The 11q deletion, also known as Jacobsen syndrome or 11q terminal deletion disorder, is a rare chromosomal anomaly involving chromosome 11. This genetic change, where a segment of genetic material is missing, can lead to various health and developmental challenges. It occurs in approximately 1 in 100,000 newborns and is more frequently observed in girls than in boys, with a female-to-male ratio of 2:1.
Understanding 11q Deletion
Each chromosome has a short arm (“p”) and a long arm (“q”). In 11q deletion, a portion of the long arm of chromosome 11 is missing. This loss of genetic material occurs at the very end, or terminus, of the q arm, leading to the name 11q terminal deletion disorder.
The size of the deleted segment on chromosome 11 varies significantly among individuals, ranging from 7 to 16 million DNA base pairs. This variability influences the number of genes affected and the range and severity of observable characteristics. For instance, a smaller deletion might result in a “partial Jacobsen syndrome” phenotype with less severe symptoms.
Most 11q deletion cases arise as a new, spontaneous event during reproductive cell formation or early fetal development. In about 85% of families, both parents have normal chromosomes, and the deletion has a very low likelihood of recurrence in future pregnancies. However, in a smaller percentage of cases, the deletion can be inherited from a parent who carries a balanced chromosomal rearrangement, which can lead to an unbalanced deletion in the offspring.
Recognizing the Characteristics
Individuals with 11q deletion present with a range of distinctive physical and developmental characteristics, though their severity varies widely. Developmental delays are common, affecting motor skills like sitting, standing, and walking, as well as speech and cognitive abilities. Most individuals experience intellectual disability, ranging from mild to moderate, though some may have normal to borderline intelligence.
Distinctive facial features are frequently observed. These include a small head (microcephaly) or a pointed forehead (trigonocephaly), widely spaced eyes (hypertelorism) with droopy eyelids (ptosis), and skin folds at the inner corner of the eyes (epicanthal folds). Individuals may also have a broad nasal bridge, a small lower jaw, a thin upper lip, and downturned corners of the mouth.
The deletion can also affect multiple body systems. Congenital heart defects are common, including underdevelopment of the left side of the heart. Over 90% of individuals have Paris-Trousseau syndrome, a bleeding disorder affecting platelets that leads to a lifelong risk of abnormal bleeding and easy bruising.
Other health concerns include kidney abnormalities, gastrointestinal issues like chronic constipation or pyloric stenosis, and a higher susceptibility to infections due to immune system deficiencies. Skeletal abnormalities, frequent ear and sinus infections, and problems with vision and hearing are also common.
Diagnosis and Genetic Counseling
Diagnosis of 11q deletion often begins with clinical findings, such as characteristic physical features and developmental delays. Confirmation typically involves genetic testing. Chromosomal microarray analysis (CMA) is a primary method used to detect these deletions, as it identifies missing or duplicated DNA segments too small for traditional karyotyping. Fluorescence in situ hybridization (FISH) is another technique that confirms the deletion by using fluorescent probes to highlight specific chromosomal regions.
Genetic testing can be performed after birth, usually through a blood sample. Prenatal diagnosis is also possible, particularly if concerns arise from early pregnancy ultrasounds showing features like nuchal thickening or heart anomalies. Invasive procedures like amniocentesis or chorionic villus sampling (CVS) can then be performed, with genetic material analyzed using array comparative genomic hybridization. Non-invasive prenatal testing (NIPT) from a maternal blood sample may indicate an increased chance of the deletion, but an invasive procedure is recommended for definitive confirmation.
Following a diagnosis, genetic counseling is an important step for affected individuals and their families. Genetic counselors provide detailed information about the condition, including its specific implications for health and development. They also discuss the likelihood of recurrence in future pregnancies, explaining whether the deletion was a spontaneous event or inherited. For families where a parent carries a balanced translocation, the recurrence risk is higher, and counselors can outline options for family planning.
Supportive Care and Management
Ongoing care for individuals with 11q deletion involves a multidisciplinary approach, focusing on managing symptoms and supporting development. Early intervention programs are beneficial, offering therapies tailored to individual needs. Physical therapy helps address gross motor delays, aiding in skills like walking and overall mobility, and can involve adaptive equipment. Occupational therapy focuses on fine motor skills and daily living activities, promoting greater independence. Speech therapy supports language development and communication skills, which are often delayed.
Educational support is also an important part of management, particularly for individuals experiencing learning difficulties. Special education programs can provide accommodations and strategies to enhance learning. A team of medical specialists typically works together to address the diverse health concerns associated with 11q deletion. This team may include:
- Cardiologists for heart defects.
- Neurologists for brain anomalies or seizures.
- Developmental pediatricians to oversee overall development.
- Hematologists for Paris-Trousseau syndrome, which may require medication or blood transfusions.
- Immunologists to manage recurrent infections and potential immune deficiencies.
This coordinated care aims to create an individualized care plan that addresses each person’s unique challenges, helping them reach their full potential.