I don’t remember you being diagnosed, but I know I was nearly seven and you were nearly two. I do remember the metal braces that were strapped to your ankles for extra support when you were learning to walk, while other children your age tore around us.

I do remember crying on a walk home from primary school after being told that you needed glasses, because I couldn’t stop thinking, hasn’t he got enough to deal with already? I do remember lying in bed, praying to someone who even then I didn’t believe existed that I might wake up the next morning and find you miraculously “normal”.

But the brilliant truth is, you are blissfully and completely unaware of your differences. You live the naive and joyful life of a five-year-old in a 25-year-old’s body. You are incapable of malice. You crave the praise of those you consider most important – your mother, of course; me; your other sisters; and the amazing people who guide you patiently through your new independent life in the community.

You take immense pleasure from the simplest things. A story told for the thousandth time by our snoozy father, your hero, on a Sunday afternoon. The sound of a foreign emergency vehicle siren. Having the last sip of someone else’s drink.

You have some exceptional gifts, as those with comparable conditions often do. Playing “beat the intro”, you can name the song, seemingly before the first note is played. You can recall the names of staff from hotels we stayed in years ago, when the rest of us can’t even remember the hotel. You can, terrifyingly, get through international airport security without either passport or boarding pass, only getting caught trying to enter a lounge.

I try not to mourn the life you haven’t had. It’s easy when I remember that you live in a world without sadness, fear, guilt. It’s easy because everyone who meets you falls in love with you – so I know that, wherever you are, someone will be looking out for you. Even my one-year-old daughter can’t take her eyes off you.

I could write for ever about the moments with you that have changed us. You have made us kinder, softer and immeasurably happier – but you will never know it. Your sister, Rachel

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