47,XYY syndrome, also called XYY syndrome or Jacobs syndrome
Is a sex chromosome aneuploidy in which a male has an extra Y chromosome.
• Karyotype: 47,XYY
• Phenotypic sex: Male
• Characterized by:
o Tall stature, Variable speech and learning difficulties
o Normal puberty and sexual development
o Usually normal fertility
Epidemiology - Incidence: Approximately 1 in 1,000 live male births
Cause - Usually results from paternal meiotic nondisjunction, most often during meiosis II, producing a YY sperm.
Pathophysiology - The additional Y chromosome increases the dosage of genes that are not subject to X-inactivation, particularly genes in the pseudoautosomal regions.
Effects include:
• Increased linear growth
• Variable neurodevelopmental differences
• No major impairment of testicular function in most individuals
Clinical Features - The phenotype is highly variable, and many individuals have no significant medical problems.
Infancy
• Mild hypotonia, Delayed motor milestones
• Feeding difficulties
Childhood
• Tall stature, Speech and language delay
• Learning difficulties, Mild motor coordination problems
• Fine motor delay
Behavioral Features
• ADHD, Impulsivity
• Emotional immaturity, Anxiety
• Social communication difficulties
• Autism spectrum disorder
Adolescence
• Normal puberty, Normal secondary sexual characteristics
• Increased height, Acne may be more common
Adults
• Normal sexual development, Normal libido
• Normal testosterone levels, Independent living
• Employment, Normal family life
Physical Examination
• Tall stature (often above the 75th percentile)
• Long limbs
• Mild hypotonia
Endocrine and Reproductive Features
Puberty
• Normal onset, Normal progression
Testes
• Normal size, Normal function
Fertility
• Usually normal, Most men can father children naturally
• Infertility is uncommon but has been reported in a minority.
Associated Conditions
Compared with the general population, there is an increased frequency of:
• Speech and language disorders, Learning disabilities
• ADHD, Autism spectrum disorder
• Tremor, Motor coordination difficulties
