ClinVar

Description

The heterozygous splice variant c.66463 + 2dupT was detected in the TTN gene, which is found in the literature and the Gene databases dbSNP, ClinVar or HGMD has not yet been reported. According to the calculations of the splice site prediction program varSEAK, the duplication of a T nucleotide leads with a high probability ("risk class 5", highest risk score) to the loss of the 5'-donor-splice-site-motif. Similar gene changes in the TTN gene were described in the HGMD database in patients with muscular dystrophy or restrictive cardiomyopathy [O'Grady (2016) Ann Neurol 80, 101; Kühnisch (2019) Clin Genet 96, 549]. Myopathy refers to diseases that affect skeletal Muscles. These diseases attack muscle fibers, making muscles weak. Inherited myopathies are often caused by inheriting an abnormal gene mutation from a parent that causes the disease. Symptoms of congenital myopathies usually start at birth or in early childhood, but may not appear until the teen years or even later in adulthood. Congenital myopathies are somewhat unique compared with other inherited myopathies, as weakness typically affects all muscles and is often not progressive. Symptoms are: Muscle weakness, most commonly of upper arms and shoulders and thighs, muscle cramps, stiffness and spasms, fatigue with exertion and lack of energy. Our patients all walk on tiptoe, so they show similar symptoms. When we genetically test them with our toe walking panel, we find that around 90 per cent of them have a genetic variant that explains their toe walking. These can be assigned, for example, to the area of myopathies (such as variants of the COL6A3 gene), the area of hereditary neuropathies (such as variants of the KMT2C gene) or the area of metabolic diseases (such as variants of the PYGM gene). In a smaller group of patients with almost identical symptoms, no abnormality is found in the genes of our panel, but spastic paraplegia can be detected. In another small group of our toe walkers, no abnormalities can be detected in the genes analysed in our toe walking panel, nor do they suffer from spastic paraplegia, as is also the case with healthy children. In contrast to these, however, they show a tiptoe gait. These patients suffer from infantile cerebral palsy, in which toe walking can also be observed.