December 21, 2020
Years published: 1995, 2004, 2017, 2020
NORD gratefully acknowledges Dr. Renita Castelino, Department of Oral Medicine and Radiology, NITTE University, Mangalore, India, for assistance in the preparation of this report.
Hanhart syndrome is a rare condition characterized by a short, incompletely developed tongue (hypoglossia); absent or partially missing fingers and/or toes (hypodactylia); malformed arms and/or legs (peromelia); and an extremely small jaw (micrognathia).The severity of these physical abnormalities varies greatly from person to person. Children with this disorder often have some, but not all, of these symptoms. The cause of Hanhart syndrome is not fully understood.
Hanhart syndrome is in the group of conditions known as oromandibular-limb hypogenesis syndromes (OLHS). These syndromes are characterized by underdevelopment of the limbs, mouth and jaw.
Hanhart syndrome was first described in 1932. In 1950, Dr. Hanhart described three children who had a missing tongue with associated limb defects and the name ‘Hanhart syndrome’ was adopted.
The craniofacial abnormalities in children with Hanhart syndrome can include a small mouth (microstomia); small jaw and deeply receding jaw (micrognathia); shorty, incompletely developed tongue (hypoglossia); cleft palate; cleft tongue; broad nose; increased distance between the inner corners of the eyelids (telecanthus); lower eyelid defects; facial asymmetry; and partial absence of the jaw (mandibular hypodontia).
Affected children may have fingers and/or toes that are partially missing or completely absent (ectrodactylia). In addition, lower (distal) portions of the arms and/or legs may be malformed, partially missing, and/or completely absent (amelia). Limb malformations may vary in severity from limb to limb (asymmetric).
Infants with Hanhart syndrome may have loss of some motor function (paralysis) in the facial area at birth due to impairment of one or more of the 12 nerve pairs that arise from the brain (cranial nerve palsy). In many cases, congenital nerve palsy of the 6th (abducens) and/or 7th (facialis) cranial nerves is present. In rarer cases, the 3rd (oculomotorius), 5th (trigeminus), 9th (glossopharyngeus), and/or 12th (hypoglossus) cranial nerves are affected. The presence of some of these nerve palsies can worsen any feeding problems that occur because of tongue, mouth, and/or jaw abnormalities.
Additional abnormalities may occur in association with Hanhart syndrome. In some affected individuals, the spleen and the gonads (i.e., testes in males, ovaries in females) may have fused together during fetal development (splenogonadal fusion). This may be manifested in males as a testicular mass or as a testis that has failed to descend into the scrotum (cryptorchidism). Some individuals may have vertical skin folds that cover the inner corners of the eyes (epicanthus); a malformation of the foot (clubfoot or talipes); an absent kidney (unilateral renal agenesis); a cyst in the brain (porencephalic cyst); and/or an absent or abnormally located anus (imperforate anus). Obstruction of the central portion of the small intestine (jejunal atresia) may occur due to twisting of the small intestine.
Intellectual disability may be present in some individuals with Hanhart syndrome.
The exact cause of Hanhart syndrome is not known. Cases tend to occur randomly, with no apparent cause (sporadic). Some researchers believe that the disorder, which has been reported in the children of blood relatives (consanguinity) in a number of cases, may be inherited in an autosomal recessive pattern.
Recessive genetic disorders occur when an individual inherits two copies of an abnormal gene for the same trait, one from each parent. If an individual inherits one normal gene and one gene for the disease, the person will be a carrier for the disease but usually will not show symptoms. The risk for two carrier parents to both pass the altered gene and have an affected child is 25% with each pregnancy. The risk to have a child who is a carrier like the parents is 50% with each pregnancy. The chance for a child to receive normal genes from both parents is 25%. The risk is the same for males and females.
Parents who are close relatives (consanguineous) have a higher chance than unrelated parents to both carry the same abnormal gene, which increases the risk to have children with a recessive genetic disorder.
Some clinicians theorize that the defect in development responsible for Hanhart syndrome may occur when there is an hemorrhagic lesion or an interruption of the necessary blood supply to the parts of the embryo that eventually develop into the arms, legs, hands, and feet (the limb buds); the tongue; the mouth and jaw area (Meckel’s cartilage); and, possibly in some cases, parts of the brain. It is projected that a clot has formed within a blood vessel (thrombus) or has traveled through the blood stream and become lodged in a vessel (embolus) is responsible for the interruption of blood flow. Such a clot may result from exposure of the embryo to certain drugs taken during pregnancy that decrease blood flow (hypoperfusion) through particular organs. Or a clot could result from the death of another embryo in the uterus that was originally formed from the same fertilized egg (discordant monozygotic twins).
Hanhart syndrome is a very rare developmental disorder that affects males and females in equal numbers. Fewer than 1 in 20,000 children are affected with this disorder. Approximately 30 cases of Hanhart syndrome were reported in the medical literature from 1932 to 1991.
Hanhart syndrome can be diagnosed in a newborn baby based upon a thorough clinical evaluation and characteristic physical findings.
The treatment of Hanhart syndrome requires the coordinated efforts of a team of specialists. Pediatricians, plastic and orthopedic surgeons, dental specialists, speech pathologists, physical therapists, and others must systematically and comprehensively plan the child’s treatment.
Infants with Hanhart syndrome may have feeding difficulties resulting from tongue, mouth, and/or jaw malformations and cranial nerve palsies that must be addressed immediately to ensure proper nutrition and growth. Abnormalities of the tongue, mouth, and jaw area may be treated through surgical correction, the use of artificial devices (prostheses) and/or physical therapy.
Children with Hanhart syndrome may benefit from speech therapy if speech is affected by tongue, mouth, and/or jaw malformations.
Depending on the severity of any limb abnormalities, children with Hanhart syndrome may have difficulty performing skills that require coordination of motion (motor skills), such as walking, writing, etc. Treatment may consist of surgery; the use of artificial replacements for parts of the arms, legs, hands, and/or feet that may be missing (limb prostheses); and/or physical therapy to help individuals enhance their motor skills.
Individuals with Hanhart syndrome may also benefit from special social support, special education, and vocational and occupational services. Other treatment is symptomatic and supportive, based upon the specifics of the affected individual’s case.
Genetic counseling is recommended for patients and their families.
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