The trismus-pseudocamptodactyly syndrome is a distal arthrogryposis characterized by an inability to open the mouth fully (trismus) and pseudocamptodactyly in which wrist dorsiflexion, but not volar flexion, produces involuntary flexion contracture of distal and proximal interphalangeal joints. In these patients, trismus complicates dental care, feeding during infancy, and intubation for anesthesia, and the pseudocamptodactyly impairs manual dexterity, with consequent occupational and social disability (summary by Veugelers et al., 2004).

MEHMO syndrome is a rare intellectual disability disorder that exhibits phenotypic heterogeneity and is variably characterized by impaired intellectual development, epileptic seizures, hypogonadism with hypogenitalism, microcephaly, and obesity. Life expectancy ranges from less than 1 year to adulthood, and the condition is associated with significant morbidity and mortality (summary by Gregory et al., 2019).

MRD57 is an autosomal dominant neurodevelopmental disorder with a highly variable phenotype. Most affected individuals have delayed psychomotor development apparent in infancy or early childhood, language delay, and behavioral abnormalities. Additional features may include hypotonia, feeding problems, gastrointestinal issues, and dysmorphic facial features (summary by Reijnders et al., 2018).

Jeffries-Lakhani neurodevelopmental syndrome (JELANS) is an autosomal recessive disorder characterized by hypotonia, early-onset seizures, and global developmental delay apparent from infancy. Affected individuals have motor delay, speech delay, and impaired intellectual development, and about half of patients are nonambulatory and/or nonverbal. Some patients have cardiac arrhythmia, but congenital cardiac septal defects are only rarely observed. Additional features may include feeding difficulties, recurrent infections, ocular defects, and nonspecific dysmorphic features. Premature death due to cardiac arrhythmia or epilepsy may occur (Jeffries et al., 2024).