Spider Baby

Spider Baby is a 1968 black comedy horror film, written and directed by Jack Hill. It stars Lon Chaney Jr. as Bruno, the chauffeur and caretaker of three orphaned siblings who suffer from "Merrye Syndrome", a genetic condition starting in early puberty that causes them to regress mentally, socially and physically.

Plot
The story follows a family of inbreeds who have been afflicted by a genetic disorder known as 'Merrye syndrome', named after the family in which the disorder developed. This malady causes its victims to enter a state of age regression that starts at the age of ten and continues throughout the remainder of the person's life, rendering them with the intelligence of a child. The final generation of the family has been entrusted to the care of the family chauffeur (Lon Chaney Jr), and all is well for these odd people until a greedy branch of the family decides that they want to relieve the family of its home. Mental illness has always, and will always be, a fascinating subject for horror movies as it probes into the unknown and Spider Baby makes best use of that fact.