Clinical Guidance
Schaaf-Yang Syndrome (SYS) is a rare, paternally derived neurodevelopmental disorder that shares multiple clinical features with the genetically related Prader-Willi syndrome. It usually manifests at birth with muscular hypotonia in all and distal joint contractures in a majority of affected individuals. To date, more than 250 individuals have been identified with a paternally derived pathogenic variant in MAGEL2 [, , , ]. The following description of the phenotypic features associated with this condition is based on these reports. Table 2. Select Features of Schaaf-Yang Syndrome
Feature | % of Personsw/Feature | Comment |
|---|
DD/ID | 100% | — |
Muscular hypotonia | 100% | — |
Infantile hypotonia | 95%-100% | — |
Feeding difficulties in infancy | 95%-100% | — |
Flexion contractures | 85% | — |
Autistic behavior | 75%-85% | — |
Dysmorphic features | 75%-85% | Incl pointed chin, frontal bossing, low-set ears |
Ocular anomalies | 75%-85% | Incl esotropia, myopia, strabismus |
Behavioral abnormalities | 70%-80% | Incl impulsivity, compulsivity, stubbornness, manipulative behavior, skin picking / automutilation |
Sleep apnea | 70%-80% | — |
Respiratory distress | 65%-75% | — |
Small hands | 65%-75% | Other hand anomalies: tapered fingers, clinodactyly, camptodactyly, brachydactyly, adducted thumbs |
Chronic constipation | 65%-75% | — |
Temperature instability | 60%-70% | — |
Short feet | 55%-65% | — |
fetal movement | 55%-65% | — |
GERD | 50%-60% | — |
Scoliosis | 50%-60% | — |
Short stature | 50%-60% | — |
Polyphagia/Obesity | 30%-40% | Onset in late childhood/adolescence. Frequency of this feature w/age. |
Seizures | 30%-40% | — |
Kyphosis | 25%-35% | — |
Hypogonadism | 15%-65% | 15%-25% of females 55%-65% of males, based on appearance of external genitalia Muscular hypotonia is, to a variable degree, present in almost all neonates with SYS, and can be severe in some instances. Reduced fetal movements may be reported prenatally. |
Source: GeneReviews — "Schaaf-Yang Syndrome"
