The Medical World of Joseph Briteman

On a more serious note, Joseph Briteman is afflicted with a variety of mental and physical challenges. Physically, he has inherited the condition, Neurofibromatosis, sometimes called elephantiasis or Recklinghausen’s disease, and mentally he struggles with ( IDD ), an intellectual developmental disability.
Most people are aware of the physical deformation in association with the Elephant Man, Joseph Merrick, who was not at all mentally impaired. 

Webster’s Medical Dictionary describes Neurofibromatosis 
as having two types - 

neurofibromatosis 1  :  an inherited developmental disorder characterized especially by brown spots on the skin that are typically present at birth, neurofibromas of peripheral nerves, and deformities of subcutaneous tissues and bone—abbreviation NF, NF-1; called also Recklinghausen's disease, von Recklinghausen's disease

neurofibromatosis type 2  or neurofibromatosis 2  :  an inherited disorder characterized by bilateral acoustic neuromas developing in childhood or early adulthood that are typically accompanied by other nonmalignant tumors of the central nervous system—abbreviation NF, NF-2  ◆Both types of neurofibromatosis are inherited as an autosomal dominant trait requiring that one parent pass on a copy of the defective gene on a chromosome other than a sex chromosome. Type 1 is much more common than type 2.

( IDD ) intellectual developmental disability
also known as mental retardation.

A clinical description is as follows - 

...behavioural traits associated with MR (but not deemed criteria for an MR diagnosis) include aggression, dependency, impulsivity, passivity, self-injury, stubbornness, low self-esteem, and low frustration tolerance. Some may also exhibit mood disorders such as psychotic disorders and attention difficulties, though others are pleasant, otherwise healthy individuals. Sometimes physical traits, like shortness in stature and malformation of facial elements, can set individuals with MR apart, while others may have a normal appearance.

Mental retardation affects about 1 percent to 3 percent of the population.