Concurrent de novo MACF1 mutation and inherited 16p13.11 microduplication in a preterm newborn with hypotonia, joint hyperlaxity and multiple congenital malformations: a case report.

BACKGROUND: The MACF1 gene, found on chromosome 1p34.3, is vital for controlling cytoskeleton dynamics, cell movement, growth, and differentiation. It consists of 101 exons, spanning over 270 kb. The 16p13.11 microduplication syndrome results from the duplication of 16p13.11 chromosome copies and is associated with various neurodevelopmental and physiological abnormalities. Both MACF1 and 16p13.11 microduplication have significant impacts on neural development, potentially leading to nerve damage or neurological diseases. This study presents a unique case of a patient simultaneously experiencing a de novo MACF1 mutation and a hereditary 16p13.11 microduplication, which has not been reported previously. CASE PRESENTATION: In this report, we describe a Chinese preterm newborn girl exhibiting the typical characteristics of 16.13.11 microduplication syndrome. These features include developmental delay, respiratory issues, feeding problems, muscle weakness, excessive joint movement, and multiple congenital abnormalities. Through whole-exome sequencing, we identified a disease-causing mutation in the MACF1 gene (c.15266T > C / p. Met5089Thr). Additionally, after microarray analysis, we confirmed the presence of a 16p13.11 microduplication (chr16:14,916,289 - 16,315,688), which was inherited from the mother. CONCLUSIONS: The patient's clinical presentation, marked by muscle weakness and multiple birth defects, may be attributed to both the de novo MACF1 mutation and the 16p13.11 duplication, which could have further amplified her severe symptoms. Genetic testing for individuals with complex clinical manifestations can offer valuable insights for diagnosis and serve as a reference for genetic counseling for both patients and their families.

Prenatal diagnosis of recurrent Kagami-Ogata syndrome inherited from a mother affected by Temple syndrome: a case report and literature review.

BACKGROUND: Kagami-Ogata syndrome (KOS) and Temple syndrome (TS) are two imprinting disorders characterized by the absence or reduced expression of maternal or paternal genes in the chromosome 14q32 region, respectively. We present a rare prenatally diagnosed case of recurrent KOS inherited from a mother affected by TS. CASE PRESENTATION: The woman's two affected pregnancies exhibited recurrent manifestations of prenatal overgrowth, polyhydramnios, and omphalocele, as well as a small bell-shaped thorax with coat-hanger ribs postnatally. Prenatal genetic testing using a single-nucleotide polymorphism array detected a 268.2-kb deletion in the chromosome 14q32 imprinted region inherited from the mother, leading to the diagnosis of KOS. Additionally, the woman carried a de novo deletion in the paternal chromosome 14q32 imprinted region and presented with short stature and small hands and feet, indicating a diagnosis of TS. CONCLUSIONS: Given the rarity of KOS as an imprinting disorder, accurate prenatal diagnosis of this rare imprinting disorder depends on two factors: (1) increasing clinician recognition of the clinical phenotype and related genetic mechanism, and (2) emphasizing the importance of imprinted regions in the CMA workflow for laboratory analysis.

Shear modulus of lower limb muscles in school-aged children with mild hypotonia.

The objective of this study is to compare shear modulus of lower limb muscles between children with hypotonia versus typical development (TD) or developmental disorders associated with altered tone. Nineteen children with mild hypotonia (mean age 9.4 ± 2.3y, 13 male) completed assessment of resting shear modulus of rectus femoris, biceps femoris (BF), tibialis anterior (TA) and gastrocnemius lateralis (GL) at short and long lengths using shear wave elastography. Data was compared with previous data from TD children and a scoping review for children with developmental disorders. Data were collated according to Net-Longitudinal Tension Angle (Net-LTA), which is the muscle length expressed as the net proximal and distal joint angles. Effects of Net-LTA (e.g., short, neutral, long) were examined according to sex, age and body mass index (BMI). In children with hypotonia, shear modulus was: higher at longer versus shorter lengths for four muscles (p < 0.01); correlated with age for BF-short (r = 0.60, p < 0.03) and GL-short (r = -0.54, p < 0.03), with BMI for BF-short (r = 0.71, p < 0.05); and not different between sexes (p > 0.05). The shear modulus values for lower limb muscles for children with mild hypotonia were lower than those for children with Duchenne Muscular Dystrophy (TA-neutral), or Cerebral Palsy (GL-neutral), but not TD children (all four muscles). In conclusion, shear modulus increases with longer muscle length (i.e. higher Net-LTA) in mildly hypotonic children. Children with mild hypotonia have lower shear modulus than children with cerebral palsy and Duchenne muscular dystrophy.

Identification of a novel nonsense SLC16A2 gene mutation in an infant with severe neurologic phenotype: A case report.

RATIONALE: Allan-Herndon-Dudley syndrome (AHDS) results from a pathogenic variant in the hemizygous subunit of the SLC16A2 gene, which encodes monocarboxylate transporter 8 and follows an X-linked recessive pattern. AHDS manifests as neuropsychomotor developmental delay, intellectual disability, movement disorders, and thyroid hormone abnormalities. It is frequently misdiagnosed as cerebral palsy or hypothyroidism. PATIENT CONCERNS: A 9-month-old male infant exhibited poor head control, hypodynamia, motor retardation, hypertonic limbs, and thyroid abnormalities. Despite levothyroxine supplementation and rehabilitation therapy, no improvements were observed. Whole-exome sequencing identified a novel nonsense mutation in SLC16A2 (c.124G > T, p.E42X), which unequivocally established the diagnosis. DIAGNOSES: AHDS was confirmed. INTERVENTIONS: Levothyroxine treatment commenced early in infancy, followed by 3 months of rehabilitation therapy, starting at 5 months of age. The combined administration of levothyroxine and methimazole was initiated at 1 year and 10 months of age, respectively. OUTCOMES: While improvements were noted in thyroid hormone levels, neurological developmental delays persisted. LESSONS: AHDS should be considered in patients presenting with atypical neurological features and thyroid hormone abnormalities such as elevated triiodothyronine and decreased thyroxine levels. The early utilization of exome sequencing aids in prompt diagnosis. The identified SLC16A2 nonsense mutation correlates with severe neurological phenotypes and adds to the spectrum of genetic variations associated with AHDS.

Neonatal X-linked myotubular myopathy with a de novo mutation: A case report and literature review. / æ–°å‘çªå˜åŸºå› çš„æ–°ç”Ÿå„¿X-è¿žé”è‚Œå°ç®¡è‚Œç— 1例并文献回顾.

X-linked myotubular myopathy (XLMTM) is a rare congenital myopathy. In February 2021, a male neonate was admitted to the West China Second University Hospital, Sichuan University, with clinical manifestations of hypotonia, accompanied by distinctive facial features, and requiring continuous ventilatory support. He was born prematurely at 36+2 weeks gestation and developed respiratory distress postnatally, followed by difficulty in weaning from mechanical ventilation. Additional clinical features included hypotonia of the limbs, swallowing dysfunction, and specific facial characteristics (elongated limbs, narrow face, high-arched palate, wrist drop, empty scrotum, elongated fingers/toes). Genetic testing confirmed the diagnosis of XLMTM. Whole-exome sequencing analysis of the family revealed no mutations in the father, paternal grandfather, or paternal grandmother, while the mother had a heterozygous mutation. The pathogenic mutation was identified as MTM1 gene (OMIM: 300415), chromosome position chrX-150649714, with a nucleotide change of c.868-2A>C. The patient exhibited typical facial features. Genetic testing is crucial for accurate diagnosis of XLMTM in infants presenting with abnormal muscle tone and distinctive facial features.

Gastro-oesophageal reflux: rare presentation of Sotos syndrome in a neonate.

Sotos syndrome is a disorder characterised by distinctive facial features, excessive growth during childhood and intellectual disability. While these criteria apply to children and adults, they fall short when applied to neonates. Hyperbilirubinaemia, large for gestational age, hypotonia and seizures, along with cardiac and renal anomalies, are known to be common presentations in neonates. Reports have also added hyperinsulinaemic hypoglycaemia as a presenting feature of Sotos syndrome in neonates. Here, we report a case of Sotos syndrome in a neonate who presented in the neonatal period with recurrent apnoeic episodes with hypotonia, which were later attributed to severe gastro-oesophageal reflux.

L-tyrosine for treatment of an infant with nemaline rod myopathy.

Nemaline rod myopathy is an extremely rare muscle disease responsible for hypotonia and poor muscle strength in infants. The disease has variable phenotypic presentations across different ages, ranging from neonatal to the adult onset and from severe to asymptomatic varieties. Clinical features, muscle biopsy and genetic testing help in diagnosis. The histopathological examination shows the presence of rod-like structures or nemaline bodies in muscles. Management remains mainly supportive, and currently, there is no available curative treatment. This case report describes an infant presenting with gross hypotonia, poor handling of secretions and multiple extubation failures who was diagnosed by clinical exome sequencing. The patient harboured compound heterozygous variants in the NEB gene suggestive of nemaline rod myopathy. The newborn showed significant improvement in muscle strength after he was started on dietary L-tyrosine supplementation. This case highlights the emerging role of L-tyrosine in the supportive care of infants with nemaline rod myopathy.

3,3',5-Triiodothyroacetic Acid Transporters.

Introduction: Thyroid hormone transporters are essential for thyroid hormones to enter target cells. Monocarboxylate transporter (MCT) 8 is a key transporter and is expressed at the blood-brain barrier (BBB), in neural cells and many other tissues. Patients with MCT8 deficiency have severe neurodevelopmental delays because of cerebral hypothyroidism and chronic sequelae of peripheral thyrotoxicosis. The T3 analog 3,3',5-triiodothyroacetic acid (TRIAC) rescued neurodevelopmental features in animal models mimicking MCT8 deficiency and improved key metabolic features in patients with MCT8 deficiency. However, the identity of the transporter(s) that facilitate TRIAC transport are unknown. Here, we screened candidate transporters that are expressed at the human BBB and/or brain-cerebrospinal fluid barrier and known thyroid hormone transporters for TRIAC transport. Materials and Methods: Plasma membrane expression was determined by cell surface biotinylation assays. Intracellular accumulation of 1 nM TRIAC was assessed in COS-1 cells expressing candidate transporters in Dulbecco's phosphate-buffered saline (DPBS)/0.1% glucose or Dulbecco's modified Eagle's medium (DMEM) with or without 0.1% bovine serum albumin (BSA). Expression of Slc22a8 was determined by fluorescent in situ hybridization in brain sections from wild-type and Mct8/Oatp1c1 knockout mice at postnatal days 12, 21, and 120. Results: In total, 59 plasma membrane transporters were selected for screening of TRIAC accumulation (n = 40 based on expression at the human BBB and/or brain-cerebrospinal fluid barrier and having small organic molecules as substrates; n = 19 known thyroid hormone transporters). Screening of the selected transporter panel showed that 18 transporters facilitated significant intracellular accumulation of TRIAC in DPBS/0.1% glucose or DMEM in the absence of BSA. In the presence of BSA, substantial transport was noted for SLCO1B1 and SLC22A8 (in DPBS/0.1% glucose and DMEM) and SLC10A1, SLC22A6, and SLC22A24 (in DMEM). The zebrafish and mouse orthologs of these transporters similarly facilitated intracellular accumulation of TRIAC. Highest Slc22a8 mRNA expression was detected in mouse brain capillary endothelial cells and choroid plexus epithelial cells at early postnatal time points, but was reduced at P120. Conclusions: Human SLC10A1, SLCO1B1, SLC22A6, SLC22A8, and SLC22A24 as well as their mouse and zebrafish orthologs are efficient TRIAC transporters. These findings contribute to the understanding of TRIAC treatment in patients with MCT8 deficiency and animal models thereof.

Multiple Congenital Anomalies-Hypotonia-Seizures Syndrome 2 Caused by a Novel PIGA Variant Not Associated with a Skewed X-Inactivation Pattern.

Germline variants in the phosphatidylinositol glycan class A (PIGA) gene, which is involved in glycosylphosphatidylinositol (GPI) biosynthesis, cause multiple congenital anomalies-hypotonia-seizures syndrome 2 (MCAHS2) with X-linked recessive inheritance. The available literature has described a pattern of almost 100% X-chromosome inactivation in mothers carrying PIGA variants. Here, we report a male infant with MCAHS2 caused by a novel PIGA variant inherited from his mother, who has a non-skewed pattern of X inactivation. Phenotypic evidence supporting the pathogenicity of the variant was obtained by flow-cytometry tests. We propose that the assessment in neutrophils of the expression of GPI-anchored proteins (GPI-APs), especially CD16, should be considered in cases with variants of unknown significance with random X-inactivation in carrier mothers in order to clarify the pathogenic role of PIGA or other gene variants linked to the synthesis of GPI-APs.

Novel 14q32.2 paternal deletion encompassing the whole DLK1 gene associated with Temple syndrome.

BACKGROUND: Temple syndrome (TS14) is a rare imprinting disorder caused by maternal UPD14, imprinting defects or paternal microdeletions which lead to an increase in the maternal expressed genes and a silencing the paternally expressed genes in the 14q32 imprinted domain. Classical TS14 phenotypic features include pre- and postnatal short stature, small hands and feet, muscular hypotonia, motor delay, feeding difficulties, weight gain, premature puberty along and precocious puberty. METHODS: An exon array comparative genomic hybridization was performed on a patient affected by psychomotor and language delay, muscular hypotonia, relative macrocephaly, and small hand and feet at two years old. At 6 years of age, the proband presented with precocious thelarche. Genes dosage and methylation within the 14q32 region were analyzed by MS-MLPA. Bisulfite PCR and pyrosequencing were employed to quantification methylation at the four known imprinted differentially methylated regions (DMR) within the 14q32 domain: DLK1 DMR, IG-DMR, MEG3 DMR and MEG8 DMR. RESULTS: The patient had inherited a 69 Kb deletion, encompassing the entire DLK1 gene, on the paternal allele. Relative hypermethylation of the two maternally methylated intervals, DLK1 and MEG8 DMRs, was observed along with normal methylation level at IG-DMR and MEG3 DMR, resulting in a phenotype consistent with TS14. Additional family members with the deletion showed modest methylation changes at both the DLK1 and MEG8 DMRs consistent with parental transmission. CONCLUSION: We describe a girl with clinical presentation suggestive of Temple syndrome resulting from a small paternal 14q32 deletion that led to DLK1 whole-gene deletion, as well as hypermethylation of the maternally methylated DLK1-DMR.

[The importance of early recognition of Prader-Willi syndrome]. / Het Prader-Willi-syndroom.

Due to its rare nature and subtle dysmorphisms, Prader-Willi syndrome can be challenging to recognize and diagnose in the neonatal period. Feeding difficulties and hypotonia ('floppy infant') are the most striking characteristics. Prader-Willi syndrome requires specific follow-up and treatment, emphasizing the importance of early recognition.We encountered an infant of three months old with severe hypotonia. The hypotonia ameliorated spontaneously over time, although feeding per nasogastric tube was necessary. There were no apparent dysmorphisms. Extensive genetic investigations showed a maternal uniparental disomy of chromosome 15, fitting with Prader-Willi syndrome explaining all symptoms. After excluding contraindications, treatment with growth hormone therapy was started. Parents were educated regarding medical emergencies specific for Prader-Willi syndrome ('medical alerts'). Although Prader-Willi syndrome is rare, it should always be considered in cases of neonatal hypotonia. Early recognition is paramount as specific recommendations and treatment are warranted.

Patient with a heterozygous pathogenic variant in CSNK2A1 gene: A new case to update the Okur-Chung neurodevelopmental syndrome.

The autosomal dominant Okur-Chung neurodevelopmental syndrome (OCNDS: OMIM #617062) is a rare neurodevelopmental disorder first described in 2016. Features include developmental delay (DD), intellectual disability (ID), behavioral problems, hypotonia, language deficits, congenital heart abnormalities, and non-specific dysmorphic facial features. OCNDS is caused by heterozygous pathogenic variants in CSNK2A1 (OMIM *115440; NM_177559.3). To date, 160 patients have been diagnosed worldwide. The number will likely increase due to the growing use of exome sequencing (ES) and genome sequencing (GS). Here, we describe a novel OCNDS patient carrying a CSNK2A1 variant (NM_177559.3:c.140G>A; NP_808227.1:p.Arg47Gln). Phenotypically, he presented with DD, ID, generalized hypotonia, speech delay, short stature, microcephaly, and dysmorphic features such as low-set ears, hypertelorism, thin upper lip, and a round face. The patient showed several signs not yet described that may extend the phenotypic spectrum of OCNDS. These include prenatal bilateral clubfeet, exotropia, and peg lateral incisors. However, unlike the majority of descriptions, he did not present sleep disturbance, seizures or gait difficulties. A literature review shows phenotypic heterogeneity for OCNDS, whether these patients have the same variant or not. This case report is an opportunity to refine the phenotype of this syndrome and raise the question of the genotype-phenotype correlation.

De novo variants in ATXN7L3 lead to developmental delay, hypotonia and distinctive facial features.

Deubiquitination is crucial for the proper functioning of numerous biological pathways, such as DNA repair, cell cycle progression, transcription, signal transduction and autophagy. Accordingly, pathogenic variants in deubiquitinating enzymes (DUBs) have been implicated in neurodevelopmental disorders and congenital abnormalities. ATXN7L3 is a component of the DUB module of the Spt-Ada-Gcn5 acetyltransferase (SAGA) complex and two other related DUB modules, and it serves as an obligate adaptor protein of three ubiquitin-specific proteases (USP22, USP27X or USP51). Through exome sequencing and by using GeneMatcher, we identified nine individuals with heterozygous variants in ATXN7L3. The core phenotype included global motor and language developmental delay, hypotonia and distinctive facial characteristics, including hypertelorism, epicanthal folds, blepharoptosis, a small nose and mouth, and low-set, posteriorly rotated ears. To assess pathogenicity, we investigated the effects of a recurrent nonsense variant [c.340C>T; p.(Arg114Ter)] in fibroblasts of an affected individual. ATXN7L3 protein levels were reduced, and deubiquitylation was impaired, as indicated by an increase in histone H2Bub1 levels. This is consistent with the previous observation of increased H2Bub1 levels in Atxn7l3-null mouse embryos, which have developmental delay and embryonic lethality. In conclusion, we present clinical information and biochemical characterization supporting ATXN7L3 variants in the pathogenesis of a rare syndromic neurodevelopmental disorder.

Non-ketotic hyperglycinaemia masquerading as a hypotonic-hyporesponsive episode following vaccination in an infant.

Non-ketotic hyperglycinaemia (NKH) is an inborn error of glycine metabolism with autosomal recessive inheritance. A female infant presented to our emergency department with intractable seizures, lethargy and hypotonia, 2 weeks after her routine vaccination. Detailed infective and metabolic workup revealed normal blood sugar, ketone, lactate ammonia, and a high level of glycine in serum and cerebrospinal fluid suggesting NKH. Diagnosis of NKH was further confirmed on genetic analysis for AMT gene mutation. The child showed clinical improvement with oral sodium benzoate. Here, we report the inheritance, pathophysiology, diagnostic approach, genetic confirmation, management and prognosis of a child with NKH.

ALG13-Congenital Disorder of Glycosylation (ALG13-CDG): Updated clinical and molecular review and clinical management guidelines.

ALG13-Congenital Disorder of Glycosylation (CDG), is a rare X-linked CDG caused by pathogenic variants in ALG13 (OMIM 300776) that affects the N-linked glycosylation pathway. Affected individuals present with a predominantly neurological manifestation during infancy. Epileptic spasms are a common presenting symptom of ALG13-CDG. Other common phenotypes include developmental delay, seizures, intellectual disability, microcephaly, and hypotonia. Current management of ALG13-CDG is targeted to address patients' symptoms. To date, less than 100 individuals have been reported with ALG13-CDG. In this article, an international group of experts in CDG reviewed all reported individuals affected with ALG13-CDG and suggested diagnostic and management guidelines for ALG13-CDG. The guidelines are based on the best available data and expert opinion. Neurological symptoms dominate the phenotype of ALG13-CDG where epileptic spasm is confirmed to be the most common presenting symptom of ALG13-CDG in association with hypotonia and developmental delay. We propose that ACTH/prednisolone treatment should be trialed first, followed by vigabatrin, however ketogenic diet has been shown to have promising results in ALG13-CDG. In order to optimize medical management, we also suggest early cardiac, gastrointestinal, skeletal, and behavioral assessments in affected patients.

Sudden unexpected postnatal collapse and BUB1B mutation: first forensic case report.

Sudden unexpected postnatal collapse (SUPC) is a sudden collapse of the clinical conditions of a full-term or near-term newborn, within the first 7 days of life, that requires resuscitation with positive ventilation and who either dies, has hypoxic-ischemic encephalopathy, or requires intensive care. The incidence of SUPC is very low, and most often presents a negative prognosis. The BUB1B gene is a mitotic checkpoint of serine/threonine kinase B that encodes a protein crucial for maintaining the correct number of chromosomes during cell division. Mutations in the BUB1B gene are linked to mosaic variegated aneuploidy syndrome 1 (MVA1), a rare autosomal recessive disorder characterized by diffuse mosaic aneuploidies involving several chromosomes and tissues. This paper discusses a case of a newborn who had a spontaneous delivery. After 2 h and 10 min, the infant showed generalized hypotonia and cyanosis, and his doctors performed orotracheal intubation, cardiac massage, pharmacological hemodynamic therapy, mechanical ventilation, antibiotic therapy, and hypothermic treatment. The newborn was discharged after 5 months with the diagnosis of hypoxic-ischemic encephalopathy. Suspecting an SUPC, a complete genetic analysis was performed demonstrating a compound heterozygous mutations in the BUB1B gene. The newborn died at 6 months of life, 1 month after discharge. A complete autopsy was performed, determining that the cause of death was due to sepsis starting from a brocopneumonic process, with outcomes of hypoxic-ischemic encephalopathy (HIE). In this scenario, it is not possible to demonstrate the causal effect of this mutation, considering that it could play a causal or concausal role in the onset of SUPC. Further research based on multicenter studies, as well as on animal models, could be very useful to clarify the pathological effect of this mutation.

Laryngeal clefts in Prader-Willi syndrome: Feeding difficulties and aspiration not always caused by hypotonia.

Feeding difficulties, aspiration, and failure to thrive in infancy are commonly seen in patients with Prader-Willi Syndrome (PWS) and attributed to hypotonia. Patients with PWS and laryngeal clefts were identified by review of medical records at three tertiary care children's hospitals between 2017 and 2022. We present three patients with PWS with feeding difficulties who were also found to have laryngeal clefts which likely contributed to their feeding difficulties. Additional factors such as airway anomalies should be considered in patients with PWS, especially when swallowing dysfunction, dysphagia, or abnormal swallow evaluations are present.

Identification of Iodotyrosines as Novel Substrates for the Thyroid Hormone Transporter MCT8.

Background: Monocarboxylate transporter 8 (MCT8) is the most specific thyroid hormone transporter identified to date, deficiency of which has been associated with severe intellectual and motor disability and abnormal serum thyroid function tests. However, it is presently unknown if MCT8, similar to other thyroid hormone transporters, also accepts additional substrates, and if disruption of their transport may contribute to the observed phenotype. Methods: In this study, we aimed to identify such substrates by applying liquid chromatography-mass spectrometry-based metabolome analysis in lysates of control and MCT8-overexpressing Xenopus oocytes. A subset of identified candidate substrates were validated by direct transport studies in transiently transfected COS-1 cells and human fibroblasts, which endogenously express MCT8. Moreover, transport characteristics were determined, including transport saturation and cis-inhibition potency of thyroid hormone transport. Results: Metabolome analysis identified 21 m/z ratios, corresponding to 87 candidate metabolites, with a 2.0-times differential abundance in MCT8-injected oocytes compared with controls. These metabolites included 3,5-diiodotyrosine (DIT) and several amino acids, including glutamate and glutamine. In accordance, MCT8-expressing COS-1 cells had 2.2-times lower intracellular accumulation of [125I]-DIT compared with control cells. This effect was largely blocked in the presence of 3,3',5-triiodothyronine (T3) (IC50: 2.5 ± 1.5 µM) or thyroxine (T4) (IC50: 5.8 ± 1.3 µM). Conversely, increasing concentrations of DIT enhanced the accumulation of T3 and T4. The MCT8-specific inhibitor silychristin increased the intracellular accumulation of DIT in human fibroblasts. COS-1 cells expressing MCT8 also exhibited a 50% reduction in intracellular accumulation of [125I]-3-monoiodotyrosine (MIT). In contrast, COS-1 cells expressing MCT8 did not alter the intracellular accumulation of [3H]-glutamate or [3H]-glutamine. However, studies in human fibroblasts showed a 1.5-1.9 times higher glutamate uptake in control fibroblasts compared with fibroblasts derived from patients with MCT8 deficiency, which was not affected in the presence of silychristin. Conclusions: Taken together, our results suggest that the iodotyrosines DIT and MIT can be exported by MCT8. MIT and DIT interfere with MCT8-mediated transport of thyroid hormone in vitro and vice versa. Future studies should elucidate if MCT8, being highly expressed in thyroidal follicular cells, also transports iodotyrosines in vivo.

Biallelic loss-of-function variants of ZFTRAF1 cause neurodevelopmental disorder with microcephaly and hypotonia.

PURPOSE: Neurodevelopmental disorders exhibit clinical and genetic heterogeneity, ergo manifest dysfunction in components of diverse cellular pathways; the precise pathomechanism for the majority remains elusive. METHODS: We studied 5 affected individuals from 3 unrelated families manifesting global developmental delay, postnatal microcephaly, and hypotonia. We used exome sequencing and prioritized variants that were subsequently characterized using immunofluorescence, immunoblotting, pulldown assays, and RNA sequencing. RESULTS: We identified biallelic variants in ZFTRAF1, encoding a protein of yet unknown function. Four affected individuals from 2 unrelated families segregated 2 homozygous frameshift variants in ZFTRAF1, whereas, in the third family, an intronic splice site variant was detected. We investigated ZFTRAF1 at the cellular level and signified it as a nucleocytoplasmic protein in different human cell lines. ZFTRAF1 was completely absent in the fibroblasts of 2 affected individuals. We also identified 110 interacting proteins enriched in mRNA processing and autophagy-related pathways. Based on profiling of autophagy markers, patient-derived fibroblasts show irregularities in the protein degradation process. CONCLUSION: Thus, our findings suggest that biallelic variants of ZFTRAF1 cause a severe neurodevelopmental disorder.