Severe Elimination Disorders and Normal Intelligence in a Case of MAP1B Related Syndrome: A Case Report

Pathogenic variants in the MAP1B gene have been associated with neurological impairment, including intellectual disability, attention-deficit/hyperactivity disorder (ADHD), autism spectrum disorder, brain malformations, cognitive hearing loss, short stature, and dysmorphic features. However, few cases with detailed clinical characterization have been reported. We describe a 12-year-old boy carrying a loss-of-function MAP1B variant, presenting with severe elimination disorders despite normal intelligence. He was referred to the genetics service due to persistent elimination issues, including daytime urinary incontinence, nocturnal enuresis, and fecal incontinence. He had normal motor and cognitive development, with an IQ of 99; however, he also presented with ADHD, short stature, microcephaly, and myopia. Brain MRI revealed bilaterial subependymal periventricular nodular heterotopia (PVNH). Audiometry showed normal bilateral hearing. Testing fragile X syndrome (FXS) and karyotype analyses yielded normal results. Whole exome sequencing (WES) revealed a nonsense pathogenic variant in MAP1B (c.895 C>T; p.Arg299*). No other family members showed a similar phenotype; however, a great-uncle and a great-aunt had a history of nocturnal enuresis until age 10. The patient's deceased mother had short stature and psychiatric disorders, and a history of consanguinity was reported on the maternal side. This case broadens the phenotypic spectrum associated with MAP1B syndrome, suggesting that elimination disorder, frequently reported in FXS, should also be evaluated in MAP1B pathogenic variant carriers. In addition, the presence of short stature also appears to be part of the syndrome.