Childhood Hearing Impairment in Senegal

Abstract

We recently showed that variants in GJB2 explained Hearing Impairment (HI) in 34.1% (n = 15/44) of multiplex families in Senegal. The present study aimed to use community-based nationwide recruitment to determine the etiologies and the clinical profiles of childhood HI in Senegal. Participants with early onset HI were included after clinical examination, including audiological assessment by pure tone audiometry and/or auditory brainstem response. We investigated a total of 406 participants from 295 families, recruited from 13/14 administrative regions of Senegal. Male/female ratio was 1.33 (232/174). Prelingual HI was the most common type of HI and accounted for 80% (n = 325 individuals). The mean age at medical diagnosis for congenital HI was computed at 3.59 ± 2.27 years. Audiological evaluation showed sensorineural HI as the most frequently observed HI (89.16%; n = 362 individuals). Pedigree analysis suggested autosomal recessive inheritance in 61.2% (63/103) of multiplex families and sporadic cases in 27 families (26.2%; 27/103), with a consanguinity rate estimated at 93% (84/90 families). Genetic factors were likely involved in 52.7% (214/406) of the cases, followed by environmental causes (29.57%; 120/406). In 72 cases (17.73%), the etiology was unknown. Clinically, non-syndromic HI was the most common type of HI (90.6%; n = 194/214 individuals). Among families segregating syndromic cases, type 2 Waardenburg syndrome was the most common (36.3%; 4/11 families). This study revealed putative genetic factors, mostly associated with high consanguinity rate, as the leading causes of early-onset HI in Senegal. The high consanguinity could provide a good opportunity to identify variants in known and novel genes involved in childhood HI.

Keywords: Africa; Senegal; causes; childhood; consanguinity; hearing impairment.

Figure 1

Regional distribution of 295 families living with HI in Senegal. More families were recruited from the Western regions, particularly in Dakar. The majority (n = 262; 64.53%) of participants were recruited from schools for the deaf across the country (Supplementary Material Table S1). Only one administrative region has not been covered during the recruitment. The numbers on the figure correspond to the families recruited in each administrative region.

Figure 2

Typical modes of inheritance found in our cohort. (A) Pedigree of a consanguineous family with autosomal recessive non-syndromic hearing impairment. (B) Pedigree of a family with non-syndromic hearing impairment suggestive of X-linked recessive inheritance. (C) Pedigree of a family with autosomal dominant non-syndromic hearing impairment. Probands are indicated by arrows.

Figure 3

Two families with Waardenburg syndrome type 2. In the first family (A) the proband (C) exhibited white forelock, sapphire blue eyes, and hypopigmented skin patches associated with profound sensorineural HI (B). In the second family (D), the proband (F) showed light skin, white hair, and profound HI (E), while his brother (H) exhibited sapphire blue eyes and light skin associated with profound HI (G).

Figure 4

Patient with a suspected Labyrinthine Aplasia, Microtia, and Microdontia syndrome. The photo is illustrating a 7-year-old girl showing unilateral microtia (Type 3) (A), microdontia with wide-spaced teeth (B), periauricular skin tags (C), profound hearing loss in the right ear while the left ear exhibited moderate hearing loss (D), and asymmetrical face (E). The pedigree (F) suggests an autosomal recessive pattern of inheritance. The arrow indicates the proband.

Figure 5

Pedigree showing four affected individuals from a consanguineous marriage segregating Pendred syndrome. The arrow indicates the proband.

Figure 6

Pedigree of a multiplex family showing three affected girls from a non-consanguineous marriage segregating Diabetes-deafness syndrome. The arrow indicates the proband.

Figure 7

Pedigree showing three affected individuals segregating Usher syndrome. The arrow indicates the proband.

Figure 8

Pedigree of a simplex family with Down’s syndrome. The arrow indicates the proband.

Figure 9

Pedigree showing six affected individuals segregating likely Alport syndrome. The arrow indicates the proband.

Figure 10

Pedigree showing two affected individuals from a non-consanguineous marriage. The arrow indicates the proband.