trisomy 20p

The genetic syndrome trisomy 20p (chromosome trisomy 20p) is a congenital chromosomal disorder that causes developmental impairment. Various types of malformations may also occur. This syndrome was first described in 1977 by U. Francke and W. Centerwall. Only about 40 individuals with this syndrome have been described in the available literature.

Trisomy 20p is a chromosomal abnormality resulting from duplication of a portion of the short arm of chromosome 20, with variable length and without recurrent breakpoints. It may occur de novo (as a new genetic change), but most reported cases arise from a reciprocal translocation or, as described in several cases, a parental inversion. Therefore, trisomy 20p is often associated with another chromosomal imbalance, which may alter the clinical presentation.

Pure trisomy 20p resulting from the formation of isochromosomes and whole-arm translocation has also been reported. Precise genotype–phenotype correlations remain unavailable because of the small number of patients and the heterogeneity of breakpoint locations.

Diagnosis:
Diagnosis is based on clinical signs that lead to chromosomal analysis. Depending on their size, partial duplications of chromosome 20p may be diagnosed using conventional or molecular karyotyping. Molecular techniques are required for genetic characterization of the duplication (such as FISH, MLPA, and array CGH).

Approximately one quarter of chromosome abnormalities in trisomy 20p syndrome arise in a germ cell during the formation of reproductive cells. In such cases, the parents have normal chromosomes and the risk of having another child with the syndrome is very low.

If the chromosomal abnormality in the child is caused by a balanced translocation in one of the parents, there is a risk of recurrence in a future pregnancy.

Treatment:
At birth, children with the syndrome usually have normal weight and length, but they often have low muscle tone and joint laxity. They may have difficulty sucking/feeding.

About one quarter of affected children have a congenital heart defect. Some may have Tetralogy of Fallot, a combination of four different heart defects, or another severe cardiac malformation.

Kidney malformations occur in approximately one in four children with the syndrome. Other common defects are congenital and may include abnormalities involving the nipples and lungs.

The prognosis is variable and depends on the size and location of the duplication, as well as the quality and timing of treatment. Exact life expectancy is unknown and depends on whether severe congenital anomalies are present. However, most individuals survive into adulthood (and may reach old age).

Treatment is symptomatic, meaning it focuses on managing the individual symptoms and complications rather than curing the condition itself.

• delayed psychomotor development
• mild to moderate intellectual disability
• poor motor coordination
• marked speech delay
• difficulty articulating certain sounds
• round (full) face
• thick (usually straight) hair
• arched lateral eyebrows
• widened nostrils
• high-arched palate
• abnormal teeth
• large ears
• skeletal anomalies (fusion of vertebrae, reduced intervertebral disc spaces, spina bifida, scoliosis, kyphosis)
• hip deformity
• osteoporosis in some patients
• sometimes congenital heart defects
• normal birth weight and growth
• less commonly umbilical or inguinal hernia and hypospadias