Dysmelia

Piglet with dipygus at Ukrainian National Chernobyl Museum in Kiev

Dysmelia, derived from the Greek words "δυσ-" (dys, meaning "bad") and "μέλ|ος" (mél|os, meaning "limb"), is a congenital disorder characterized by limb anomalies. These limb irregularities can manifest as missing, malformed, or supernumerary limbs. Understanding the types, causes, and epidemiology of dysmelia aids in the clinical management and genetic counseling of affected individuals.

Classification

Dysmelic conditions can be broadly categorized based on the presentation of the limb irregularities:

• Missing Limbs:
• * Amelia: Absence of a limb or limbs.
• * Oligodactyly: Fewer than the normal number of fingers or toes.
• * Congenital amputation: Limb loss present at birth.
• Malformation of Limbs:
• * Ectrodactyly: Split or cleft hand/foot, colloquially referred to as "lobster claw hand."
• * Phocomelia: Shortened, poorly formed limb, often resembling a flipper.
• * Meromelia: Partial absence of a limb segment.
• * Syndactyly: Fused fingers or toes.
• * Brachydactyly: Shortened fingers or toes.
• * Club foot: Foot twisted out of shape or position.
• Supernumerary Limbs:
• * Polymelia: Presence of additional limbs.
• * Polydactyly: Extra fingers or toes.
• * Polysyndactyly: Combination of fused and extra digits.

Epidemiology

Limb developmental anomalies, encapsulated under dysmelia, occur in approximately 1 in 1,000 births.

Etiology

The causes of dysmelia are multifaceted and can be classified into genetic and environmental factors:

• Genetic Factors:
• * Hereditary transmission of specific genes, leading to conditions such as polydactyly, ectrodactyly, or brachydactyly. Often, these limb deformities may present along with other symptoms as part of a broader syndrome.
• Environmental Factors:
• * Amniotic Band Syndrome: Fibrous bands in the uterus can constrict a developing limb, leading to congenital amputation or other deformities.
• * Teratogens: Certain drugs, such as thalidomide, when taken during pregnancy can induce phocomelia.
• * Environmental Chemicals: Exposure to certain chemicals during fetal development can disrupt limb formation.
• * Ionizing Radiation: Exposure to nuclear weapons, radioiodine, or radiation therapy during pregnancy can adversely impact limb development.
• * Infections: Certain infections during pregnancy can interfere with fetal limb development.
• * Metabolic Imbalance: Disruptions in the mother's metabolic balance can lead to developmental anomalies in the fetus.

Conclusion

Dysmelia encompasses a broad spectrum of limb developmental disorders that can have significant clinical and psychosocial impacts. A comprehensive understanding of its classifications and etiologies aids clinicians in diagnosis, management, and counseling.