Table 1.
Hypodontia frequency in the Polr3b-HLD mouse model
| Incisor size at end point (n) | ||||
|---|---|---|---|---|
| Polr3b status | Normal | Small | Absent | Total |
| Δ10/Δ10 | 0 * | 6 * | 9 * | 15 |
| +/Δ10 | 22 | 0 | 0 | 22 |
| CTRL | 41 | 0 | 0 | 41 |
The appearance of the incisors was categorized and counted at terminal end points (P14–P34) in 14 litters of Δ10/Δ10, +/Δ10 and CTRL mice. Frequencies in each incisor size group are categorized by genotype. Normal incisors were defined as incisors that were the same length as CTRL littermates. Small incisors were defined as being less than half the length of the incisors of a CTRL littermate. Absent incisors were categorized when incisors had not visibly erupted. Male and female Δ10/Δ10 mice had similar frequencies of absent incisors (5/8 females, 4/7 males) and small incisors (3/8 females, 3/7 males). In a sex-pooled statistical analysis, Δ10/Δ10 mice had a significantly smaller proportion of mice with normal incisors and greater proportion of mice with either small or absent incisors, as compared to +/Δ10s and CTRLs. Statistical analysis of incisor size and sex did not indicate dependence of these variables (not shown). Statistical significance was computed by cross-tabulation of genotype and incisor size using a Fisher-Freeman-Halton Exact test in SPSS v28.0.0.1 (IBM). The Fisher-Freeman-Halton Exact Test indicated a statistically significant association between genotype and incisor size (64.239, exact two-sided significance <0.001). The proportion of mice in an incisor size group were categorized by genotype using the Z-test of independent proportions with significance tested post hoc adjusting for multiple comparisons by the Bonferroni method (α = 0.05). Using this method, differences in the proportion of Δ10/Δ10s with normal, small, or absent incisors were evaluated as statistically different from the corresponding proportion in +/Δ10 and CTRL mice. POLR3B-HLD = RNA polymerase III subunit B-related hypomyelinating leukodystrophy; Δ10/Δ10 = tamoxifen-treated transgenic mice carrying a Pdgfrα-CreERT allele and homozygous Polr3bfl alleles; +/Δ10 = tamoxifen-treated transgenic mice carrying a Pdgfrα-CreERT allele and heterozygous Polr3bfl alleles; CTRL = tamoxifen-treated transgenic mice carrying no Pdgfrα-CreERT allele(s).
* P < 0.05.