What may cause a child to have both severe cognitive delay and always happy demeanor but not Angelman syndrome?

There are several genetic conditions and disorders that may cause a child to have both severe cognitive delay and always happy demeanor but not Angelman syndrome. Here are some possible causes:

1. Down syndrome: Down syndrome is a genetic disorder caused by the presence of an extra copy of chromosome 21. It can lead to intellectual disability, developmental delays, and characteristic facial features. Children with Down syndrome often have a cheerful and friendly demeanor.

2. Williams syndrome: Williams syndrome is a rare genetic disorder caused by a deletion in chromosome 7. It is characterized by distinctive facial features, cardiovascular problems, and intellectual disability. Children with Williams syndrome are typically very friendly, outgoing, and have a musical aptitude.

3. Prader-Willi syndrome: Prader-Willi syndrome is a genetic disorder caused by a deletion or abnormality in chromosome 15. It leads to intellectual disability, growth problems, and an insatiable appetite. Children with Prader-Willi syndrome often exhibit a happy and affectionate disposition.

4. Fragile X syndrome: Fragile X syndrome is a genetic disorder caused by a mutation in the FMR1 gene. It is the most common inherited cause of intellectual disability. Children with Fragile X syndrome may have cognitive delays, behavioral problems, and social difficulties. However, they often have a friendly and affectionate nature.

5. Smith-Magenis syndrome: Smith-Magenis syndrome is a genetic disorder caused by a deletion in chromosome 17. It is characterized by intellectual disability, behavioral problems, and distinct physical features. Children with Smith-Magenis syndrome may exhibit a happy and outgoing demeanor.

It's important to note that these are just a few possible causes, and a proper diagnosis by a medical professional is necessary to determine the specific underlying condition in a child with severe cognitive delay and a happy demeanor. Genetic testing and evaluation by specialists can help identify the specific genetic abnormality or disorder responsible for the child's symptoms.