Paediatric neurology syndromes are a broad and complex group of conditions with 
a large spectrum of clinical phenotypes. Joubert syndrome is a genetically 
heterogeneous neurological ciliopathy syndrome with molar tooth sign as the 
neuroimaging hallmark. We reviewed the clinical, radiological and genetic data 
for several families with a clinical diagnosis of Joubert syndrome but negative 
genetic analysis. We detected biallelic pathogenic variants in LAMA1, including 
novel alleles, in each of the four cases we report, thereby establishing a firm 
diagnosis of Poretti-Boltshauser syndrome. Analysis of brain MRI revealed 
cerebellar dysplasia and cerebellar cysts, associated with Poretti-Boltshauser 
syndrome and the absence of typical molar tooth signs. Using large UK patient 
cohorts, the relative prevalence of Joubert syndrome as a cause of intellectual 
disability was 0.2% and of Poretti-Boltshauser syndrome was 0.02%. We conclude 
that children with congenital brain disorders that mimic Joubert syndrome may 
have a delayed diagnosis due to poor recognition of key features on brain 
imaging and the lack of inclusion of LAMA1 on molecular genetic gene panels. We 
advocate the inclusion of LAMA1 genetic analysis on all intellectual disability 
and Joubert syndrome gene panels and promote a wider awareness of the clinical 
and radiological features of these syndromes.