Clinical Description
More than 340 individuals with classic Mowat-Wilson syndrome (MWS) have been reported in the medical literature [Ivanovski et al 2018]. The male-to-female ratio is roughly equivalent (183:161), although earlier reports suggested a male predominance [Ivanovski et al 2018].
Table 2.
Classic Mowat-Wilson Syndrome: Frequency of Select Clinical Features
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| Clinical Feature | % of Persons w/Feature | Comment |
|---|
| Epilepsy | 79% | May include electrical status epilepticus in sleep |
| Microcephaly 1 | 78% | |
| Hypospadias in males | 60% | |
| Congenital heart defects | 58% | Particularly anomalies of pulmonary arteries &/or valves |
| Short stature 2 | 46% | |
| Hirschsprung disease | 44% | |
| Cryptorchidism in males | 41% | |
| Constipation (w/o known Hirschsprung disease) | 29% | |
| Renal anomalies | 25% | |
| Structural eye anomalies | 10% | |
| Pyloric stenosis | 7% | |
| Pulmonary artery sling | 3% | |
| Cleft palate | 2% | |
- 1.
Head circumference ≥2 standard deviations below the mean for age and sex
- 2.
Length or height ≥2 standard deviations below the mean for age and sex
Craniofacial Features
Distinctive craniofacial features are a hallmark of classic MWS and, therefore, are one of the most specific findings (see Suggestive Findings and Genetically Related Disorders).
The facial phenotype evolves and becomes more pronounced with age (), such that the diagnosis is easier to make in older individuals:
The eyebrows may become heavier, broad, and horizontal.
The nasal tip lengthens and becomes more depressed and the nasal profile becomes more convex.
The columella becomes more pronounced, leading to the appearance of a short philtrum.
The face tends to elongate, and the jaw becomes more prominent.
However, the ear configuration does not change significantly with age, with the exception of the central depression, which is less obvious in adults.
Additional suggestive facial features include the following:
Telecanthus
Deeply set eyes
Wide nasal bridge with prominent and rounded nasal tip
Thick or everted vermilion of the lower lip
Increased posterior angulation of the ears
Other rare craniofacial findings include the following:
Palatal anomalies (bifid uvula, submucous cleft palate, and cleft of the hard palate)
Unicoronal craniosynostosis
Growth
Classic MWS growth charts have been published (see Management) [Ivanovski et al 2020].
Birth weight and length are typically in the normal range.
Microcephaly (head circumference ≥2 standard deviations [SD] below the mean for age and sex) is most often acquired but can be present at birth.
Short stature (defined as length or height ≥2 SD below the mean for age and sex) typically develops over time, with a mean adult height of 165.1 cm in males and 150.5 cm in females [Ivanovski et al 2018].
Body habitus is frequently lean and slender, with about 30% of affected individuals having a weight below the third centile for age and sex.
Eyes
Strabismus is the most common finding, present in more than half of affected individuals. Astigmatism and myopia are also common findings. Nystagmus has been described in some individuals, particularly in infancy; it often resolves with age.
About 10% of affected individuals have structural eye anomalies or optic nerve findings, including the following [Ivanovski et al 2018, Tronina et al 2023, Wójcik-Niklewska & Filipek 2024]:
Microphthalmia
Axenfeld anomaly / posterior embryotoxon; at least one affected individual had acquired and progressive anterior iris synechiae [
Hernández-Marrero et al 2024].
Ptosis
Congenital or acquired cataract
Retinal aplasia or retinal pigment epithelium atrophy
Optic nerve hypoplasia or atrophy
Abnormalities of the optic nerve disc
Ears
Recurrent otitis media, which can cause conductive hearing loss, has been described in about one third of affected individuals. Due to a high pain threshold seen in many affected individuals (see Psychosocial and Cognitive Development), unexplained fever should prompt the clinician to consider otitis media as a potential cause.
Sensorineural hearing loss has only rarely been described [Ivanovski et al 2018].
Dental Findings
Widely spaced teeth, malpositioned teeth, delayed tooth eruption, malformed teeth, dental crowding, gingival hypertrophy, and/or bruxism have been described [Ivanovski et al 2018].
Cardiovascular Defects
Structural heart defects are present in almost 60% of individuals with classic MWS, with multiple different types of congenital heart defects reported. The most common findings are septal defects and patent ductus arteriosus. More complex congenital heart defects, however, have been reported and include the following [Ivanovski et al 2018]:
Gastrointestinal (GI) Issues
Classic MWS was initially described as a syndromic form of Hirschsprung disease (HSCR); however, only 44% of individuals with classic MWS have biopsy-proven HSCR.
Chronic constipation has been described in about 30% of persons with classic MWS without documented HSCR [Ivanovski et al 2018]. It is unclear whether chronic constipation results from ultrashort HSCR or the presence of some other partial defect in ganglion function. Additionally, submucosal supernumerary smooth muscle coat has been identified more commonly in people with classic MWS than in the general population [Suchi et al 2020]. However, the clinical significance of this finding in individuals with classic MWS is unclear.
Chronic constipation typically becomes more common with age, likely due to a combination of factors, including insufficient liquid intake, low-fiber diet, and less vigilance in tracking stool output and consistency by caregivers [Niemczyk et al 2017].
Surgical outcomes for HSCR in individuals with classic MWS are generally worse than surgical outcomes for those with nonsyndromic HSCR; complications may include prolonged need for total parenteral nutrition and/or recurrent enterocolitis [Smigiel et al 2010]. The increased complication rate may be due in part to a generalized gut motility disorder, which can also affect the upper GI tract.
Other GI findings include the following:
Kidney Anomalies
Kidney anomalies are present in about one quarter of affected individuals and most commonly consist of vesicoureteral reflux and hydronephrosis. Other, less common findings may include duplex kidney, pelvic kidney, and multicystic dysplastic kidney.
Genital Anomalies
About 60% of males have hypospadias, while about 40% have cryptorchidism. Less common findings in males may include bifid scrotum, penile chordee or "webbed penis," micropenis, macro-orchidism, or hydrocele.
Septum of the vagina has been described rarely in females.
Pubertal Development
Very little has been written regarding pubertal development in classic MWS. One female age 17 years underwent menarche at age 15 years but had inconsistent menstruation. One male underwent normal pubertal development. One male had mildly delayed pubertal development [Adam et al 2006]. In the experience of the authors, most affected adults undergo typical pubertal development.
Skeletal Findings
A variety of skeletal manifestations have been described in individuals with classic MWS. Among the most common skeletal manifestations are long, slender, tapered fingers. In later childhood and adulthood, the interphalangeal joints may become prominent. Calcaneovalgus deformity of the feet is also common.
Findings seen in up to 50% of affected individuals include the following:
Pectus anomalies (excavatum or carinatum)
Scoliosis
Adducted thumbs
Ulnar deviation of the hands
Mild contractures of the joints and/or camptodactyly
Genu valgus
Pes planus
Long toes with or without long and/or broad halluces
Hallux valgus
Delayed bone age
Syndactyly
Rarely, individuals with MWS have sustained frequent fractures that responded to bisphosphonate therapy [MP Adam, personal observation]. This is most likely a secondary finding resulting from decreased weight-bearing activity.
Neurologic Findings
Neurologic findings are very common in individuals with classic MWS.
Tone. A majority of individuals younger than age one year have hypotonia. Hypotonia may transition to spasticity in adolescence or adulthood. Spasticity can lead to joint contractures and mobility issues, which in turn can cause decreased weight-bearing activity and an increased risk of low bone mineral density with propensity to fractures (see Skeletal Findings).
Epilepsy is one of the most common neurologic issues in individuals with classic MWS, present in almost 80% of affected individuals [Ivanovski et al 2018].
Mean age of onset is around three years, although first presentation of seizure as early as age one month and as late as 11 years has been reported [
Ivanovski et al 2018].
Multiple seizure types have been described; types most frequently seen are focal and atypical absence seizures. For many individuals, the first seizure is a focal seizure associated with fever.
Up to 25% of affected individuals have seizures that are difficult to control (more so in childhood than in adolescence or adulthood) or refractory to conventional anti-seizure medications.
Vagal nerve stimulator implantation resulted in reduction of seizure frequency in at least two affected individuals.
In at least one other individual, anti-seizure medications were discontinued in adulthood with no recurrence of seizures.
EEG abnormalities may be age dependent. EEGs performed at seizure presentation frequently demonstrate only mild slowing of background activity or are interpreted as normal. Repeat studies may show irregular diffuse frontally dominant and occasionally asymmetric spike and wave discharges. During slow-wave sleep the abnormalities are accentuated, resulting in continuous or near-continuous spike and wave activity.
Electrical status epilepticus during sleep (ESES) has been described in multiple individuals who have undergone overnight EEG studies [
Bonanni et al 2017]. In one study of 36 individuals with MWS and epilepsy, 14/36 (39%) had ESES [
Ricci et al 2021].
The presence of ESES can negatively affect behavior as well as motor and cognitive function.
Evaluation for ESES should be considered in any affected individual who has experienced regression in cognitive function or motor skills, such as the development of ataxia or dyspraxia.
Seizure activity does not appear to correlate with structural brain anomalies.
Central Nervous System
Central nervous system anomalies are present in approximately half of individuals who have been imaged. The most common findings are abnormalities of the corpus callosum (i.e., hypoplasia, partial or complete agenesis). A variety of other anomalies, including the following [Garavelli et al 2017], have been described:
Ventricular enlargement (lateral ventricle or ventricular temporal horn)
Abnormalities of the hippocampus
Cortical malformations (polymicrogyria, periventricular heterotopia, focal cortical dysplasia)
Reduction of white matter thickness
Localized signal alterations of the white matter
Posterior fossa malformations (absent or small cerebellar vermis, macrocerebellum)
Large basal ganglia
Psychosocial and Cognitive Development
All individuals with classic MWS have moderate-to-severe intellectual disability, although the results of formal IQ testing have not been reported in most studies. Individuals with pathogenic missense variants may have milder features, including milder cognitive disabilities (see Genotype-Phenotype Correlations and Genetically Related Disorders).
Speech. The vast majority of affected individuals older than age one year have severely impaired verbal language skills, with either absent or severely restricted speech. Rare individuals with classic MWS have some speech capabilities, including the ability to use short sentences [MP Adam, personal observation].
Gross motor milestones are generally delayed.
Mean age of walking is between ages three and four years (range: 23 months to 8 years); some individuals do not achieve ambulation.
The gait is typically wide based with the arms held up and flexed at the elbow.
Fine motor skills are also delayed. Most affected individuals require lifelong help with dressing and other activities of daily living.
Toileting. Most individuals with MWS remain incontinent of stool and urine throughout life [Niemczyk et al 2017].
Behavior. Many individuals have been described as having a happy demeanor with frequent laughter. In comparison to individuals who have moderate-to-severe cognitive impairment due to other causes, individuals with classic MWS display similarly high levels of behavioral or emotional findings, including disruptive/antisocial behavior, self-absorbed behavior, and anxiety. Other associated behaviors seen in more than half of affected individuals include:
Sleep. About half of individuals with classic MWS have some degree of sleep disturbance, which may include frequent nighttime waking and early morning wakening. Clinicians should consider screening individuals with classic MWS for features of sleep disturbance, with referral to a sleep disorders clinic if there are clinical concerns.
Immunologic Findings
Asplenia has been reported in several individuals with classic MWS; one individual had a severe course that included purpura fulminans [Nevarez Flores et al 2019].
Current data does not suggest that there is a common immunodeficiency phenotype in people with classic MWS. In individuals studied, there is a skewing of T cells away from CD8 differentiation, but this had only a slight effect on immune system function [Frith et al 2021].
However, several affected individuals have required treatment with intravenous immunoglobulin (IVIG) for antibody deficiency leading to recurrent infections [MP Adam, personal observation].
Anesthesia Risk
The most common management issue is the rare finding of a difficult airway at the time of intubation [Deshmukh et al 2016, Packiasabapathy et al 2016]. Other reported anesthetic challenges have included longer time to wean respiratory support, presence of anemia, and concomitant lower respiratory tract infection [Spunton et al 2018]. However, there does not appear to be a true increased risk of adverse outcome from anesthesia due to this condition itself.
Additional Findings
The following findings have each been described in one affected individual. It is unclear whether these are rare features of MWS or if they represent unrelated co-occurrences.
Prognosis
It is unknown if life span in individuals with classic MWS is abnormal. One reported individual is alive at age 60 years [MP Adam, personal observation], demonstrating that survival into adulthood is possible. Since many adults with disabilities have not undergone advanced genetic testing, it is likely that adults with this condition are underrecognized and underreported.