**3.1 Family studies**

Hereditary combination of a trait or disorder will recommend genetic aetiology. Hereditary patterns may additionally indicate exposure to common environmental factors within these families. Familial aggregation could result from shared genes, shared environmental exposures and behavioural risk factors like education, socio economic grouping, oral hygiene, possible transmission of bacteria, diseases like polygenic disorder, passive smoking, exposure to pollutants and sanitation. Therefore, the complex interactions between genes and also the surroundings should even be thought-about in the analysis of familial risk for periodontic diseases [14].
