with PTHS. The proband experienced global development delay, and the preliminary clinical diagnosis was cerebral palsy. WGS identified a de novo heterozygous variant: c.*1A > G in the 3’UTR of the TCF4 gene as a potential cause of his condition. The variant was verified to cause aberrant mRNA splicing by PCR and the aberrant splicing was confirmed by Sanger sequencing.ConclusionThe study identified and demonstrated the pathogenicity of a novel 3’UTR site TCF4 variant for the first time. This research enhances understanding of pathogenetic mechanisms of PTHS and aids genetic counseling and diagnosis.

7308 A Case of Thyroid Hormone Resistance Associated With a Novel Mutation in the THRA Gene

Abstract Disclosure: J.A. Siddiqui: None. M. Barbosa: None. V. Fettig: None. C.J. Romero: None. Introduction: Thyroid hormone resistance (THR) is a syndrome leading to decreased response of target organs to thyroid hormone. Normal thyroid hormone action is mediated by thyroid hormone nuclear receptors and is essential for normal development and metabolism. Two isoforms are encoded by the thyroid hormone receptor α and β genes (THRA and THRB). Mutations in THRB are commonly reported with limited cases of THRA mutations. We report a 15-month-old and her mother with a pathogenic variant in the THRα receptor leading to thyroid hormone resistance. CASE: A 15-month-old ex-39-week gestation female was born small for gestational age (birth weight: 2450 grams,3rd %ile and birth length: 17 inches,1st %ile). The newborn screen was normal. She presented with macroglossia, low tone and global developmental delay. She had severe constipation complicated by rectal prolapse that required surgical correction. There are multiple relatives (mother, maternal half-brother and maternal grandparents) with neurodevelopmental issues. The mother’s previous genetic evaluation was non-diagnostic. Mother reports a thyroid condition but without treatment. The patient was initially referred to genetics and whole exome sequencing revealed a heterozygous c.1205 T&amp;gt;C p. (L402P) variant in the THRα gene, which was maternally inherited and reported as a variant of uncertain significance. On physical exam, Heart rate was 112 bpm; height &amp;lt;1%ile (Z-score -3.22 SD), weight 3%ile (Z-score -1.89 SD). Patient has a wide anterior fontanelle (4x3 cm), macroglossia and delayed teeth eruption. Other exam findings: non-palpable thyroid and postaxial polydactyly on the 5th digit of the right toe. Thyroid hormone testing: normal TSH 1.829 uIU/mL, low total T4 4.4 mcg/dL, low Free T4 of 0.58 ng/dL and high free T3 of 4.24 pg/mL. Levothyroxine treatment was initiated(25 mcg daily). After 1 month treatment, TSH level was 0.23 uIU/mL, total T4 was 6.1 mcg/dL and low reverse T3 of 5.8 ng/dL. DISCUSSION: Thyroid hormone resistance due to THRα mutations are rare and under-recognized. The main clinical phenotype includes growth retardation, delayed development, decreased muscle tone, delayed tooth eruption and constipation. Unlike patients with THRβ mutations, the hypothalamus-pituitary-thyroid axis in patients with THRα mutations is minimally affected with a normal TSH level. Total T3 levels are elevated with slightly low total T4 and free T4:T3 ratio is low. Treatment with levothyroxine leads to suppressions of TSH levels, therefore confirming intact central T3 feedback loop. Reports, however, show minor clinical improvements with treatment; therefore further research is needed in these patients to explore more effective therapeutic options. We present a case of a novel congenital THRA mutation leading to a clinical phenotype consistent with THR. She continues care in our clinic with hopes to further study her mutation. Presentation: 6/2/2024

7494 Glycerol Phenylbutyrate Treatment of Two Patients with Monocarboxylate Transporter 8 Deficiency

Abstract Disclosure: A. Zung: None. N. Sonntag: None. U. Schweizer: None. E. Banne: None. D. Braun: None. Context: Monocarboxylate transporter 8 (MCT8) deficiency is a rare genetic disease that leads to severe global developmental delay. MCT8 facilitates thyroid hormone (TH) transport across the cell membrane, and the serum TH profile is characterized by high T3 and low T4 levels. Currently, the two thyromimetic agents 3,5-diiodothyropropionic acid (DITPA) and triiodothyroacetic acid (TRIAC) have been evaluated in the treatment of these patients, as they both partially restore intracellular TH action independent of MCT8. Recent studies have shown that the chemical chaperone sodium phenylbutyrate (NaPB) restored mutant MCT8 function and increased TH content in patient-derived induced pluripotent stem cells, making it a potential treatment for MCT8 deficiency. Objective: We aimed to assess the efficacy and safety of glycerol phenylbutyrate (GPB) in MCT8 deficiency. Methods: We treated two monozygotic twins aged 14.5 years with MCT8 deficiency due to P321L mutation with escalating doses of GPB over 13 months. We recorded TH, serum markers of peripheral hyperthyroidism, vital signs, anthropometric measurements and neurocognitive functions by several neurodevelopment validated tests. Resting metabolic rate (RMR) was measured by indirect calorimetry. Serum metabolites of GPB were monitored as a safety measure. In-vitro effects of NaPB were evaluated in MDCK1 cells stably expressing the MCT8P32[1]L mutation. Results: NaPB restored mutant MCT8 expression in MDCK1 cells and increased T3 transport into cells carrying the P321L mutation. GPB treatment yielded a dose-dependent decrease in FT3 and an increase in FT4 serum levels. The patients showed an elevation in cholesterol levels in parallel with GPB dose, but sex-hormone binding protein (SHBG), another marker of peripheral hyperthyroidism was not affected. The patients showed a significant weight gain simultaneously with a reduction in RMR. Only minor neuro-cognitive improvement was observed, mainly in hyperreflexia score, slight improvement in gross motor functions and a mild progression in cognitive functions. Serum metabolites of GPB did not exceed the toxic range but elevated liver transaminases restricted the dose intensification of GPB. Conclusions: In the first report of GPB treatment in MCT8 deficiency patients we found an improvement in TH profile and body-mass index (BMI). The reduction in T3 levels could contribute to the remarkable increase in BMI-SDS, since various aspects of peripheral hyperthyroidism in MCT8 deficiency, including poor weight gain, were attributed to elevated T3. The limited effects of GPB treatment on cognitive and motor functions can derive from the advanced age of the patients at the time of the intervention. Presentation: 6/2/2024

UBTF haploinsufficiency associated with UBTF-related global developmental delay and distinctive facial features without neuroregression

BackgroundThe Upstream Binding Transcription Factor (UBTF) gene encodes two nucleolar proteins, UBTF1 and UBTF2. UBTF1 regulates rRNA transcription by RNA polymerase I, while UBTF2 regulates mRNA transcription by RNA polymerase...

Pre-clinical development of AP4B1 gene replacement therapy for hereditary spastic paraplegia type 47.

Spastic paraplegia 47 (SPG47) is a neurological disorder caused by mutations in the adaptor protein complex 4 β1 subunit (AP4B1) gene leading to AP-4 complex deficiency. SPG47 is characterised by progressive spastic paraplegia, global developmental delay, intellectual disability and epilepsy. Gene therapy aimed at restoring functional AP4B1 protein levels is a rational therapeutic strategy to ameliorate the disease phenotype. Here we report that a single delivery of adeno-associated virus serotype 9 expressing hAP4B1 (AAV9/hAP4B1) into the cisterna magna leads to widespread gene transfer and restoration of various hallmarks of disease, including AP-4 cargo (ATG9A) mislocalisation, calbindin-positive spheroids in the deep cerebellar nuclei, anatomical brain defects and motor dysfunction, in an SPG47 mouse model. Furthermore, AAV9/hAP4B1-based gene therapy demonstrated a restoration of plasma neurofilament light (NfL) levels of treated mice. Encouraged by these preclinical proof-of-concept data, we conducted IND-enabling studies, including immunogenicity and GLP non-human primate (NHP) toxicology studies. Importantly, NHP safety and biodistribution study revealed no significant adverse events associated with the therapeutic intervention. These findings provide evidence of both therapeutic efficacy and safety, establishing a robust basis for the pursuit of an IND application for clinical trials targeting SPG47 patients.

Inherited PURA Pathogenic Variant Associated With a Mild Neurodevelopmental Disorder.

Purine-rich element-binding protein alpha (PURA) regulates gene expression and is ubiquitously expressed with an enrichment in neural tissues. Pathogenic variants in PURA cause the neurodevelopmental disorder PURA syndrome that has a variable phenotype but typically comprises moderate-to-severe global developmental delay, intellectual disability, early-onset hypotonia and hypothermia, epilepsy, feeding difficulties, movement disorders, and subtle facial dysmorphism. Speech is reportedly absent in most, but the specific linguistic phenotype is not well described. We used genome sequencing to identify a pathogenic gene variant as part of a study of children ascertained for severe primary speech disorder in the absence of moderate or severe ID. The novel PURA c.296G>T (p.Arg99Leu) pathogenic missense variant segregated in the female proband and her affected mother. The proband had dysarthria; phonological disorder; and severe receptive and expressive language impairment, borderline intellect, attention difficulties, oropharyngeal dysmotility, and dysmorphic facial features. Her mother had dysarthria, moderate receptive language impairment, and borderline intellect. Both the proband and her mother completed mainstream schooling with classroom support. This is the first inherited PURA pathogenic germline variant in over 600 unrelated families documented on ClinVar or reported in the literature. PURA testing should be considered in families with primary speech disorder and borderline intellectual disability, given the specific genetic counseling implications.

Advancements in the Study of Clinical Features and Molecular Functions in Heterogeneous TAF1-associated Clinical Phenotypes

Purpose of review: TATA-binding protein (TBP)-associated factor 1 (TAF1) encodes the largest component of the transcription factor IID (TFIID) complex, which binds to core promoters and serves as a scaffold for assembly of the RNA polymerase II transcription complex. Variants in TAF1 are associated with X-linked dystonia-parkinsonism (XDP) and X-linked syndromic mental retardation-33 (MRXS33). This review provides a concise summary of the genetic and clinicopathological features of TAF1 variants related to phenotype. Recent findings: XDP is an adult-onset X-linked progressive neurodegenerative disorder presenting dystonia and parkinsonism and caused by a SINE-VNTR-Alu (SVA)-type retrotransposon within TAF1. TAF1/MRXS33 intellectual disability syndrome is characterized by global developmental delay, intellectual disability, facial dysmorphia, generalized hypotonia, and neurological abnormalities due to the missense variants in TAF1. Various symptoms of TAF1 missense mutations may be related to mutations in different functional regions of the protein. The clinical manifestations of XDP and MRXS33, both caused by variants of TAF1, present prominent heterogeneity, which could be influenced by whether the TAF1 mutation is located in the coding region, the time when TAF1 expression decreases, and the effect on downstream gene expression. Summary: TAF1 is linked to many different phenotypes because of its variable regulation of coding and noncoding elements, which makes its mechanistic roles in disease challenging to interpret. However, it is important to note that strategies to correct TAF1 splicing could provide therapeutic benefits in different diseases.