Novel TCAP mutation c.32C>A causing limb girdle muscular dystrophy 2G

TCAP encoded telethonin is a 19 kDa protein, which plays an important role in anchoring titin in Z disc of the sarcomere and is known to cause LGMD2G, a rare muscle disorder characterised by proximal and distal lower limb weakness, calf hypertrophy and loss of ambulation. A total of 300 individuals with ARLGMD were recruited for this study. Among these we identified 8 clinically well characterised LGMD2G cases from 7 unrelated Dravidian families. Clinical examination revealed predominantly proximo - distal form of weakness, scapular winging, muscle atrophy, calf hypertrophy and foot drop, immunoblot showed either complete absence or severe reduction of telethonin. Genetic analysis revealed a novel nonsense homozygous mutation c.32C>A, p.(Ser11*) in three patients of a consanguineous family and an 8 bp homozygous duplication c.26_33dupAGGTGTCG, p.(Arg12fs31*) in another patient. Both mutations possibly lead to truncated protein or nonsense mediated decay. We could not find any functionally significant TCAP mutation in the remaining 6 samples, except for two other polymorphisms, c.453A>C, p.( = ) and c.-178G>T, which were found in cases and controls. This is the first report from India to demonstrate TCAP association with LGMD2G

Congenital myasthenic syndrome with mild intellectual disability caused by a recurrent SLC25A1 variant

Abstract: Congenital myasthenic syndromes (CMS) are a clinically and genetically heterogeneous group of disorders caused by mutations which lead to impaired neuromuscular transmission. SLC25A1 encodes a mitochondrial citrate carrier, associated mainly with the severe neurometabolic disease combined D-2- and L-2-hydroxyglutaric aciduria (D/L-2-HGA). We previously reported a single family with a homozygous missense variant in SLC25A1 with a phenotype restricted to relatively mild CMS with intellectual disability, but to date no additional cases of this CMS subtype had been reported. Here, we performed whole exome sequencing (WES) in three additional and unrelated families presenting with CMS and mild intellectual disability to identify the underlying causative gene. The WES analysis revealed the presence of a homozygous c.740G>A; p.(Arg247Gln) missense SLC25A1 variant, the same SLC25A1 variant as identified in the original family with this phenotype. Electron microscopy of muscle from two cases revealed enlarged and accumulated mitochondria. Haplotype analysis performed in two unrelated families suggested that this variant is a result of recurrent mutation and not a founder effect. This suggests that p.(Arg247Gln) is associated with a relatively mild CMS phenotype with subtle mitochondrial abnormalities, while other variants in this gene cause more severe neurometabolic disease. In conclusion, the p.(Arg247Gln) SLC25A1 variant should be considered in patients presenting with a presynaptic CMS phenotype, particularly with accompanying intellectual disability

Severe neurodevelopmental disease caused by a homozygous TLK2 variant

Abstract: A distinct neurodevelopmental phenotype characterised mainly by mild motor and language delay and facial dysmorphism, caused by heterozygous de novo or dominant variants in the TLK2 gene has recently been described. All cases reported carried either truncating variants located throughout the gene, or missense changes principally located at the C-terminal end of the protein mostly resulting in haploinsufficiency of TLK2. Through whole exome sequencing, we identified a homozygous missense variant in TLK2 in a patient showing more severe symptoms than those previously described, including cerebellar vermis hypoplasia and West syndrome. Both parents are heterozygous for the variant and clinically unaffected highlighting that recessive variants in TLK2 can also be disease causing and may act through a different pathomechanism

Autosomal recessive variants in TUBGCP2 alter the γ-tubulin ring complex leading to neurodevelopmental disease.

Microtubules help building the cytoskeleton of neurons and other cells. Several components of the gamma-tubulin (γ-tubulin) complex have been previously reported in human neurodevelopmental diseases. We describe two siblings from a consanguineous Turkish family with dysmorphic features, developmental delay, brain malformation, and epilepsy carrying a homozygous mutation (p.Glu311Lys) in TUBGCP2 encoding the γ-tubulin complex 2 (GCP2) protein. This variant is predicted to disrupt the electrostatic interaction of GCP2 with GCP3. In primary fibroblasts carrying the variant, we observed a faint delocalization of γ-tubulin during the cell cycle but normal GCP2 protein levels. Through mass spectrometry, we observed dysregulation of multiple proteins involved in the assembly and organization of the cytoskeleton and the extracellular matrix, controlling cellular adhesion and of proteins crucial for neuronal homeostasis including axon guidance. In summary, our functional and proteomic studies link TUBGCP2 and the γ-tubulin complex to the development of the central nervous system in humans

Severe neurodevelopmental disease caused by a homozygous TLK2 variant

Abstract: A distinct neurodevelopmental phenotype characterised mainly by mild motor and language delay and facial dysmorphism, caused by heterozygous de novo or dominant variants in the TLK2 gene has recently been described. All cases reported carried either truncating variants located throughout the gene, or missense changes principally located at the C-terminal end of the protein mostly resulting in haploinsufficiency of TLK2. Through whole exome sequencing, we identified a homozygous missense variant in TLK2 in a patient showing more severe symptoms than those previously described, including cerebellar vermis hypoplasia and West syndrome. Both parents are heterozygous for the variant and clinically unaffected highlighting that recessive variants in TLK2 can also be disease causing and may act through a different pathomechanism

MRI staging of the individual muscles of lower limb for presence of fatty infiltration and myoedema.

<p>MRI staging of the individual muscles of lower limb for presence of fatty infiltration and myoedema.</p

Transversely cut skeletal muscle tissue stained for Haematoxylin and eosin (HE) shows variation in fiber diameter clusters of basophilic regenerating fibers and myophagocytosis.

<p>Immunolabeling to antibodies against dystrophin (dys1,dys2,dys3) sarcoglycans (alpha-A, beta-B, delta-D, gamma-G, merosin, dysferlin (DYSF), caveolin, beta dystroglycan (B-DG), alpha dystroglycan (A-DG) shows uniform labeling along the sarcolemma and positive sarcoplasmic labeling to titin. X400</p

Muscle MRI of patient F97-1.

<p><b>A</b>. T1W image showing global atrophy of muscles of anterior compartment, medial compartment and posterior compartment of thigh. Biceps femoris long head shows stage 3 fatty infiltration. Short head of biceps femoris, sartorius and gracilis are hypertrophied; <b>B</b>. shows severely atrophied vastus intermedius muscle, Mercurie stage 2b infiltration of vastus medialis muscle. Short head of biceps femoris, sartorius and gracilis are hypertrophied; <b>C</b>. Tibilialis anterior, extensor hallucis longus and extensor digitorum longus are atrophied (right more than left). On right side the medial head of gastrocnemius is hypertrophied and lateral head is atrophied. Left soleus is atrophied. Mild fatty infiltration of soleus muscle is noted in left side. Striking asymmetry is present; <b>D</b>. STIR image of thigh shows asymmetrical myoedema pattern. On the right side there is stage 3a myoedema and on the left side it is stage 2a. There is stage 2b myodema noted in the posterior compartment on left side; <b>E</b>. Myoedema mainly seen in gastrocnemius and soleus muscle. Stage 2b on right side and stage 2a on left side.</p

Clinical features and Muscle Histopathology findings of patients with LGMD-2G.

<p>Yrs-Years; F-Female; M-Male; KA-Karnataka; TN-Tamilnadu; AP-Andhra Pradesh; EDB-Extensor digitorumbrevis; TA-Tibialis anterior; CK-Creatine kinase; MDFRS-Muscular dystrophy functional rating scale; Note: Biopsy was not done for patient F111-2 (sibling of patient F111-1).</p

Western blot analysis of telethonin protein in muscle biopsies of control and telethoninopathy patients.

<p><b>A</b>. Telethonin western Blot: Lane C corresponds to non-dystrophic positive control which shows telethonin band at 19 kDa. Lanes 1–7 corresponding to the Telethoninopathy patient samples, shows complete absence of the telethonin band. <b>B</b>. Coomassie stained SDS PAGE (15%) profile of total muscle extract from the samples.</p