TBS and ZLS form a spectrum, and it is not always possible to predict where on that spectrum a child may fit. Children with both conditions are often happy and playful. Those with TBS have profound developmental delay, which means that they are unlikely to ever live independently. Children ZLS may have normal development and will possibly be able to live independently. Epilepsy can be seen in both conditions.
Children with TBS have ‘droopy’ facial features, while those with ZLS tend to have coarsened features. Children with ZLS also have increased body hair (‘hirsutism’) and their doctor may discover that some abdominal organs are enlarged, such as the liver and spleen. In both conditions, children develop an overgrowth of the gums. They are also frequently missing the nails on the thumbs and great toes. Other nails may appear small as well.
Both conditions are incredibly rare, and no one knows exactly how prevalent either is. Neither TBS nor ZLS tend to be inherited. They arise as a result of a new gene error. There is nothing that either parent did to make this error occur. If a person with either TBS or ZLS were to have children of their own, however, the chance of their offspring being affected is 50% in each pregnancy.
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