Mutations in TBCK, Encoding TBC1-Domain-Containing Kinase, Lead to a Recognizable Syndrome of Intellectual Disability and Hypotonia.

Through an international multi-center collaboration, 13 individuals from nine unrelated families and affected by likely pathogenic biallelic variants in TBC1-domain-containing kinase (TBCK) were identified through whole-exome sequencing. All affected individuals were found to share a core phenotype of intellectual disability and hypotonia, and many had seizures and showed brain atrophy and white-matter changes on neuroimaging. Minor non-specific facial dysmorphism was also noted in some individuals, including multiple older children who developed coarse features similar to those of storage disorders. TBCK has been shown to regulate the mammalian target of rapamycin (mTOR) signaling pathway, which is also stimulated by exogenous leucine supplementation. TBCK was absent in cells from affected individuals, and decreased phosphorylation of phospho-ribosomal protein S6 was also observed, a finding suggestive of downregulation of mTOR signaling. Lastly, we demonstrated that activation of the mTOR pathway in response to L-leucine supplementation was retained, suggesting a possible avenue for directed therapies for this condition.

Variants of uncertain significance in newborn screening disorders: implications for large-scale genomic sequencing.

PURPOSE: As exome and genome sequencing using high-throughput sequencing technologies move rapidly into the diagnostic process, laboratories and clinicians need to develop a strategy for dealing with uncertain findings. A commitment must be made to minimize these findings, and all parties may need to make adjustments to their processes. The information required to reclassify these variants is often available but not communicated to all relevant parties. METHODS: To illustrate these issues, we focused on three well-characterized monogenic, metabolic disorders included in newborn screens: classic galactosemia, caused by GALT variants; phenylketonuria, caused by PAH variants; and medium-chain acyl-CoA dehydrogenase (MCAD) deficiency, caused by ACADM variants. In 10 years of clinical molecular testing, we have observed 134 unique GALT variants, 46 of which were variants of uncertain significance (VUS). In PAH, we observed 132 variants, including 17 VUS, and for ACADM, we observed 64 unique variants, of which 33 were uncertain. CONCLUSION: After this review, 17 VUS (37%; 7 in ACADM, 9 in GALT, and 1 in PAH) were reclassified from uncertain (6 to benign or likely benign and 11 to pathogenic or likely pathogenic). We identified common types of missing information that would have helped make a definitive classification and categorized this information by ease and cost to obtain.Genet Med 19 1, 77-82.

A 7-month-old male with Allan-Herndon-Dudley syndrome and the power of T3.

Allan-Herndon-Dudley syndrome (AHDS, MIM 300523) is an X-linked neurodegenerative disorder characterized by intellectual disability, severe hypotonia, diminished muscle mass, and progressive spastic paraplegia. All affected males have pathognomonic thyroid profiles with an elevated T3 , low-normal free T4 , and normal TSH. Mutations in the monocarboxylate transporter 8 (MCT8) gene, SLC16A2, have been found to be causative. Here, we describe a proband whose extensive evaluation and ultimate diagnosis of AHDS unmasked three previously undiagnosed generations of affected individuals in one family. This case illustrates the need for clinicians to consider obtaining full thyroid studies on individuals with the non-specific findings of severe hypotonia, failure to thrive, and gross motor delay.