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Hereditary spastic paraplegia (HSP) is a group of disorders with predominant symptoms of lower-extremity weakness and spasticity. Despite the delineation of numerous genetic causes of HSP, a significant portion of individuals with HSP remain molecularly undiagnosed. Through exome sequencing, we identified five unrelated families with childhood-onset nonsyndromic HSP, all presenting with progressive spastic gait, leg clonus, and toe walking starting from 7 to 8 years old. A recurrent two-base pair deletion (c.426_427delGA, p.K143Sfs*15) in the UBAP1 gene was found in four families, and a similar variant (c.475_476delTT, p.F159*) was detected in a fifth family. The variant was confirmed to be de novo in two families and inherited from an affected parent in two other families. RNA studies performed in lymphocytes from one patient with the de novo c.426_427delGA variant demonstrated escape of nonsense-mediated decay of the UBAP1 mutant transcript, suggesting the generation of a truncated protein. Both variants identified in this study are predicted to result in truncated proteins losing the capacity of binding to ubiquitinated proteins, hence appearing to exhibit a dominant-negative effect on the normal function of the endosome-specific endosomal sorting complexes required for the transport-I complex., (© 2019 Wiley Periodicals, Inc.)

Purpose: Sixty to seventy-five percent of individuals with rare and undiagnosed phenotypes remain undiagnosed after exome sequencing (ES). With standard ES reanalysis resolving 10-15% of the ES negatives, further approaches are necessary to maximize diagnoses in these individuals., Methods: In 38 ES negative patients an individualized genomic-phenotypic approach was employed utilizing (1) phenotyping; (2) reanalyses of FASTQ files, with innovative bioinformatics; (3) targeted molecular testing; (4) genome sequencing (GS); and (5) conferring of clinical diagnoses when pathognomonic clinical findings occurred., Results: Certain and highly likely diagnoses were made in 18/38 (47%) individuals, including identifying two new developmental disorders. The majority of diagnoses (>70%) were due to our bioinformatics, phenotyping, and targeted testing identifying variants that were undetected or not prioritized on prior ES. GS diagnosed 3/18 individuals with structural variants not amenable to ES. Additionally, tentative diagnoses were made in 3 (8%), and in 5 individuals (13%) candidate genes were identified. Overall, diagnoses/potential leads were identified in 26/38 (68%)., Conclusions: Our comprehensive approach to ES negatives maximizes the ES and clinical data for both diagnoses and candidate gene identification, without GS in the majority. This iterative approach is cost-effective and is pertinent to the current conundrum of ES negatives.

Background: Neural tube defects (NTD) have a strong genetic component, with up to 70% of variance in human prevalence determined by heritable factors. Although the identification of causal DNA variants by sequencing candidate genes from functionally relevant pathways and model organisms has provided some success, alternative approaches are demanded., Methods: Next generation sequencing platforms are facilitating the production of massive amounts of sequencing data, primarily from the protein coding regions of the genome, at a faster rate and cheaper cost than has previously been possible. These platforms are permitting the identification of variants (de novo, rare, and common) that are drivers of NYTD etiology, and the cost of the approach allows for the screening of increased numbers of affected and unaffected individuals from NTD families and in simplex cases., Conclusion: The next generation sequencing platforms represent a powerful tool in the armory of the genetics researcher to identify the causal genetic basis of NTDs., (© 2014 Wiley Periodicals, Inc.)

Chiari Type I Malformation (CMI) is characterized by displacement of the cerebellar tonsils below the base of the skull, resulting in significant neurologic morbidity. Although multiple lines of evidence support a genetic contribution to disease, no genes have been identified. We therefore conducted the largest whole genome linkage screen to date using 367 individuals from 66 families with at least two individuals presenting with nonsyndromic CMI with or without syringomyelia. Initial findings across all 66 families showed minimal evidence for linkage due to suspected genetic heterogeneity. In order to improve power to localize susceptibility genes, stratified linkage analyses were performed using clinical criteria to differentiate families based on etiologic factors. Families were stratified on the presence or absence of clinical features associated with connective tissue disorders (CTDs) since CMI and CTDs frequently co-occur and it has been proposed that CMI patients with CTDs represent a distinct class of patients with a different underlying disease mechanism. Stratified linkage analyses resulted in a marked increase in evidence of linkage to multiple genomic regions consistent with reduced genetic heterogeneity. Of particular interest were two regions (Chr8, Max LOD = 3.04; Chr12, Max LOD = 2.09) identified within the subset of "CTD-negative" families, both of which harbor growth differentiation factors (GDF6, GDF3) implicated in the development of Klippel-Feil syndrome (KFS). Interestingly, roughly 3-5% of CMI patients are diagnosed with KFS. In order to investigate the possibility that CMI and KFS are allelic, GDF3 and GDF6 were sequenced leading to the identification of a previously known KFS missense mutation and potential regulatory variants in GDF6. This study has demonstrated the value of reducing genetic heterogeneity by clinical stratification implicating several convincing biological candidates and further supporting the hypothesis that multiple, distinct mechanisms are responsible for CMI.