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Purpose Pathogenic variants in ARID1B are one of the most frequent causes of intellectual disability (ID) as determined by large-scale exome sequencing studies. Most studies published thus far describe clinically diagnosed Coffin–Siris patients (ARID1B-CSS) and it is unclear whether these data are representative for patients identified through sequencing of unbiased ID cohorts (ARID1B-ID). We therefore sought to determine genotypic and phenotypic differences between ARID1B-ID and ARID1B-CSS. In parallel, we investigated the effect of different methods of phenotype reporting. Methods Clinicians entered clinical data in an extensive web-based survey. Results 79 ARID1B-CSS and 64 ARID1B-ID patients were included. CSS-associated dysmorphic features, such as thick eyebrows, long eyelashes, thick alae nasi, long and/or broad philtrum, small nails and small or absent fifth distal phalanx and hypertrichosis, were observed significantly more often ( p  < 0.001) in ARID1B-CSS patients. No other significant differences were identified. Conclusion There are only minor differences between ARID1B-ID and ARID1B-CSS patients. ARID1B-related disorders seem to consist of a spectrum, and patients should be managed similarly. We demonstrated that data collection methods without an explicit option to report the absence of a feature (such as most Human Phenotype Ontology-based methods) tended to underestimate gene-related features.

Multiple sulfatase deficiency (MSD) is a lysosomal storage disease caused by a deficiency of formylglycine‐generating enzyme due to SUMF1 defects. MSD may be misdiagnosed as metachromatic leukodystrophy (MLD), as neurological and neuroimaging findings are similar, and arylsulfatase A (ARSA) deficiency and enhanced urinary sulfatide excretion may also occur. While ARSA deficiency seems a cause for neurological symptoms and later neurodegenerative disease course, deficiency of other sulfatases results in clinical features such as dysmorphism, dysostosis, or ichthyosis. We report on a girl and a boy of the same origin presenting with severe ARSA deficiency and neurological and neuroimaging features compatible with MLD. However, exome sequencing revealed not yet described homozygosity of the missense variant c.529G > C, p.Ala177Pro in SUMF1. We asked whether dynamics of disease course differs between MSD and MLD. Comparison to a cohort of 59 MLD patients revealed different disease course concerning onset and disease progression in both MSD patients. The MSD patients showed first gross motor symptoms earlier than most patients with juvenile MLD (<10th percentile of Gross‐Motor‐Function in MLD [GMFC‐MLD] 1). However, subsequent motor decline was more protracted (75th and 90th percentile of GMFC‐MLD 2 (loss of independent walking) and 75th percentile of GMFC‐MLD 5 (loss of any locomotion)). Language decline started clearly after 50th percentile of juvenile MLD and progressed rapidly. Thus, dynamics of disease course may be a further clue for the characterization of MSD. These data may contribute to knowledge of natural course of ultra‐rare MSD and be relevant for counseling and therapy.

Background Krabbe disease or globoid cell leukodystrophy is a severe neurodegenerative disorder caused by a defect in the GALC gene leading to a deficiency of the enzyme ß-galactocerebrosidase. The aim of this work was to describe the natural disease course covering the whole spectrum of the disease. Methods Natural history data were collected with a standardized questionnaire, supplemented by medical record data. We defined different forms of the disease according to Abdelhalim et al. (2014). Developmental and disease trajectories were described based on the acquisition and loss of milestones as well as the time of first clearly identifiable symptoms and needs such as spasticity, seizures and tube feeding. MRI was assessed using the scoring system by Loes et al. (1999) and in addition a pattern recognition approach, based on Abdelhalim et al. (2014). Results Thirty-eight patients were identified, from 27 of these patients 40 MRIs were available; 30 (79%) had an infantile onset, showing first symptoms in their first year of life, almost all (27 out of 30) starting in the first six months. A later onset after the first year of life was observed in 8 patients (21%, range 18 months to 60 years). Irritability, abnormalities in movement pattern as well as general developmental regression were the first symptoms in the infantile group; disease course was severe with rapid progression, e.g. loss of visual fixation, need for tube feeding and then an early death. Gait disorders were the first symptoms in all patients of the later onset groups; progression was variable. The different forms of the disease were characterized by different MRI patterns (infantile: diffuse white matter involvement and cerebellar structures specifically affected, later onset: parieto-occipital white matter and splenium affected, adult: motor tracts specifically affected). Conclusion This is the first description of the natural history of Krabbe disease in a larger European cohort using developmental, clinical and MRI data. We would like to highlight the very different clinical and MRI characteristics of the later onset forms. These data are important for counselling affected patients and families and may serve as a basis for future treatment trials.

Background Metachromatic Leukodystrophy (MLD) is a rare autosomal-recessive lysosomal storage disorder caused by mutations in the ARSA gene. While interventional trials often use untreated siblings as controls, the genotype-phenotype correlation is only partly understood, and the variability of the clinical course between siblings is unclear with some evidence for a discrepant clinical course in juvenile patients. The aim of this study was to systematically investigate the phenotypic variation in MLD siblings in comparison to the variability in a larger MLD cohort and to case reports published in literature. Results Detailed clinical information was available from 12 sibling-pairs (3 late-infantile, 9 juvenile) and 61 single patients (29 late-infantile, 32 juvenile). Variability of age at onset was similar between the siblings and randomly chosen pairs of the remaining cohort (no statistically different Euclidean distances). However, in children with juvenile MLD both the type of first symptoms and the dynamic of the disease were less variable between siblings compared to the general cohort. In late-infantile patients, type of first symptoms and dynamic of disease were similarly homogeneous between siblings and the whole MLD cohort. Thirteen published case reports of families with affected siblings with MLD are presented with similar findings. Conclusions In a systematic analysis of phenotypic variation in families with MLD, siblings with the late-infantile form showed a similar variability as unrelated pairs of children with late-infantile MLD, whereas siblings with juvenile MLD showed a more homogeneous phenotype regarding type of first symptoms and disease evolution in comparison to unrelated children with juvenile MLD, but not regarding their age at onset. These results are highly relevant with respect to the evaluation of treatment effects and for counseling of families with affected siblings.

Homozygous mutation of TBC1 domain-containing kinase ( TBCK ) is the cause of a very recently defined severe childhood disorder, which is characterized by severe hypotonia, global developmental delay, intellectual disability, epilepsy, characteristic facies and premature death. The link between TBCK loss of function and symptoms in patients with TBCK deficiency disorder (TBCK-DD) remains elusive. Here we demonstrate for the first time the histopathological characteristics of TBCK deficiency consisting of 1) a widespread and massive accumulation of lipofuscin storage material in neurons of the central nervous system without notable neuronal degeneration, 2) storage deposits in few astrocytes, 3) carbohydrate-rich deposits in brain, spleen and liver and 4) vacuolated lymphocytes. Biochemical examinations ruled out more than 20 known lysosomal storage diseases. These investigations strikingly uncover TBCK-DD as a novel type of lysosomal storage disease which is characterized by different storage products rather than one specific type of accumulated material. Due to the clear predominance of intraneuronal lipofuscin storage material and the characteristic clinical presentation we propose to classify this disease as a new subtype of neuronal ceroid lipofuscinosis (CLN15). Our results and previous reports suggest an autophagosomal-lysosomal dysfunction caused by enhanced mTORC1-mediated autophagosome formation and reduced Rab-mediated autophagosome-lysosome fusion, thus disclosing potential novel targets for therapeutic approaches in TBCK-DD.

Background MAGEL2 -associated Schaaf-Yang syndrome (SHFYNG, OMIM #615547, ORPHA: 398069), which was identified in 2013, is a rare disorder caused by truncating variants of the paternal copy of MAGEL2 , which is localized in the imprinted region on 15q11.2q13. The phenotype of SHFYNG in childhood partially overlaps with that of the well-established Prader–Willi syndrome (PWS, OMIM #176270). While larger numbers of younger individuals with SHFYNG have been recently published, the phenotype in adulthood is not well established. We recruited 7 adult individuals (aged 18 to 36) with molecularly confirmed SHFYNG and collected data regarding the clinical profile including eating habits, sleep, behavior, personal autonomy, psychiatric abnormalities and other medical conditions, as well as information about the respective phenotypes in childhood. Results Within our small cohort, we identified a range of common features, such as disturbed sleep, hypoactivity, social withdrawal and anxiety, but also noted considerable differences at the level of personal autonomy and skills. Behavioral problems were frequent, and a majority of individuals displayed weight gain and food-seeking behavior, along with mild intellectual disability or borderline intellectual function. Classical symptoms of SHFYNG in childhood were reported for most individuals. Conclusion Our findings indicate a high variability of the functional abilities and social participation of adults with SHFYNG. A high prevalence of obesity within our cohort was notable, and uncontrollable food intake was a major concern for some caregivers. The phenotypes of PWS and SHFYNG in adulthood might be more difficult to discern than the phenotypes in childhood. Molecular genetic testing for SHFYNG should therefore be considered in adults with the suspected diagnosis of PWS, if testing for PWS has been negative.

The original version of this Article contained an error in the spelling of the author Pleuntje J. van der Sluijs, which was incorrectly given as Eline (P. J.) van der Sluijs. This has now been corrected in both the PDF and HTML versions of the Article.

Introduction: Glycogen storage disease type VI (GSD VI) is a disorder of glycogen metabolism due to mutations in the PYGL gene. Patients with GSD VI usually present with hepatomegaly, recurrent hypoglycemia, and short stature. Results: We report on two non-related Turkish patients with a novel homozygous splice site variant, c.345G>A, which was shown to lead to exon 2 skipping of the PYGL-mRNA by exome and transcriptome analysis. According to an in silico analysis, deletion Arg82_Gln115del is predicted to impair protein stability and possibly AMP binding. Conclusion: GSD VI is a possibly underdiagnosed disorder, and in the era of next generation sequencing, more and more patients with variants of unknown significance in the PYGL-gene will be identified. Techniques, such as transcriptome analysis, are important tools to confirm the pathogenicity and to determine therapeutic measures based on genetic results.

BackgroundDisruptions of the FOXP2 gene, encoding a forkhead transcription factor, are the first known monogenic cause of a speech and language disorder. So far, mainly chromosomal rearrangements such as translocations or larger deletions affecting FOXP2 have been reported. Intragenic deletions or convincingly pathogenic point mutations in FOXP2 have up to date only been reported in three families. We thus aimed at a further characterisation of the mutational and clinical spectrum.MethodsChromosomal microarray testing, trio exome sequencing, multigene panel sequencing and targeted sequencing of FOXP2 were performed in individuals with variable developmental disorders, and speech and language deficits.ResultsWe identified four different truncating mutations, two novel missense mutations within the forkhead domain and an intragenic deletion in FOXP2 in 14 individuals from eight unrelated families. Mutations occurred de novo in four families and were inherited from an affected parent in the other four. All index patients presented with various manifestations of language and speech impairment. Apart from two individuals with normal onset of speech, age of first words was between 4 and 7 years. Articulation difficulties such as slurred speech, dyspraxia, stuttering and poor pronunciation were frequently noted. Motor development was normal or only mildly delayed. Mild cognitive impairment was reported for most individuals.ConclusionsBy identifying intragenic deletions or mutations in 14 individuals from eight unrelated families with variable developmental delay/cognitive impairment and speech and language deficits, we considerably broaden the mutational and clinical spectrum associated with aberrations in FOXP2.

Individuals with ultrarare disorders pose a structural challenge for healthcare systems since expert clinical knowledge is required to establish diagnoses. In TRANSLATE NAMSE, a 3-year prospective study, we evaluated a novel diagnostic concept based on multidisciplinary expertise in Germany. Here we present the systematic investigation of the phenotypic and molecular genetic data of 1,577 patients who had undergone exome sequencing and were partially analyzed with next-generation phenotyping approaches. Molecular genetic diagnoses were established in 32% of the patients totaling 370 distinct molecular genetic causes, most with prevalence below 1:50,000. During the diagnostic process, 34 novel and 23 candidate genotype–phenotype associations were identified, mainly in individuals with neurodevelopmental disorders. Sequencing data of the subcohort that consented to computer-assisted analysis of their facial images with GestaltMatcher could be prioritized more efficiently compared with approaches based solely on clinical features and molecular scores. Our study demonstrates the synergy of using next-generation sequencing and phenotyping for diagnosing ultrarare diseases in routine healthcare and discovering novel etiologies by multidisciplinary teams. Exome sequencing within a structured diagnostic process for rare diseases in Germany shows how facial image analysis and machine learning can guide variant prioritization and uncover many ultrarare diseases.