**1. Introduction**

Autism spectrum disorders (ASD) are a group of neurodevelopmental disorders associated with severe deficits in social communication, often accompanied by restricted patterns of behaviour, activity and interests [1]. ASD prevalence has been on the rise and is currently estimated to be 1:68 with higher rates for boys (1:42) than girls (1:189) [2].

Social, communication and cognitive deficits typical for ASD can affect individual sufferers with various severity and in many different combinations, which prompted the concept of autistic continuum, later replaced by autistic spectrum [3, 4] Already in the earliest publica‐ tions on autism, Kanner [5] and Asperger [6] identified certain similarities in the untypical severity of certain traits and behaviours in children with autism and their parents, such as tendency to social withdrawal, limited interest in people, late speech development and pedantry. Further research demonstrated that autistic traits are more prevalent in the closest relatives of individuals with ASD than in other groups [7-11].

Subtle, subclinical traits or characteristics that parallel the defining features of autism, present in non-affected individuals, in particular the first-degree relatives of people with autism, are referred to as "Broader Autism Phenotype" (BAP) [10-13]. The presence of specific character‐ istics in terms of social and communication skills, cognitive processes and personality in parents and siblings of individuals with ASD may suggest genetic involvement in the aetiology of autism, what is strongly supported by evidence obtained from twin and family studies. Research in this area may expand our knowledge of the nature of autism and the mechanisms underlying the emergence of its characteristic symptoms [14].

It has been estimated that BAP characteristics may be presented in at least 10-20% of parents and siblings of children with these disorders [12, 15]. For instance, Bolton et al. [12] found out

that 12,4% of siblings of the autistic probants compared to only 1,6% of the siblings of Down's syndrome were described as performing autistic traits, but of a less severe degree. In spite of many studies considering difficulties demonstrated by relatives of children with ASD, specific determination of characteristics included in BAP requires further research.

A number of publications have described the specific personality traits of parents and siblings of children with ASD: shyness, preference to be alone, insistence on sameness, reluctance to change and obsessive-compulsive behaviours [16, 17]. There are also data on the mental health problems in members of these families [18], although the results of studies in this area are not consistent (see: [19] for review).

In addition, the relatives of children with ASD demonstrate a specific cognitive characteristics. They achieved lower scores in attribution mental states based on facial expressions tasks [20], showed weaker central coherence (e.g. [16, 20, 21]), and a lower level of efficiency in planning, attention shifting and other executive function [22-26].

Several comprehensive reviews of the few dozen years of research on BAP have been published (e.g. [7, 14, 27, 28]). In this article we will be focusing on social communication problems such as understanding body language and emotional expression, as well as specific language characteristics in parents and siblings of people with ASD. Impaired language and social communication problems are defining elements of autism and include a delay or lack of spoken language that cannot be compensated by other means of communication, difficulties in initiation and maintenance of conversation as well as repetitive and stereotypic language patterns and expressions [29]. The deficits in these domains are recognized as the key features of broader autism phenotype [13, 30, 31].

This review was conducted in the first half of 2014 using the following electronic databases of international literature: Web of Science, MEDLINE/PubMed, SCOPUS, EBSCO. The articles reviewed were published from 1992 to May 2014. Keywords related to phenotype, endophe‐ notype, autism, parents, siblings and family were used. The next step was to select studies meeting the following criteria: a) published in English; b) the social communication and language characteristics of autism in parents and siblings of individuals with autism were objects of study; c) original studies. We have excluded articles that did not explore the themes of social communication and language, those that discussed research on BAP in general population or more distant relatives of individuals with ASD rather than in their parents and siblings, as well as studies that did not include a control group.
