SYNDACTYLY:
Syndactyly is a congenital anomaly characterized by the partial or complete fusion of two or more digits. It is one of the most frequent anomalies of the hand and foot that occurs during embryonic development due to mutations in the genes responsible for normal digit differentiation. The anomaly occurs in approximately 1 in 2,500 live births, and it is more often noted in males than in females.
This essay will delve into the various types of syndactyly, the genetic mechanisms that underpin its development, the diagnostic approaches, treatment options, and the potential impact of this anomaly on an individual’s quality of life.
Types of Syndactyly:
Syndactyly can be categorized based on the degree of digit fusion, the pattern of affecting digits, and the presence of other associated anomalies. The classification of syndactyly based on fusion degree is as follows:
1. Complete syndactyly: In this type, digits are completely fused with no discrete webbing between them. This can affect all fingers or toes, or just a select few.
2. Incomplete syndactyly: In this type, digit fusion is incomplete with a clear webbing between adjacent digits. This is the most common form of syndactyly.
3. Simple syndactyly: In this type, only the skin and soft tissues between the digits are fused.
4. Complex syndactyly: In this type, bones and joints of adjacent digits are also fused.
Syndactyly can also be classified by pattern, including:
1. Cutaneous syndactyly: This involves fusion of the soft tissue of adjacent digits only.
2. Osseous syndactyly: This involves fusing the bone of adjacent digits, which may include a single, shared phalanx or metacarpal.
3. Polysyndactyly: This form of polydactyly involves duplicate, un-fused or fused digits.
4. Cenani-Lenz syndactyly: In this type, soft tissue and bones are fused, leading to disproportionately short digits.
Associated anomalies and critical syndromes include:
1. Apert syndrome
2. Poland syndrome
3. Holt-Oram syndrome
4. Robinow syndrome
Genetics of Syndactyly
Several genes have been identified as playing a role in the pathogenesis of syndactyly. These include:
1. HOXA and HOXB genes: Hox genes are responsible for controlling development along the anterior-posterior axis of the limb bud. Interestingly, it is the ratio between the extent of HOXA13 and HOXD13 expression that determines the extent of syndactyly.
2. GJA1: The gene encodes connexin 43, a protein that forms gap junctions between cells. Mutations in this gene have been found in several families with syndactyly.
3. LMBR1: This gene encodes a limb developmental protein that is highly conserved across vertebrates. Mutations in this gene have been linked to pre-axial polydactyly and syndactyly.
4. SALL1: This gene is crucial for digit separation, and a gap between the middle digit and the ring finger is maintained by its activity. This gene is implicated in Townes-Brocks syndrome, which is characterized by limb anomalies, imperforate anus, and congenital deafness.
5. GLI3: This gene encodes a transcription factor in the hedgehog signaling pathway. Mutations in this gene have been found in individuals with Greig cephalopolysyndactyly syndrome, which features fused or duplicated digits.
Diagnosis
During prenatal ultrasound screening, syndactyly may be identified as early as 20 weeks of gestation. Postnatally, the diagnosis is based on a combination of clinical examination and radiographic studies. X-rays or computed tomography scans are used to identify fused bones in complex syndactyly, and to delineate any abnormal bone structures. An orthopedic surgeon will examine the extent and type of fusion, and perform a physical examination and review of family history. A genetic consultation may be indicated to target a diagnosis for an underlying genetic defect occurring together with syndactyly. Comprehensive evaluation of both the hand and foot is conducted, with a focus on functional independence, pinch strength, and grasp. In contrast to other developmental malformations of the hand and foot, syndactyly is a very visible deformity, so the psychosocial component of the condition must be acknowledged and evaluated in patients of all ages.
Treatment
The primary aim of treatment is to restore hand and foot function, as well as appearance, and varies according to the type of syndactyly. Simple syndactyly often does not require surgical intervention but may be corrected when the hand or foot is growing to avoid future functional problems. Complex syndactyly requires surgical intervention, typically in early childhood.
