MedGen

Neurodevelopmental disorder with hypotonia, language delay, and skeletal defects with or without seizures (NEDHLSS) is characterized by global developmental delay apparent from infancy. Affected individuals show severe hypotonia with delayed walking or inability to walk, poor or absent speech, and impaired intellectual development with behavioral abnormalities. Most patients have early-onset seizures, mild skeletal defects that are usually distal, and nonspecific dysmorphic features. More severely affected individuals have additional congenital abnormalities; however, cardiac involvement is rare (summary by Rodan et al., 2021). [from OMIM]

The first identified CACNA1C-related disorder, referred to as Timothy syndrome, consists of the combination of prolonged QT interval, autism, and cardiovascular malformation with syndactyly of the fingers and toes. Infrequent findings also include developmental and speech delay, seizures, and recurrent infections. With increased availability of molecular genetic testing, a wider spectrum of pathogenic variants and clinical findings associated with CACNA1C-related disorders has been recognized. Because CACNA1C is associated with calcium channel function, all individuals with a pathogenic variant in this gene are at risk for cardiac arrhythmia of a specific type. The clinical manifestations of a CACNA1C-related disorder include three phenotypes: Timothy syndrome with or without syndactyly. QT prolongation (QTc >480 ms) and arrhythmias in the absence of other syndromic features. Short QT syndrome (QTc <350 ms) or Brugada syndrome with short QT interval. These three phenotypes can be separated into two broad categories on the basis of the functional consequences of the pathogenic variants in CACNA1C: QT prolongation with or without a Timothy syndrome-associated phenotype associated with pathogenic variants inducing a gain of function at the cellular level (i.e., increased calcium current). Short QT interval with or without Brugada syndrome EKG pattern associated with pathogenic variants causing loss of function (i.e., reduced calcium current). [from GeneReviews]

Brugada syndrome is characterized by cardiac conduction abnormalities (ST segment abnormalities in leads V1-V3 on EKG and a high risk for ventricular arrhythmias) that can result in sudden death. Brugada syndrome presents primarily during adulthood, although age at diagnosis may range from infancy to late adulthood. The mean age of sudden death is approximately 40 years. Clinical presentations may also include sudden infant death syndrome (SIDS; death of a child during the first year of life without an identifiable cause) and sudden unexpected nocturnal death syndrome (SUNDS), a typical presentation in individuals from Southeast Asia. Other conduction defects can include first-degree AV block, intraventricular conduction delay, right bundle branch block, and sick sinus syndrome. [from GeneReviews]

The first identified CACNA1C-related disorder, referred to as Timothy syndrome, consists of the combination of prolonged QT interval, autism, and cardiovascular malformation with syndactyly of the fingers and toes. Infrequent findings also include developmental and speech delay, seizures, and recurrent infections. With increased availability of molecular genetic testing, a wider spectrum of pathogenic variants and clinical findings associated with CACNA1C-related disorders has been recognized. Because CACNA1C is associated with calcium channel function, all individuals with a pathogenic variant in this gene are at risk for cardiac arrhythmia of a specific type. The clinical manifestations of a CACNA1C-related disorder include three phenotypes: Timothy syndrome with or without syndactyly. QT prolongation (QTc >480 ms) and arrhythmias in the absence of other syndromic features. Short QT syndrome (QTc <350 ms) or Brugada syndrome with short QT interval. These three phenotypes can be separated into two broad categories on the basis of the functional consequences of the pathogenic variants in CACNA1C: QT prolongation with or without a Timothy syndrome-associated phenotype associated with pathogenic variants inducing a gain of function at the cellular level (i.e., increased calcium current). Short QT interval with or without Brugada syndrome EKG pattern associated with pathogenic variants causing loss of function (i.e., reduced calcium current). [from GeneReviews]