Clinical examination for hyperlinear palms to determine filaggrin genotype: a diagnostic test accuracy study

BACKGROUND: Palmar hyperlinearity is a feature of ichthyosis vulgaris, the monogenic skin disorder caused by FLG loss-of-function mutations.

OBJECTIVE: To investigate how well the presence or absence of hyperlinear palms (HLP) detect FLG genotype in children.

METHODS: STARD criteria are used to report this diagnostic accuracy study. Phenotype and genotype data (four most prevalent FLG null mutations) were obtained from a total of 3656 children in three studies: the UK CLOTHES trial (children 1-5 years with moderate-severe atopic eczema); UK BEEP trial (2-year-olds at high risk of developing atopic eczema); UK-Irish eczema case collection (0 to 16-year-olds with atopic eczema). All participants included in analyses of HLP as the index test and FLG genotype as the reference were of white European ancestry.

RESULTS: 32% of participants (1159/3656) had FLG null mutation(s) and 37% (1347/3656) had HLP. In 13% (464/3656) HLP was recorded as 'unsure' or not recorded. The sensitivity and specificity of HLP for detecting FLG mutations in each of the studies was: 67% (95% CI 55-78%) and 75% (67-82%) in CLOTHES; 46% (36-55%) and 89% (86-91%) in BEEP; 72% (68-75%) and 60% (57-62%) in the UK-Irish case collection. Positive and negative likelihood ratios were: 2.73 (1.95-3.81) and 0.44 (0.31-0.62) in CLOTHES; 4.02 (2.99-5.40) and 0.61 (0.52-0.73) in BEEP; 1.79 (1.66-1.93) and 0.47 (0.42-0.53) in the UK-Irish collection.

DISCUSSION: Trained observers were able to define palmar hyperlinearity in the majority (3191/3656, 87%) of cases. The presence of HLP is not a reliable sign to detect FLG mutations, but the absence of HLP excludes FLG null genotype with a reasonable degree of certainty. Registration This retrospective study was not pre-registered.