Aarskog syndrome is an extremely rare genetic disorder marked by stunted growth that may not become obvious until the child is about three years of age, broad facial abnormalities, musculoskeletal and genital anomalies, and mild intellectual disability.
Aarskog syndrome primarily affects males who exhibit a characteristic set of facial, skeletal, and genital abnormalities. In some cases, female carriers may develop a mild form of the disorder. Symptoms may vary from case to case. Males with Aarskog syndrome often have a rounded face with a broad forehead. Additional characteristic facial features include widely spaced eyes (ocular hypertelorism), drooping (ptosis) of the eyelids, downwardly slanting eyelid folds (palpebral fissures), a small nose with nostrils that are flared forward (anteverted nares), an underdeveloped upper jawbone (maxilliary hypoplasia), and a widow’s peak. Affected individuals may also have an abnormally long groove in the upper lip (philtrum) and a broad nasal bridge.
Affected individuals may also have a variety of abnormalities affecting the ears and teeth. Ear abnormalities include low-set ears and thickened, “fleshy” earlobes. Dental abnormalities include missing teeth at birth, delayed eruption of teeth, and underdevelopment of the hard outer covering of teeth (enamel hypoplasia).
Males with Aarskog syndrome also develop characteristic malformations of the skeletal system including disproportionate short stature; broad, short hands and feet; short, stubby fingers (brachydactyly) with permanent fixation of the fifth fingers in a bent position (clinodactyly); abnormally extendible finger joints; and wide flat feet with bulbous toes. In addition, affected individuals may have a sunken chest (pectus excavatum), protrusion of portions of the large intestine through an abnormal opening in the muscular lining of the abdominal cavity (inguinal hernia), and a prominent navel (umbilicus). Approximately 50 percent of individuals with Aarskog syndrome have spinal abnormalities such as incomplete closure of the bones of the spinal column (spina bifida occulta), fusion of the upper bones of the spinal column (cervical vertebrae), and underdevelopment of the “peg-like” projection of the second cervical vertebra (odontoid hypoplasia).
Males with Aarskog syndrome develop genital abnormalities including an abnormal fold of skin extending around the base of the penis (“shawl” scrotum) and/or failure of one or both of the testes to descend into the scrotum (cryptorchidism). In addition, the urinary opening (meatus) may be located on the underside of the penis (hypospadias) and the scrotum may appear clefted or divided (bifid scrotum).
Mild intellectual disability has occurred in some cases, but is not a consistent feature of the disorder. In some cases, affected children may exhibit hyperactivity, fail to gain weight and grow at the expected rate (failure to thrive), and develop chronic respiratory infections.
Additional symptoms may occur less frequently including congenital heart defects; abnormal side-to-side curvature of the spine (scoliosis); additional pairs of ribs; incomplete closure of the roof of the mouth (cleft palate) and/or a vertical groove in the upper lip (cleft lip); mild webbing of the fingers; and a short neck with or without webbing. Additional eye abnormalities may be present including crossed eyes (strabismus), farsightedness (hyperopia), and paralysis of certain eye muscles (ophthalmoplegia).
Clinical genetic investigations have demonstrated conclusively that Aarskog syndrome is transmitted as an X-linked recessive trait. Further studies indicate that the defective gene is located at Gene Map Locus Xp11.21. There is also some evidence that a second form of the disorder is distinguishable, and that this form is transmitted as a “sex-influenced autosomal dominant” trait. The occurrence of male dizygotic twins with an identical de novo mutation in FGD1 that resulted from germline mosaicism has recently been reported.
Chromosomes, which are present in the nucleus of human cells, carry the genetic information for each individual. Human body cells normally have 46 chromosomes. Pairs of human chromosomes are numbered from 1 through 22 and the sex chromosomes are designated X and Y. Males have one X and one Y chromosome and females have two X chromosomes. Each chromosome has a short arm designated “p” and a long arm designated “q”. Chromosomes are further sub-divided into many bands that are numbered. For example, “chromosome Xp11.21″ refers to band 11.21 on the short arm of the X chromosome. The numbered bands specify the location of the thousands of genes that are present on each chromosome.
Genetic diseases are determined by the combination of genes for a particular trait that are on the chromosomes received from the father and the mother.
All individuals carry a few abnormal genes. 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.
X-linked recessive genetic disorders are conditions caused by an abnormal gene on the X chromosome. Females have two X chromosomes but one of the X chromosomes is “turned off” and all of the genes on that chromosome are inactivated. Females who have a disease gene present on one of their X chromosomes are carriers for that disorder. Carrier females usually do not display symptoms of the disorder because it is usually the X chromosome with the abnormal gene that is turned off. Males have one X chromosome and if they inherit an X chromosome that contains a disease gene, they will develop the disease. Males with X-linked disorders pass the disease gene to all of their daughters, who will be carriers. Males cannot pass an X-linked gene to their sons because males always pass their Y chromosome instead of their X chromosome to male offspring. Female carriers of an X-linked disorder have a 25% chance with each pregnancy to have a carrier daughter like themselves, a 25% chance to have a non-carrier daughter, a 25% chance to have a son affected with the disease, and a 25% chance to have an unaffected son.
Aarskog syndrome is a rare disorder that primarily affects males. However, females who carry a single copy of the disease gene (heterozygotes) may exhibit some of the symptoms associated with the disorder. The disorder is estimated to occur in 1 in 1 million individuals in the general population. However, some mild cases often go unrecognized, making it difficult to determine the true frequency of Aarskog syndrome in the general population.
A diagnosis of Aarskog syndrome is made based upon a thorough clinical evaluation, a detailed patient history, and identification of characteristic findings. X-ray studies can identify distinctive characteristics of Aarskog syndrome and help to differentiate it from similar disorders.
The treatment of Aarskog syndrome is directed toward the specific symptoms that are apparent in each individual. Treatment may require the coordinated efforts of a team of specialists. Pediatricians, surgeons, cardiologists, dental specialists, speech pathologists, specialists who asses and treat hearing problems (audiologists), eye specialists, and other health care professionals may need to systematically and comprehensively plan an affected child's treatment.
Surgery may be necessary to treat specific congenital or structural malformations sometimes associated with Aarskog syndrome. Individuals with Aarskog syndrome should receive complete eye and dental evaluations. Genetic counseling may be of benefit for affected individuals and their families. Other treatment is symptomatic and supportive.
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Contact for additional information about Aarskog syndrome:
Marc B. Taub, OD
Chief of Vision Therapy and Rehabilitation Services
The Eye Center
Southern College of Optometry
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