Arrhythmia can be hard to spot in people with TSC, other than by performing routine ECG. For example, arrhythmia may cause fainting that is confused with drop seizures, and symptoms of arrhythmia such as palpitations may not be reported in an individual with developmental delay. Skin
Some form of dermatological sign is present in 96% of individuals with TSC. Most cause no problems, but are helpful in diagnosis. Some cases may cause disfigurement, necessitating treatment. The most common skin abnormalities include:

Hypomelanic macules ("ash leaf spots") are present in about 90% of people with TSC. These small white or lighter patches of skin may appear anywhere on the body, and are caused by a lack of melanin. They are usually the only visible sign of TSC at birth. In fair-skinned individuals, a Woods lamp (ultraviolet light) may be required to see them. On the scalp, the effect may be a white patch of hair (poliosis). Patches smaller than 3mm are known as "confetti" skin lesions. Facial angiofibromas are present in about 75% of people with TSC. These are a rash of reddish spots or bumps on the nose and cheeks in a butterfly distribution, which consist of blood vessels and fibrous tissue. This potentially socially embarrassing rash starts to appear during childhood. Ungual fibromas: Also known as Koenens tumors, these are small fleshy tumors that grow around and under the toenails or fingernails. These are rare in childhood, but common by middle age.
The complex appears to interact with RHEB GTPase, thus sequestering it from activating mTOR signalling, part of the growth factor (insulin) signalling pathway. Thus, mutations at the TSC1 and TSC2 loci result in a loss of control of cell growth and cell division, and therefore a predisposition to forming tumors. TSC affects tissues from different germ layers. Cutaneous and visceral lesions may occur, including angiofibroma, cardiac rhabdomyomas, and renal angiomyolipomas. The central nervous system  lesions seen in this disorder include hamartomas of the cortex, hamartomas of the ventricular walls, and subependymal giant cell tumors, which typically develop in the vicinity of the foramina of Monro.Molecular genetic studies have defined at least two loci for TSC. In TSC1, the abnormality is localized on chromosome 9q34, but the nature of the gene protein, called hamartin, remains unclear. No missense mutations occur in TSC1. In TSC2, the gene abnormalities are on chromosome 16p13. This gene encodes tuberin, a guanosine triphosphatase–activating protein. The specific function of this protein is unknown. In TSC2, all types of mutations have been reported; new mutations occur frequently. Few differences have yet been observed in the clinical phenotypes of patients with mutation of one gene or the other.Cells from individuals with pathogenic mutations in the TSC2 gene display abnormal accumulation of glycogen that is associated with depletion of lysosomes and autophagic impairment.