Familial aggregation of any medical phenotype gives us the scientific basis to suggest that genes are involved and are important in the etiology of such phenotypes. Developmental delays/ mental retardation and learning disorder, attention deficit disorder of childhood-ADHD and speech disturbances are common (12.5%). In all of these disabilities, the familial aggregation is well known. Although several genes and several mutations were described in such phenotypes, we think that most of the responsible genes are still unknown. Her we describe in brief three consanguineous families that present unique medical picture but in all of these families the developmental delay/MR or learning disorder were relatively common and part of the clinical presentation. The first family presents morbid obesity and metabolic syndrome all the of the 13 adult affected individuals except than one, learned maximum 12 years and did not achieve the required qualification to continue for college or university studies. Three of them present mild mental retardation. Linkage study and subsequent haplotype analysis and sequence analysis identified a novel gene, highly conserved throughout vertebrate and invertebrate species, encoding a homozygous nonsense mutation in all affected family members. The gene was found to be highly expressed in multiple tissues. In the second family all the affected individuals were females. All the patients present with a complicated phenotype that includes: mild to severe cerebral palsy; congenital hypertension and learning disabilities. Further evaluation revealed high plasma rennin- aldosteron levels with normal renal artery and kidney Echo- Doppler studies. We mapped and cloned a novel gene that was mutated in our patients.
A third family presents a wide spectrum of neurological disability with developmental delay, gait abnormality, ataxia, and mild to moderate MR, learning disorder and speech disturbance. Moreover, all of the affectd children were found to have cataract within the first decade of life. The pedigree in this highly consanguinity family demonstrates a clearly inherited autosomal recessive transmitted unique disorder. We start to characterize and evaluate the disease in this family.
We believe that a thorough medical history assessment especially in the Arab community may uncover several monogenic inherited cognitive and neurological abnormalities.
Our takeoff message is: find and characterize the familial cases of cognitive abnormalities and maximize the chances to clone the mutated genes.