Usually associated with diaphragmatic hernia,

pulmonary hypoplasia,

imperforate anus,

micropenis,

bilateral cryptorchidism,

cerebral ventricular dilation,

camptodactyly,

agenesis of sacrum,

low-set ear.

- Fryns et al. (1979) reported 2 stillborn sisters with a multiple congenital anomaly syndrome characterized by coarse facies with cloudy corneae, diaphragmatic defects, absence of lung lobulation, and distal limb deformities. A sporadic case was reported by Goddeeris et al. (1980). Fitch (1988) claimed that she and her colleagues were the first to describe this disorder. In 1978 they reported a single infant, born of second-cousin parents, who had absent left hemidiaphragm, hydrocephalus, arhinencephaly, and cardiovascular anomalies.

- Lubinsky et al. (1983) reported a brother and sister with Fryns syndrome who both died in the neonatal period. Facial anomalies included broad nasal bridge, microretrognathia, abnormal helices, and cleft palate. Other features included distal digital hypoplasia, lung hypoplasia, and urogenital abnormalities, including shawl scrotum, uterus bicornis, and renal cysts. They were discordant for diaphragmatic hernia, cleft lip, and Dandy–Walker anomaly.

- Meinecke and Fryns (1985) reported an affected child; consanguinity of the parents supported recessive inheritance. They noted that a diaphragmatic defect had been described in 4 of the 5 reported cases and lung hypoplasia in all. Young et al. (1986) reported a sixth case. The male infant survived for 12 days. These authors listed corneal clouding, camptodactyly with hypoplastic nails, and abnormalities of the diaphragm as cardinal features.

- Samueloff et al. (1987) described a family in which all 4 children had Fryns syndrome and neonatal mortality. Features included hypoplastic lungs, cleft palate, retrognathia, micrognathism, small thorax, diaphragmatic hernia, distal limb hypoplasia, and early onset of polyhydramnios with premature delivery. Schwyzer et al. (1987) described an affected infant whose parents were second cousins.

- Moerman et al. (1988) described infant brother and sister with the syndrome of diaphragmatic hernia, abnormal face, and distal limb anomalies. Both died shortly after birth with severe respiratory distress. Ultrasonography demonstrated fetal hydrops, diaphragmatic hernia, and striking dilatation of the cerebral ventricles in both infants. Post-mortem examination showed Dandy–Walker malformation, ventricular septal defect, and renal cystic dysplasia.

- Cunniff et al. (1990) described affected brothers and 3 other cases, bringing the total reported cases of Fryns syndrome to 25. One of the affected brothers was still alive at the age of 24 months. Bilateral diaphragmatic hernias had been repaired on the first day of life. He required extracorporeal membrane oxygenation therapy for 5 days and oscillatory therapy for 3 months. Ventriculoperitoneal shunt was required because of slowly progressive hydrocephalus. Scoliosis was associated with extranumerary vertebral bodies and 13 ribs. Because of delayed gastric emptying, a gastrostomy tube was inserted. In addition, because of persistent chylothorax, he underwent decortication of the right lung and oversewing of the thoracic duct.

- Kershisnik et al. (1991) suggested that osteochondrodysplasia is a feature of Fryns syndrome.

- Willems et al. (1991) suggested that a diaphragmatic hernia is not a necessary feature of Fryns syndrome. They described a child with all the usual features except for diaphragmatic hernia; the diaphragm was reduced to a fibrous web with little muscular component. Bartsch et al. (1995) presented 2 unrelated cases with a typical picture of Fryns syndrome but without diaphragmatic hernia. One of these patients was alive at the age of 14 months, but was severely retarded. Bamforth et al. (1987) and Hanssen et al. (1992) also described patients with this syndrome who survived the neonatal period. In the report of Hanssen et al. (1992), 2 older sibs had died in utero. The reports suggested that survival beyond the neonatal period is possible when the diaphragmatic defect and lung hypoplasia are not present. However, mental retardation has been present in all surviving patients.

- Vargas et al. (2000) reported a pair of monozygotic twins with Fryns syndrome discordant for severity of diaphragmatic defect. Both twins had macrocephaly, coarse facial appearance, hypoplasia of distal phalanges, and an extra pair of ribs. Twin A lacked an apparent diaphragmatic defect, and at 1 year of age had mild developmental delay. Twin B had a left congenital diaphragmatic hernia and died neonatally. The authors suggested that absence of diaphragmatic defect in Fryns syndrome may represent a subpopulation of more mildly affected patients.

- Aymé, "et al." (1989) described 8 cases of Fryns syndrome in France. The most frequent anomalies were diaphragmatic defects, lung hypoplasia, cleft lip and palate, cardiac defects, including septal defects and aortic arch anomalies, renal cysts, urinary tract malformations, and distal limb hypoplasia. Most patients also had hypoplastic external genitalia and anomalies of internal genitalia, including bifid or hypoplastic uterus or immature testes. The digestive tract was also often abnormal; duodenal atresia, pyloric hyperplasia, malrotation and common mesentery were present in about half of the patients. When the brain was examined, more than half were found to have Dandy–Walker anomaly and/or agenesis of the corpus callosum. A few patients demonstrated cloudy cornea. Histologically, 2 of 3 patients showed retinal dysplasia with rosettes and gliosis of the retina, thickness of the posterior capsule of the lens, and irregularities of Bowman membrane.

- Alessandri et al. (2005) reported a newborn from the Comores Islands with clinical features of Fryns syndrome without diaphragmatic hernia. They noted that diaphragmatic hernia is found in more than 80% of cases and that at least 13 other cases had been reported with an intact diaphragm.

- In a postneonatal survivor of Fryns syndrome, Riela et al. (1995) described myoclonus appearing shortly after birth, which was well controlled on valproate. Progressive cerebral and brainstem atrophy was noted on serial MRIs made at 3 months and after 6 months of age.

- Van Hove et al. (1995) described a boy with Fryns syndrome who survived to age 3 years and reviewed the outcome of other reported survivors (approximately 14% of reported cases). Survivors tended to have less frequent diaphragmatic hernia, milder lung hypoplasia, absence of complex cardiac malformation, and severe neurologic impairment. Their patient had malformations of gyration and sulcation, particularly around the central sulcus, and hypoplastic optic tracts beyond the optic chiasm associated with profound mental retardation.

- Fryns and Moerman (1998) reported a second-trimester male fetus with Fryns syndrome and midline scalp defects. The authors stated that the finding of a scalp defect in Fryns syndrome confirms that it is a true malformation syndrome with major involvement of the midline structures.

- Ramsing et al. (2000) described 2 sibships with 4 fetuses and 1 preterm baby of 31 weeks' gestation affected by a multiple congenital disorder suggestive of Fryns syndrome. In addition to the diaphragmatic defects and distal limb anomalies, they presented with fetal hydrops, cystic hygroma, and multiple pterygias. Two affected fetuses in 1 family showed severe craniofacial abnormalities with bilateral cleft lip and palate and cardiovascular malformation.

- Arnold et al. (2003) reported a male fetus with Fryns syndrome and additional abnormalities, in particular, multiple midline developmental defects including gastroschisis, central nervous system defects with left arrhinencephaly and cerebellar hypoplasia, midline cleft of the upper lip, alveolar ridge, and maxillary bone, and cleft nose with bilateral choanal atresia.

- Pierson et al. (2004) reviewed 77 reported patients with Fryns syndrome and summarized the abnormal eye findings identified in 12 of them. They also described 3 new patients with Fryns syndrome, 1 of whom demonstrated unilateral microphthalmia and cloudy cornea.

- Slavotinek et al. (2005) noted that Fryns syndrome may be the most common autosomal recessive syndrome in which congenital diaphragmatic hernia (see DIH2, 222400) is a cardinal feature. The autosomal recessive inheritance in Fryns syndrome contrasts with the sporadic inheritance for most patients with DIH.

Fryns syndrome is an autosomal recessive multiple congenital anomaly syndrome that is usually lethal in the neonatal period. Fryns (1987) reviewed the syndrome.

The following features are observed with VACTERL association:

- V - Vertebral anomalies

- A - Anorectal malformations

- C - Cardiovascular anomalies

- T - Tracheoesophageal fistula

- E - Esophageal atresia

- R - Renal (Kidney) and/or radial anomalies

- L - Limb defects

Although it was not conclusive whether VACTERL should be defined by at least two or three component defects, it is typically defined by the presence of at least three of the above congenital malformations.

Renal (kidney) defects are seen in approximately 50 percent of patients with VACTERL association. In addition, up to 35 percent of patients with VACTERL association have a single umbilical artery (there are usually two arteries and one vein) which is often associated with additional kidney or urologic problems. Renal abnormalities in VACTERL association can be severe, with incomplete formation of one or both kidneys or urologic abnormalities such as obstruction of outflow of urine from the kidneys or severe reflux (backflow) of urine into the kidneys from the bladder. These problems can cause kidney failure early in life and may require kidney transplant. Many of these problems can be corrected surgically before any damage can occur.

Heart abnormalities are present in 25–35% of people with distal 18q-. The majority of these defects are septal. Congenital orthopedic anomalies are also relatively common, particularly rocker-bottom feet or clubfoot. Cleft lip and palate are relatively common in people with distal 18q-. Kidney abnormalities have also been reported and include horseshoe kidney, hydronephrosis, polycystic kidney, and absent kidney. Boys with distal 18q- may have genital anomalies, the most frequent being cryptorchidism and hypospadias.

People with Aarskog-Scott syndrome often have distinctive facial features, such as widely spaced eyes (hypertelorism), a small nose, a long area between the nose and mouth (philtrum), and a widow's peak hairline. They frequently have mild to moderate short stature during childhood, but their growth usually catches up with that of their peers during puberty. Hand abnormalities are common in this syndrome and include short fingers (brachydactyly), curved pinky fingers (fifth finger clinodactyly), webbing of the skin between some fingers (cutaneous syndactyly), and a single crease across the palm. Other abnormalities in people with Aarskog-Scott syndrome include heart defects and a split in the upper lip (cleft lip) with or without an opening in the roof of the mouth (cleft palate).

Most males with Aarskog-Scott syndrome have a shawl scrotum, in which the scrotum surrounds the penis instead of hanging below. Less often, they have undescended testes (cryptorchidism) or a soft out-pouching around the belly-button (umbilical hernia) or in the lower abdomen (inguinal hernia).

The intellectual development of people with Aarskog-Scott syndrome varies widely. Some may have mild learning and behavior problems, while others have normal intelligence. In rare cases, severe intellectual disability has been reported.

Hemangiomas associated with PHACE Syndrome are usually small or not visible at birth, but are easier to see during the first days to weeks of life. They can grow rapidly. Hemangiomas linked with PHACE Syndrome tend to cover a large area of the face, head or neck, either as one lesion or as many single lesions.

Hypotonia is a common finding. Around 10% of people with distal 18q- have seizures.

It is characterized by developmental defects including cryptophthalmos (where the eyelids fail to separate in each eye), and malformations in the genitals (such as micropenis, cryptorchidism or clitoromegaly). Congenital malformations of the nose, ears, larynx and renal system, as well as mental retardation, manifest occasionally. Syndactyly (fused fingers or toes) has also been noted.

Impossible Syndrome, or Chondrodysplasia situs inversus imperforate anus polydactyly, is a complex combination of human congenital malformations (birth defects).

The malformations include chondrodysplasia (improper growth of bone and cartilage), situs inversus totalis (chest and abdominal organs all a mirror image of normal), cleft larynx and epiglottis, hexadactyly (six digits) on hands and feet, diaphragmatic hernia, pancreatic abnormalities, kidney abnormal on one side and absent on the other side, micropenis and ambiguous genitalia, and imperforate anus.

Only one case of Impossible Syndrome has been reported; the infant was premature and stillborn.

As it grows, the hemangioma can break down skin, distort facial features or get in the way of other vital functions, such as breathing, vision, and hearing. Other complications will depend on what other structures are involved. These could include developmental delay, seizures, headaches, and abnormal muscle tone if the brain is involved.

The Pai Syndrome is a rare subtype of frontonasal dysplasia. It is a triad of developmental defects of the face, comprising midline cleft of the upper lip, nasal and facial skin polyps and central nervous system lipomas. When all the cases are compared, a difference in severity of the midline cleft of the upper lip can be seen. The mild form presents with just a gap between the upper teeth. The severe group presents with a complete cleft of the upper lip and alveolar ridge.

Nervous system lipomas are rare congenital benign tumors of the central nervous system, mostly located in the medial line and especially in the corpus callosum. Generally, patients with these lipomas present with strokes. However, patients with the Pai syndrome don’t. That is why it is suggested that isolated nervous system lipomas have a different embryological origin than the lipomas present in the Pai syndrome. The treatment of CNS lipomas mainly consists of observation and follow up.

Skin lipomas occur relatively often in the normal population. However, facial and nasal lipomas are rare, especially in childhood. However, the Pai syndrome often present with facial and nasal polyps. These skin lipomas are benign, and are therefore more a cosmetic problem than a functional problem.

The skin lipomas can develop on different parts of the face. The most common place is the nose. Other common places are the forehead, the conjunctivae and the frenulum linguae. The amount of skin lipomas is not related to the severity of the midline clefting.

Patients with the Pai syndrome have a normal neuropsychological development.

Until today there is no known cause for the Pai syndrome.

The large variety in phenotypes make the Pai syndrome difficult to diagnose. Thus the incidence of Pai syndrome seems to be underestimated.

Two key features of AOS are aplasia cutis congenita with or without underlying bony defects and terminal transverse limb defects. Cutis aplasia congenita is defined as missing skin over any area of the body at birth; in AOS skin aplasia occurs at the vertex of the skull. The size of the lesion is variable and may range from solitary round hairless patches to complete exposure of the cranial contents. There are also varying degrees of terminal limb defects (for example, shortened digits) of the upper extremities, lower extremities, or both. Individuals with AOS may have mild growth deficiency, with height in the low-normal percentiles. The skin is frequently observed to have a mottled appearance (cutis marmorata telangiectatica congenita). Other congenital anomalies, including cardiovascular malformations, cleft lip and/or palate, abnormal renal system, and neurologic disorders manifesting as seizure disorders and developmental delay are sometimes observed. Variable defects in blood vessels have been described, including hypoplastic aortic arch, middle cerebral artery, pulmonary arteries. Other vascular abnormalities described in AOS include absent portal vein, portal sclerosis, arteriovenous malformations, abnormal umbilical veins, and dilated renal veins.

Malpuech syndrome is congenital, being apparent at birth. It is characterized by a feature known as facial clefting. Observed and noted in the initial description of the syndrome as a cleft lip and palate, facial clefting is identified by clefts in the bones, muscles and tissues of the face, including the lips and palate. The forms of cleft lip and palate typically seen with Malpuech syndrome are midline (down the middle of the lip and palate) or bilateral (affecting both sides of the mouth and palate). Facial clefting generally encompasses a wide range of severity, ranging from minor anomalies such as a (split) uvula, to a cleft lip and palate, to major developmental and structural defects of the facial bones and soft tissues. Clefting of the lip and palate occurs during embryogenesis. Additional facial and ortho-dental anomalies that have been described with the syndrome include: hypertelorism (unusually wide-set eyes, sometimes reported as telecanthus), narrow palpebral fissures (the separation between the upper and lower eyelids) and ptosis (drooping) of the eyelids, frontal bossing (prominent eyebrow ridge) with synophris, highly arched eyebrows, wide nasal root and a flattened nasal tip, malar hypoplasia (underdeveloped upper cheek bone), micrognathia (an undersized lower jaw), and prominent incisors. Auditory anomalies include an enlarged ear ridge, and hearing impairment associated with congenital otitis media (or "glue ear", inflammation of the middle ear) and sensorineural hearing loss.

Another feature identified with Malpuech syndrome is a caudal appendage. A caudal appendage is a congenital outgrowth stemming from the coccyx (tailbone). Present in many non-human animal species as a typical tail, this feature when seen in an infant has been described as a "human tail". This was observed by Guion-Almeida (1995) in three individuals from Brazil. The appendage on X-rays variously appeared as a prominent protrusion of the coccyx. On a physical examination, the appendage resembles a nodule-like stub of an animal tail.

Deficiencies such as mental retardation, learning disability, growth retardation and developmental delay are common. Psychiatric manifestations that have been reported with the syndrome include psychotic behavior, obsessive–compulsive disorder, loss of inhibition, hyperactivity, aggression, fear of physical contact, and compulsive actions like echolalia (repeating the words spoken by another person). Neuromuscular tics have also been noted.

Urogenital abnormalities, or those affecting the urinary and reproductive systems, are common with the syndrome. Malpuech et al. (1983) and Kerstjens-Frederikse et al. (2005) reported variously in affected males a micropenis, hypospadias (a congenital mislocation of the urinary meatus), cryptorchidism ( or undescended testes), bifid (split) and underdeveloped scrotum, and an obstructive urethral valve. An affected boy was also reported by Reardon et al. (2001) with left renal agenesis, an enlarged and downwardly displaced right kidney, cryptorchidism and a shawl scrotum. Other malformations that have been noted with the syndrome are omphalocele and an umbilical hernia.

Congenital abnormalities of the heart have also been observed with Malpuech syndrome. From a healthy Japanese couple, Chinen and Naritomi (1995) described the sixth child who had features consistent with the disorder. This two-month-old male infant was also affected by cardiac anomalies including patent ductus arteriosus (PDA) and ventricular septal defect. The opening in the ductus arteriosus associated with PDA had been surgically repaired in the infant at 38 days of age. A number of minor skeletal aberrations were also reported in the infant, including wormian bones at the lambdoid sutures.

This classification is based on the morphologic characteristics of FND, that describes a variety of phenotypes

Both of these classifications are further described in table 1. This table originates from the article ‘Acromelic frontonasal dysplasia: further delineation of a subtype with brain malformations and polydactyly (Toriello syndrome)', Verloes et al.

Characteristics include varying degrees of developmental disability, epilepsy, hypotonia, and both hypopigmentation and hyperpigmentation. Patients also exhibit a distinctive facial structure, characterized by high foreheads, sparse hair on the temple, a wide space between the eyes, epicanthal folds, and a flat nose. Vision and hearing impairments may occur. Patients may also exhibit congenital heart defects, gastroesophageal reflux, cataracts, and supernumerary nipples. Diaphragm problems seen in newborns can lead to death shortly after birth.

- As patients pass into adolescence, the syndrome is characterized by a coarse and flat face, macroglossia, prognathism, inverted lower lip, and psychomotor retardation with muscular hypertonia and contractures.

The diagnosis of constriction ring syndrome can be confirmed with an ultrasonography. The clinical manifestations can be extremely variable. It could be a single or multiple manifestation. This can be confirmed at the end of the first trimester or at the beginning of the second trimester. But not every patient will be diagnosed at that moment, most will get this diagnosis at birth.

The differential diagnosis includes;

- Symbrachydactyly

- Chorionic villus sampling

- Congenital amputations

- Hypoplasias of hand, digit, thumb

- Adams-Oliver syndrome

- ADAM complex

ADAM Complex; CRS is sometimes mislabeled as ADAM complex. ADAM is an abbreviation for Amniotic Deformity, Adhesions Mutilations. CRS is the malformation due to a constriction ring around mostly a limb. ADAM-complex is the association of limb defects (caused by constriction rings) and certain craniofacial clefts

“Adams-Oliver syndrome is often mislabeled as CRS and consists of cutis aplasia of the scalp in which a longitudinal defect can vary in size and can often be associated with full-thickness skullcap loss. The distal digital or toe hypoplasia-aplasia is often confused with CRS. Constriction rings with or without edema are not present. The digital or toe hypoplasia-aplasia usually contains diminutive nails or nail folds”.

SHORT is an acronym for short stature, hyperextensibility of joints and/or inguinal hernia, ocular depression, rieger anomaly and teething delay.

Other characteristics common in SHORT syndrome are a triangular face, small chin with a dimple, a loss of fat under the skin (lipodystrophy), abnormal position of the ears, hearing loss and delayed speech.

Limb body wall complex (LBWC) is a rare fetal malformation of unknown origins.

Traditionally diagnosis has been based on the Van Allen et al., criteria, i.e. the presence of two out of three of the following anomalies:

1. Exencephaly or encephalocele with facial clefts

2. Thoraco and or abdominoschisis and

3. Limb defects.

LBWC occurs in approximately 0.32 in 100,000 births.

At this time, there is no known cause of Limb Body Wall Complex. However, there have been tentative links made between a diagnosis of LBWC and cocaine use. In addition, current research has shown that there may be a genetic cause for a small limited number of LBWC cases.

Limb Body Wall Complex is a lethal birth defect. There are only anecdotal stories of survivors.

Aarskog–Scott syndrome is a rare disease inherited as X-linked and characterized by short stature, facial abnormalities, skeletal and genital anomalies. This condition mainly affects males, although females may have mild features of the syndrome.

The Aarskog–Scott syndrome (AAS) is also known as the Aarskog syndrome, faciodigitogenital syndrome, shawl scrotum syndrome and faciogenital dysplasia.

Very frequent signs

- Abnormal gastrointestinal tract

- Absent pectoral muscles

- Brachydactyly (Short fingers)

- Dextrocardia

- Diaphragmatic hernia/defect

- Humerus absent/abnormal

- Liver/biliary tract anomalies

- Maternal diabetes

- Oligodactyly/missing fingers

- Radius absent/abnormal

- Rhizomelic micromelia (relatively shorter proximal segment of the limbs compared to the middle and the distal segments)

- Sparsity or abnormality of axillary hair on affected side

- Syndactyly of fingers (webbing)

- Ulna absent/abnormal

- Upper limb asymmetry

- Abnormal rib

- Simian crease on affected side

Frequent signs

- Hypoplastic/absent nipples

- Scapula anomaly

Occasional signs

- Agenesis/hypoplasia of kidneys

- Encephalocele/exencephaly

- Abnormal morphology of hypothalamic-hypophyseal axis

- Abnormal function of hypothalamic-hypophyseal axis

- Microcephaly

- Preaxial polydactyly

- Ureteric anomalies (reflux/duplex system)

- Vertebral segmentation anomaly

Beckwith–Wiedemann syndrome (; abbreviated BWS) is an overgrowth disorder usually present at birth, characterized by an increased risk of childhood cancer and certain congenital features.

Common features used to define BWS are:

- macroglossia (large tongue),

- macrosomia (above average birth weight and length),

- microcephaly

- midline abdominal wall defects (omphalocele/exomphalos, umbilical hernia, diastasis recti),

- ear creases or ear pits,

- neonatal hypoglycemia (low blood sugar after birth).

- Hepatoblastoma

Most children with BWS do not have all of these five features. In addition, some children with BWS have other findings including: nevus flammeus, prominent occiput, midface hypoplasia, hemihypertrophy, genitourinary anomalies (enlarged kidneys), cardiac anomalies, musculoskeletal abnormalities, and hearing loss. Also, some premature newborns with BWS do not have macroglossia until closer to their anticipated delivery date.

Given the variation among individuals with BWS and the lack of a simple diagnostic test, identifying BWS can be difficult. In an attempt to standardize the classification of BWS, DeBaun et al. have defined a child as having BWS if the child has been diagnosed by a physician as having BWS and if the child has at least two of the five common features associated with BWS (macroglossia, macrosomia, midline abdominal wall defects, ear creases/ear pits, neonatal hypoglycemia). Another definition presented by Elliot et al. includes the presence of either three major features (anterior abdominal wall defect, macroglossia, or prepostnatal overgrowth) or two major plus three minor findings (ear pits, nevus flammeus, neonatal hypoglycemia, nephromegaly, or hemihyperplasia).

While most children with BWS do not develop cancer, children with BWS do have a significantly increased risk of cancer. Children with BWS are most at risk during early childhood and should receive cancer screening during this time.

In general, children with BWS do very well and grow up to become adults of normal size and intelligence, usually without the syndromic features of their childhood.

Malpuech facial clefting syndrome, also called Malpuech syndrome or Gypsy type facial clefting syndrome, is a rare congenital syndrome. It is characterized by facial clefting (any type of cleft in the bones and tissues of the face, including a cleft lip and palate), a appendage (a "human tail"), growth deficiency, intellectual and developmental disability, and abnormalities of the renal system (kidneys) and the male genitalia. Abnormalities of the heart, and other skeletal malformations may also be present. The syndrome was initially described by Guilliaume Malpuech and associates in 1983. It is thought to be genetically related to Juberg-Hayward syndrome. Malpuech syndrome has also been considered as part of a spectrum of congenital genetic disorders associated with similar facial, urogenital and skeletal anomalies. Termed "3MC syndrome", this proposed spectrum includes Malpuech, Michels and Mingarelli-Carnevale (OSA) syndromes. Mutations in the "COLLEC11" and "MASP1" genes are believed to be a cause of these syndromes. The incidence of Malpuech syndrome is unknown. The pattern of inheritance is autosomal recessive, which means a defective (mutated) gene associated with the syndrome is located on an autosome, and the syndrome occurs when two copies of this defective gene are inherited.