Population-level deficit of homozygosity unveils CPSF3 as an intellectual disability syndrome gene.

Predicting the pathogenicity of biallelic missense variants can be challenging. Here, we use a deficit of observed homozygous carriers of missense variants, versus an expected number in a set of 153,054 chip-genotyped Icelanders, to identify potentially pathogenic genotypes. We follow three missense variants with a complete deficit of homozygosity and find that their pathogenic effect in homozygous state ranges from severe childhood disease to early embryonic lethality. One of these variants is in CPSF3, a gene not previously linked to disease. From a set of clinically sequenced Icelanders, and by sequencing archival samples targeted through the Icelandic genealogy, we find four homozygous carriers. Additionally, we find two homozygous carriers of Mexican descent of another missense variant in CPSF3. All six homozygous carriers of missense variants in CPSF3 show severe intellectual disability, seizures, microcephaly, and abnormal muscle tone. Here, we show how the absence of certain homozygous genotypes from a large population set can elucidate causes of previously unexplained recessive diseases and early miscarriage.

NANS-CDG: Delineation of the Genetic, Biochemical, and Clinical Spectrum.

Background: NANS-CDG is a recently described congenital disorder of glycosylation caused by biallelic genetic variants in NANS, encoding an essential enzyme in de novo sialic acid synthesis. Sialic acid at the end of glycoconjugates plays a key role in biological processes such as brain and skeletal development. Here, we present an observational cohort study to delineate the genetic, biochemical, and clinical phenotype and assess possible correlations. Methods: Medical and laboratory records were reviewed with retrospective extraction and analysis of genetic, biochemical, and clinical data (2016-2020). Results: Nine NANS-CDG patients (nine families, six countries) referred to the Radboudumc CDG Center of Expertise were included. Phenotyping confirmed the hallmark features including intellectual developmental disorder (IDD) (n = 9/9; 100%), facial dysmorphisms (n = 9/9; 100%), neurologic impairment (n = 9/9; 100%), short stature (n = 8/9; 89%), skeletal dysplasia (n = 8/9; 89%), and short limbs (n = 8/9; 89%). Newly identified features include ophthalmological abnormalities (n = 6/9; 67%), an abnormal septum pellucidum (n = 6/9; 67%), (progressive) cerebral atrophy and ventricular dilatation (n = 5/9; 56%), gastrointestinal dysfunction (n = 5/9; 56%), thrombocytopenia (n = 5/9; 56%), and hypo-low-density lipoprotein cholesterol (n = 4/9; 44%). Biochemically, elevated urinary excretion of N-acetylmannosamine (ManNAc) is pathognomonic, the concentrations of which show a significant correlation with clinical severity. Genotypically, eight novel NANS variants were identified. Three severely affected patients harbored identical compound heterozygous pathogenic variants, one of whom was initiated on experimental prenatal and postnatal treatment with oral sialic acid. This patient showed markedly better psychomotor development than the other two genotypically identical males. Conclusions: ManNAc screening should be considered in all patients with IDD, short stature with short limbs, facial dysmorphisms, neurologic impairment, and an abnormal septum pellucidum +/- congenital and neurodegenerative lesions on brain imaging, to establish a precise diagnosis and contribute to prognostication. Personalized management includes accurate genetic counseling and access to proper supports and tailored care for gastrointestinal symptoms, thrombocytopenia, and epilepsy, as well as rehabilitation services for cognitive and physical impairments. Motivated by the short-term positive effects of experimental treatment with oral sialic, we have initiated this intervention with protocolized follow-up of neurologic, systemic, and growth outcomes in four patients. Research is ongoing to unravel pathophysiology and identify novel therapeutic targets.

Longterm Outcomes of Temporomandibular Joints in Juvenile Idiopathic Arthritis: 17 Years of Followup of a Nordic Juvenile Idiopathic Arthritis Cohort.

OBJECTIVE: To determine the prevalence of orofacial symptoms, dysfunctions, and deformities of the temporomandibular joint (TMJ) in juvenile idiopathic arthritis (JIA) 17 years after disease onset. METHODS: Drawn from a prospective, population-based Nordic JIA cohort with disease onset from 1997 to 2000, 420 consecutive cases were eligible for orofacial evaluation of TMJ involvement. The followup visit included demographic data, a standardized clinical orofacial examination, and full-face cone-beam computed tomography (CBCT). For comparison, 200 age-matched healthy controls were used. RESULTS: Of 420 eligible participants with JIA, 265 (63%) were included (mean age 23.5 ± 4.2 yrs) and completed a standardized clinical orofacial examination. Of these, 245 had a full-face CBCT performed. At least 1 orofacial symptom was reported by 33%. Compared to controls, the JIA group significantly more often reported TMJ pain, TMJ morning stiffness, and limitation on chewing. Further, among participants reporting complaints, the number of symptoms was also higher in JIA. The mean maximal incisal opening was lower in the JIA group (p < 0.001), and TMJ pain on palpation was more frequent. Condylar deformities and/or erosions were observed in 61% as assessed by CBCT, showing bilateral changes in about 70%. Risk factors of condylar deformities were orofacial dysfunction or biologic treatment; enthesitis-related arthritis was protective. CONCLUSION: This study of the longterm consequences of TMJ involvement in a population-based JIA cohort reports persistence of comprehensive symptoms, dysfunctions, and damage of the TMJ into adulthood. We suggest interdisciplinary followup of JIA patients also in adulthood.

Trends in prevalence and characteristics of cerebral palsy among Icelandic children born 1990 to 2003.

AIM: To describe trends in cerebral palsy (CP) prevalence, severity, and associated impairments among 139 Icelandic children (65 males, 74 females) born from 1990 to 1996 (period one) and 1997 to 2003 (period two). METHOD: A population-based study using systematically collected data on motor functioning and associated impairments of children with CP. Mean age at assessment was 5 years 5 months (SD 7.68 mo) in period one and 5 years 5 months (SD 10.44 mo) in period two. Infants with postneonatal CP were excluded. RESULTS: Prevalence of CP per 1000 live births was 2.2 in period one and 2.3 in period two (p=0.862); it decreased from 1.5 to 0.9 for children born at term, was stable for preterm births, but increased from 33.7 to 114.6 for very preterm births (p=0.002). Concurrently, neonatal and infant mortality rates decreased in Iceland. The proportion of children born preterm increased over time (p=0.002), whereas improvements in gross motor function assessed with the Gross Motor Function Classification System were confined to term births (p=0.009). The proportion of children with diplegia increased, accompanied by a decrease in the proportion with quadriplegia (p=0.047). Furthermore, among term births there was a significant reduction over time in the proportion of children with epilepsy (p=0.030) and in the proportion with two or more associated impairments (p=0.030). INTERPRETATION: Although CP prevalence remained stable over 14 years, we observed a decrease in prevalence and severity of the disability among term births.

Nationwide Incidence of Acquired Central Nervous System Demyelination in Icelandic Children.

INTRODUCTION: Recognizing acquired demyelinating syndromes and multiple sclerosis is important to commence early treatment. The objective of this study was to describe the incidence of acquired demyelinating syndromes and multiple sclerosis among the entire Icelandic pediatric population according to recently promoted criteria. PATIENTS AND METHODS: The study included all children in Iceland (<18 years) with acquired demyelinating syndromes and multiple sclerosis from 1990 to 2009 with a minimum of 5-year follow-up. Clinical data were gathered and radiological images reviewed. The cohort included all patients with acquired demyelinating syndromes and multiple sclerosis in the Icelandic pediatric population. RESULTS: Eighteen patients with acquired demyelinating syndromes and multiple sclerosis were included, the total annual incidence being 1.15/100,000 (acquired demyelinating syndromes 1.02 and multiple sclerosis 0.45/100,000). The median age at diagnosis was 14.25 years (range 1.25-17.5 years). Thirteen patients were initially diagnosed with clinically isolated syndrome, two had acute disseminated encephalomyelitis, two had multiple sclerosis, and one had neuromyelitis optica. Seven children were diagnosed with multiple sclerosis; three patients with clinically isolated syndrome developed multiple sclerosis after the age of 18 and were not included in the multiple sclerosis group. The gender ratio was equal. Of the nine girls, seven were diagnosed with clinically isolated syndrome. Most patients (11 of 18) were diagnosed during the period January through March. Oligoclonal bands in cerebrospinal fluid were exclusively found in patients with multiple sclerosis and clinically isolated syndrome and 13 of 14 available magnetic resonance images revealed clear abnormalities. CONCLUSION: The annual incidence of acquired demyelinating syndromes and multiple sclerosis in Iceland was 1.15/100,000 children. The risk of progression from clinically isolated syndrome to multiple sclerosis was high. There was no female preponderance.

Large-scale whole-genome sequencing of the Icelandic population.

Here we describe the insights gained from sequencing the whole genomes of 2,636 Icelanders to a median depth of 20×. We found 20 million SNPs and 1.5 million insertions-deletions (indels). We describe the density and frequency spectra of sequence variants in relation to their functional annotation, gene position, pathway and conservation score. We demonstrate an excess of homozygosity and rare protein-coding variants in Iceland. We imputed these variants into 104,220 individuals down to a minor allele frequency of 0.1% and found a recessive frameshift mutation in MYL4 that causes early-onset atrial fibrillation, several mutations in ABCB4 that increase risk of liver diseases and an intronic variant in GNAS associating with increased thyroid-stimulating hormone levels when maternally inherited. These data provide a study design that can be used to determine how variation in the sequence of the human genome gives rise to human diversity.

Anticoagulation therapy in cerebral sinovenous thrombosis and ulcerative colitis in children.

We describe four pediatric patients with ulcerative colitis and cerebral sinovenous thrombosis and review the pediatric and adult literature on the treatment of sinovenous thrombosis. All of our patients had headache as the initial complaint with onset during an ulcerative colitis flare. Evaluation for hypercoagulable states revealed heterozygosity for prothrombin gene mutation and increased homocysteine level in one patient and mild elevation of anticardiolipin antibodies in two patients. Treatment in the acute period included thrombolysis, heparin, and low-molecular-weight heparin. Chronic therapy included warfarin, low-molecular-weight heparin, and aspirin. Peripheral vein thrombosis occurred in two patients while not on antiplatelet or anticoagulation therapy. Neurologic outcome was positive in this series without complications of therapy, suggesting that aggressive therapy should be considered. Although anticoagulation therapy of sinovenous thrombosis is controversial, particularly in the context of intestinal hemorrhage, it can be beneficial given the possibility of an ongoing hypercoagulable state.