Importance of early audiologic assessment in distal renal tubular acidosis

Figures & data

Figure 1 The distal nephron apical H⁺ATPase. Although the multisubunit H⁺ATPase is ubiquitously expressed, a specialized version is found at high density at the apical (urinary) surface of intercalated cells, mostly in the collecting duct. A) This type of pump is studded along the plasma membrane in an electron micrograph of the turtle urinary system (image courtesy of Professor P Steinmetz). B) General structure of H⁺ATPases. In the kidney, the B and a subunits (hatched) are composed of the genetically distinct B1 and a4 forms, whereas generic intracellular pumps contain B2 and a1 subunits.

Table 1 Details of restriction fragment length polymorphisms used in this study

Single nucleotide polymorphism	Site	Amino acid position and change	Enzyme	PCR product sizes before → after digest (bp)
ATP6V0A4
rs10258719	Exon 3	A2V	BgII	299 → 149 + 150
rs1026435	Exon 16	F554F	XcmI	262 → 157 + 105
rs3807154	Exon 17	H604H	BsaAI	323 → 174 + 149
ATP6V1B1
rs2266918	Exon 2	S46S	TspRI	282 → 123 + 159
rs967063	Intron 3		HpyCH4IV	470 → 237 + 233
*	Exon 6	E161 K	AvaI	251 → 66 + 185
rs2072462	Exon 10	R334R	BstUI	267 → 120 + 147

Note:

* ATP6V1B1 exon 6 single nucleotide polymorphism is novel.

Abbreviations: PCR, polymerase chain reaction; bp, base pairs.

Figure 2 Genotyping of kindred. Single nucleotide polymorphisms in A) ATP6V0A4 and in B) ATP6V1B1 were subject to polymerase chain reaction amplification followed by specific restriction digestion, and this was used to assess linkage to both genes. Details of these single nucleotide polymorphisms are shown in Table 1. Filled symbols are affected individuals whereas unfilled symbols are unaffected individuals. Arrow denotes index case. C) Mutations in ATP6V0A4 were identified by DNA sequencing. Upper traces are representative of the heterozygous alterations in codon 770 and 807 in both children and one affected parent. Lower traces show wild-type sequences from the unaffected parent. Translation products of the sense strand are shown, with altered products in color. In codon 770, the C > T transition introduces a premature stop codon. In codon 807, the G > A transition results in the substitution of glutamine for arginine.