Otopalatodigital Syndrome Type 2

A severe form of otopalatodigital syndrome spectrum disorder, and is characterized by dysmorphic facies, severe skeletal dysplasia affecting the axial and appendicular skeleton, extraskeletal anomalies (including malformations of the brain, heart, genitourinary system, and intestine) and poor survival.

Epidemiology

To date, more than 40 cases of Otopalatodigital syndrome type 2 (OPD2) have been described in the literature.

Clinical description

OPD2 is a congenital disorder. Intrauterine growth is usually normal and affected infants have large anterior fontanels, and facial dysmorphism including broad forehead and lateral fullness of the supraorbital ridge, hypertelorism, downslanting palpebral fissures, stubby nose with a flat root, midfacial hypoplasia, microstomia (with typical down turned bow of the upper lip), micrognathia, Pierre Robin sequence, posterior cleft palate (submucosal cleft palate or cleft velum), glossoptosis, malformed and/or apparently low-set ears. Additional features include skeletal anomalies: pectus deformity, short limbs, campomelia, fibular agenesis, flexion contractures of elbows, knees, rocker bottom or equinovarus feet, syndactyly (usually involving fingers III and IV in the hands and toes II to V in the feet), camptodactyly of fingers, and absent halluces. Extraskeletal malformations include malformations of the central nervous system (myelomeningocele /encephalocele, cerebellar hypoplasia, hydrocephalus), heart (congenital valvular heart defects), intestine, genitourinary system (hydronephrosis ± urethral valve/reflux, hypospadias, epispadias). Congenital corneal opacities, bilobed tongue, deafness, and Dandy-Walker malformation have been reported in a minority of OPD2 cases. Congenital glaucoma and cataracts have been described in one patient. Psychomotor development varies from normal to mild intellectual disability. Carrier females with OPD2 can be asymptomatic or exhibit a phenotype that can extend from a mild subclinical osteodysplasia to a presentation indistinguishable from that of affected males. Prognosis of OPD2 is poor and perinatal death is common, secondary to cardio respiratory failure.

Etiology

OPD2 is caused by gain of function mutations in the gene FLNA (Xq28) that encodes filamin A. However the pathogenesis is still elusive. OPD2 is allelic with 4 other skeletal dysplasias (OPD1, Melnick-Needles syndrome (MNS), terminal osseous dysplasia - pigmentary defects (TOD) and frontometaphyseal dysplasia (FMD)).

Genetic counseling

OPD2 is inherited in an X-linked dominant manner. Male-to-male transmission has not been reported. The risk of transmitting the mutation in each pregnancy is 50%; males inheriting the mutation will be affected while females who inherit the mutation are less severely affected.