16p – Variants

Epidemiology and Etiology:

• 46 cases reported with a similar variant

Common sites:

Gross features:

Histologic features:

Immunophenotype:

Marker:

Sensitivity:

Specificity:

Molecular features:

• Variation in the number of copies of common paralogous gene and pseudogene sequences
• Non-functional paralogous immunoglobin heavy chain segments (paralogous to 14q32.3)
• Pseudogenetic creatine transporter region (16p11.2) related to myosin heavy chain region on Xq28
• Region paralogous to telomeric minisatellite on 6p
• Only visible at the cytogenetic level when copy number is high
• These paralogous regions are thought to be nonfunctional

Other features:

• Counseling dilemma
• A few cases have been associated with abnormality (but others in their families with the same variant were normal)
• Developmental delay
• Dysmorphic features
• Fragile X
• Autism
• Macrocephaly
• Hypospadias
• Heart disease
• Cleft palate
• Infertility, history of miscarriage
• Parental bloods:
• If same variation in normal parent, prognosis is reliably benign

References:

• Lopez Pajares I, Villa O, Salido M, et al. Euchromatic variant 16p+. Implications in prenatal diagnosis. Prenat Diagn. 2006;26(6):535-8.
• Barber JC, Reed CJ, Dajoun SP, Joyce CA. Amplification of a pseudogene cassette underlies euchromatic variation of 16p at the cytogenetic level. Hum Genet. 1999;104(3):211-8.