Skin may be dry and coarse, excessively wrinkled around the face and loose around the hands yet tight around the finger joints, leading to diminished use of the fingers.Genital defects may include: ambiguous genitalia, a displaced and/or atypically small penis (micropenis), an absent scrotum around the testes and undescended testicles. Finally, alopecia and thin, sparse hair are also frequently observed. Causes
Like Barber–Say syndrome, AMS is caused by mutations in the TWIST2 gene that affect a highly conserved residue of TWIST2 (twist-related protein 2). TWIST2 is a basic helix-loop-helix transcription factor that binds to E-box DNA motifs (5-CANNTG-3) as a heterodimer and inhibits transcriptional activation. Because TWIST2 mediates mesenchymal stem cell differentiation and prevents premature or ectopic osteoblast differentiation, mutations in TWIST2 that disrupt these functions by altering DNA-binding activity could explain many of the phenotypes of AMS. Current research points to the substitution of the wild-type amino acid for Lysine at TWIST2 residue 75 as a significant genetic cause of AMS.AMS is inherited in an autosomal dominant manner, in which an affected individual needs only one copy of the mutant allele in order to express the disease. Mechanism
The mesenchyme is a mesodermal embryonic tissue that can develop into a multitude of different tissues depending on the needs of the developing embryo. The mesenchyme can develop into blood, cartilage, and membranes. In a normal patient, TWIST2 is highly expressed during embryonic development, specifically in the craniofacial development and chondrogenisis.
Ablepharon macrostomia syndrome (AMS) is an extremely rare, autosomal dominant genetic disorder characterized by abnormal phenotypic appearances that primarily affect the head and face as well as the skull, skin, fingers and genitals. AMS generally results in abnormal ectoderm-derived structures. The most prominent abnormality is the underdevelopment (microblepharon) or absence of eyelids – signifying the ablepharon aspect of the disease – and a wide, fish-like mouth – macrostomia. Infants presenting with AMS may also have malformations of the abdominal wall and nipples. Children with AMS might also experience issues with learning development, language difficulties and intellectual disabilities. AMS is caused by mutations in the TWIST2 gene, among others. It is closely related to Barber–Say syndrome in terms of phenotypic abnormalities. Signs and symptoms
AMS is generally characterized by abnormal appearances of the skin, eyes, fingers, genitals, head and face. Infants with AMS will have thin, redundantly wrinkled skin and excessive facial creases; wide-set eyes with absent or severely underdeveloped eyelids and down-turned lower eyelids; and a wide, fish-like mouth that may be fused together at the corners. Other appearances of the face and head include: broad nasal bridge, wide, flared nostrils and thick and flared alae nasi (edges of the nostrils).Abnormalities can also be seen in the hands and fingers, as infants with AMS will also have webbed fingers with limited ability to flex and extend the fingers. Infants with AMS will also display small, rudimentary ears that are atypically low-set on the skull. Absence of the zygomatic bone is also possible.