| Polysyndactyly | |
|---|---|
 | |
| Foot polysyndactyly | |
| Specialty | Medical genetics |
Polysyndactyly is a congenital anomaly, combining polydactyly and syndactyly, in which affected individuals have an extra finger or toe that is connected, via fusing or webbing, to an adjacent digit. [1] [2]
Presentations of polysyndactyly vary in location and size of the duplicated digit, and in the extent of webbing between digits. [2] [3] [4]
The extra digit is most commonly postaxial [5] , on the same side as the pinky or little toe. [3] Preaxial polysyndactyly, in which the duplicated digit is on the side of the thumb or big toe, is less common. [3] Crossed polysyndactyly, in which polysyndactyly is present on the hand and foot, and is preaxial on one and postaxial on the other, is extremely rare and often occurs with other genetic disorders. [6]
Polysyndactyly may be classified by the level of duplication. The extra digit may be small and comprise only soft tissue, [7] but usually includes at least one bone, most commonly the distal and middle phalanges. [4] [8] Partial or complete duplication of the proximal phalanx, metacarpal or metatarsal can also occur. [4] [7]
Fusing of the extra digit may be incomplete [4] , giving the appearance of the extra digit being partially connected to the (otherwise normal) adjacent digit. However, complete fusion of the extra digit to the adjacent digit, via soft tissue and skin, is more common. [4]
Polysyndactyly is typically inherited, in an autosomal dominant pattern [2] [6] [9] . The specific mutations leading to polysyndactyly are varied between among types of the condition and different families. However, many cases are caused by changes to genetic elements affecting the signaling molecule Sonic Hedgehog (SHH). Primarily, mutations are found in the zone of polarizing activity regulatory sequence, or ZRS, that controls the expression of SHH in developing limbs. Many cases of polysyndactyly are the result of duplications of the ZRS [10] [11] [12] or the nearby pre-ZRS region. [13] [14]
Polysyndactyly can be associated with the presence of other genetic disorders. It is a hallmark of Carpenter's syndrome, an autosomal recessive disorder that is also associated with craniosynostosis, obesity, short stature, and other malformations [15] . Patients with other syndromes, including Pallister-Hall syndrome [16] and Greig cephalopolysyndactyly syndrome [17] may also display polysyndactyly of varying severity.
Polysyndactyly has full penetrance but variable expressivity; individuals who possess an allele for polysyndactyly may have a different severity of the condition. This has been seen in case studies where a parent has hexadactyly in their 4th and 5th fingers but their child has hexadactyly in their 1st, 2nd, 3rd and 4th fingers. [18]
Polysyndactyly can be diagnosed in utero through sonographic and genetic testing, though sonography may be preferred due to the cost and risk associated with genetic testing. [19] Ultrasounds, typically done at the 14th to 16th week of pregnancy, can detect the presence of extra metacarpals, metatarsals, or phalanges. [19] [20] Genetic testing of the fetus examines disruptions in the HOXD13 gene at 2q31-q32 and in the GLI3 gene at 7p13. These genomic regions regulate proliferation and differentiation in the limb bud, and can lead to phenotypic anomalies, including polysyndactyly, if mutated. Postnatally, polysyndactyly is diagnosed by observation of an extra digit and X-rays to confirm the presence of an extra metacarpal, metatarsal, or phalanx. [19] [21]
Polysyndactyly is treated through surgical excision of the extra digit. The choice of which digit to remove affects post-operative outcomes; factors that must be considered when determining which digit to excise include the neurovascular bundles, angle differences, risks for impaired circulation, post-operative appearance, and residual deformities. [5] [7]
Treatment is generally aimed at normalizing both function and appearance of the affected extremity [3] and, in the case of polysyndactyly of the foot, shoe fit and comfort [22] . The underlying cause of polysyndactyly determines the overall quality of life for individuals diagnosed with this condition. If there are no comorbid or underlying genetic conditions, surgical removal of the extra digit generally results in a high quality of life. Parents of children with polysyndactyly have reported high physical, social, emotional, and school functioning and good psychosocial health after removal of the extra digit. [23]
Polydactyly or polydactylism, also known as hyperdactyly, is an anomaly in humans and animals resulting in supernumerary fingers and/or toes. Polydactyly is the opposite of oligodactyly.
Syndactyly is a condition wherein two or more digits are fused together. It occurs normally in some mammals, such as the siamang and diprotodontia, but is an unusual condition in humans. The term is from Greek σύν, syn 'together' and δάκτυλος, daktulos 'finger'.
Carpenter syndrome, also called acrocephalopolysyndactyly type II, is an extremely rare autosomal recessive congenital disorder characterized by craniofacial malformations, obesity, syndactyly, and polydactyly. Acrocephalopolysyndactyly is a variation of acrocephalosyndactyly that presents with polydactyly.
A polydactyl cat is a cat with a congenital physical anomaly called polydactyly, which causes the cat to be born with more than the usual number of toes on one or more of its paws. Cats with this genetically inherited trait are most commonly found along the East Coast of North America and in South West England and Wales.
Zinc finger protein GLI3 is a protein that in humans is encoded by the GLI3 gene.
Greig cephalopolysyndactyly syndrome is a disorder that affects development of the limbs, head, and face. The features of this syndrome are highly variable, ranging from very mild to severe. People with this condition typically have one or more extra fingers or toes (polydactyly) or an abnormally wide thumb or big toe (hallux).
Duane-radial ray syndrome, also known as Okihiro Syndrome, is a rare autosomal dominant disorder that primarily affects the eyes and causes abnormalities of bones in the arms and hands. This disorder is considered to be a SALL4-related disorder due to the SALL4 gene mutations leading to these abnormalities. It is diagnosed by clinical findings on a physical exam as well as genetic testing and imaging. After being diagnosed, there are other evaluations that one may go through in order to determine the extent of the disease. There are various treatments for the symptoms of this disorder.
Acrocallosal syndrome is an extremely rare autosomal recessive syndrome characterized by corpus callosum agenesis, polydactyly, multiple dysmorphic features, motor and intellectual disabilities, and other symptoms. The syndrome was first described by Albert Schinzel in 1979. Mutations in KIF7 are causative for ACLS, and mutations in GLI3 are associated with a similar syndrome.
Acropectoral syndrome is an autosomal dominant skeletal dysplasia syndrome affecting the hands, feet, sternum, and lumbosacral spine. A recently proposed candidate gene for preaxial polydactyly is LMBR1, encoding a novel transmembrane receptor, which may be an upstream regulator of SHH. The LMBR1 gene is on human chromosome 7q36.
Triphalangeal thumb (TPT) is a congenital malformation where the thumb has three phalanges instead of two. The extra phalangeal bone can vary in size from that of a small pebble to a size comparable to the phalanges in non-thumb digits. The true incidence of the condition is unknown, but is estimated at 1:25,000 live births. In about two-thirds of the patients with triphalangeal thumbs, there is a hereditary component. Besides the three phalanges, there can also be other malformations. It was first described by Columbi in 1559.
Ectrodactyly, split hand, or cleft hand involves the deficiency or absence of one or more central digits of the hand or foot and is also known as split hand/split foot malformation (SHFM). The hands and feet of people with ectrodactyly (ectrodactyls) are often described as "claw-like" and may include only the thumb and one finger with similar abnormalities of the feet.
Young–Madders syndrome, alternatively known as Pseudotrisomy 13 syndrome or holoprosencephaly–polydactyly syndrome, is a genetic disorder resulting from defective and duplicated chromosomes which result in holoprosencephaly, polydactyly, facial malformations and intellectual disability, with a significant variance in the severity of symptoms being seen across known cases. Many cases often suffer with several other genetic disorders, and some have presented with hypoplasia, cleft lip, cardiac lesions and other heart defects. In one case in 1991 and another in 2000 the condition was found in siblings who were the product of incest. Many cases are diagnosed prenatally and often in siblings. Cases are almost fatal in the prenatal stage with babies being stillborn.
Filippi syndrome, also known as Syndactyly Type I with Microcephaly and Mental Retardation, is a very rare autosomal recessive genetic disease. Only a very limited number of cases have been reported to date. Filippi Syndrome is associated with diverse symptoms of varying severity across affected individuals, for example malformation of digits, craniofacial abnormalities, intellectual disability, and growth retardation. The diagnosis of Filippi Syndrome can be done through clinical observation, radiography, and genetic testing. Filippi Syndrome cannot be cured directly as of 2022, hence the main focus of treatments is on tackling the symptoms observed on affected individuals. It was first reported in 1985.
Polyonychia also known as supernumerary nails is a condition in which two or more nails grow in the same finger or toe.
Familial opposable triphalangeal thumb duplication is a limb malformation syndrome and a type of pre-axial polydactyly, characterized by having duplicated opposable triphalangeal thumbs. This condition can be a symptom of other genetic disorders, such as Holt–Oram syndrome and Fanconi anemia. This trait is autosomal dominant and often runs in families. Sometimes big toe duplication, post-axial polydactyly, and syndactyly of the hand and feet can occur alongside this malformation Approximately 20 families with the condition have been described in medical literature.
Tibial hemimelia-polysyndactyly-triphalangeal thumb syndrome is a rare genetic limb malformation syndrome which is characterized by thumb triphalangy, polysyndactyly of the hand and foot, and hypoplasia/aplasia of the tibia bone. Additional features include short stature, radio-ulnar synostosis, ectrodactyly and abnormalities of the carpals and metatarsals. Only 19 affected families worldwide have been recorded in medical literature. It is associated with a heterozygous base pair substitution of A to G in position 404–406, located on intron 5 in the LMBR1 gene.
Aphalangy-syndactyly-microcephaly syndrome is a very rare limb malformation syndrome which is characterized by agenesis of the distal phalanges, syndactyly, duplication of the fourth metatarsal, microcephaly, and mild intellectual disabilities. Only 6 cases from 4 families in Spain, Turkey and other countries have been reported in medical literature. Transmission is autosomal dominant.
Metacarpal synostosis is a rare congenital difference which is characterized by the fusion of 2 metacarpals of the hand, which are usually shortened. It is most commonly seen as a fusion of the 4th and 5th metacarpals. It is a type of non-syndromic syndactyly/synostosis. Autosomal dominant and X-linked recessive inheritance patterns have been reported.
Triphalangeal thumbs-brachyectrodactyly syndrome is a very rare limb malformation syndrome of genetic origin which is characterized by polydactyly, syndactyly, brachydactyly, ectrodactyly, triphalangeal thumb and polyphalangism. Onychodystrophy and anonychia are also seen often. 27 cases from seven families from Mexico and the United States have been described in medical literature. It is inherited in an autosomal dominan manner and thought to be caused by mutations in the HOXD13 gene, in chromosome 2.
Brachydactyly-preaxial hallux varus syndrome, also known as 'Christian brachydactyly, is a rare congenital and genetic limb malformation syndrome which is characterized by hallux varus, brachydactyly type D and Morton's toe, alongside the adduction of said digits. Intellectual disabilities have also been reported. 10 cases have been described in medical literature.
 | This genetic disorder article is a stub. You can help Wikipedia by expanding it. |