Low Prevalence: Mutations in these genes are found in less than 10–20% of familial stuttering cases, meaning they account for a small fraction of all stuttering instances. Most stuttering cases (especially non-familial) lack these mutations. Polygenic Nature: Stuttering is considered polygenic, meaning multiple genes and environmental factors contribute. These four genes are not sufficient to predict stuttering alone, as other unidentified genes (e.g., ZMAT4, FAM49, or PPID from recent studies) and non-genetic factors like stress or language development also play roles. Population Specificity: The mutations were primarily identified in specific populations (e.g., consanguineous Pakistani families), limiting their generalizability. For example, AP4E1 mutations were significant in North American and Cameroonian cases but not always in Brazilian controls. Incomplete Penetrance: Not everyone with these mutations stutters, and some who stutter lack them, reducing their predictive reliability. This is evident in studies showing variable expression even within families. Lack of Clinical Tests: There’s no widely available genetic test for stuttering based on these genes, and their predictive power hasn’t been quantified in large, diverse populations. Current research focuses on understanding mechanisms rather than developing predictive models.